Issuu

MUESTRA

Rafael Jiménez Prieto Pastora M.ª Torres Verdugo

E S O

A guide to your book With the book you are holding you will: ➜ Gain insights into Physics and Chemistry employing the 5-stage methodology, mirroring the Spanish version: Engage, Explore, Explain, Elaborate, and Evaluate. ➜ Enhance and expand your English skills through activities designed for practicing written and oral comprehension and expression.

Introduction A learning experience related to Andalusia is explored through the following steps: Engage. A motivational video related to the unit’s content. Explore. Activities to investigate the situation. Elaborate. Activities to apply the concepts.

Main content The left-hand pages focus on presenting content in the Explain phase. On the right-hand pages, you’ll find a variety of activities designed to reinforce the content.

End of section The final step of the 5-stage model, Evaluate, is completed with an assessment at the end of each section. The term closes with a double-page spread that includes texts and activities related to some of the topics covered during the term.

Index 1 Quantities and their measurements. Scientific work

2 The structure of matter. Groups of atoms

3 Elements and compounds. The periodic table

Evaluate. Practise in English

4 Chemical reactions. Introduction to stoichiometry

5 Forces and their effects. Laws of motion

6 Forces in nature (I). Gravitation

Evaluate. Practise in English

7 Forces in nature (II) Electricity and magnetism

8 Electric circuits. Electrical energy

9 Science and society. The sustainable development challenge

Evaluate. Practise in English

UNIT

1 Quantities and their measurements. Scientific work

Andalusia and agriculture With its ideal geographical conditions, Andalusia is and has always been a haven for farming and agriculture. Drawn by the fertile soil and mild climate across large areas of the region, several civilizations settled here and became prosperous from farming and mining activities. These days, agriculture in Andalusia has improved with modern technology, seeking to optimise yield and resource efficiency. Chemistry plays an important role in these developments. In groups and following instructions from your teacher, you will work on agriculture in Andalusia and how it is closely linked to chemistry.

Explore 1 Modern farms require a well-planned and well-designed infrastructure. Who help

farmers with this task and how do they do so? Give an example. 2 Which crops are grown in Andalusia and where? Who are the end consumers? 3 Agriculture relies heavily on chemistry for fertilizers, pest control and quality

certification. Find out more information about this. 4 Scientific research plays a big role in improving the profitability and sustainability

of agriculture. Where and how does this research take place in Andalusia?

Elaborate 1 Based on your findings, prepare a presentation about agriculture in Andalusia and

how it is related to chemistry. 2 Make sure you include graphs, pictures or photos and quote your sources. 3 On the last slide, present your conclusions and the group’s opinion.

Communicate 1 Each group will present their findings, conclusions and opinion to the rest of the

class. 2 You can follow up with a class discussion about the importance of the agriculture

sector in Andalusia and the advantages and disadvantages of using chemistry to increase yield.

1 What is the work of a scientist? How does each new scientific discovery become accepted fact and how is it studied? Drawing valid conclusions involves systematic work that we can review, which is characteristic of the experimental sciences. The scientific method is a systematic and controlled process that allows us to study an observed phenomenon and establish the models and laws by which it is ruled. The scientific method consists of several stages, which are completed in order. Observation. An unexplained phenomenon is observed and as much detailed information as possible is collected.

Constructing a hypothesis. A reasoned explanation about the phenomenon under study is proposed. This explanation must be validated or rejected, if it turns out to be incorrect.

Experimentation. The crucial phase of the scientific method, as it will determine whether the hypothesis is valid or not. We make predictions from the formulated hypothesis, which we must check by carrying out experiments under controlled conditions.

Once a hypothesis has been validated through experimentation, it becomes a scientific law. The law is usually expressed as a mathematical formula that relates the quantities involved in the phenomenon studied. Meticulous scientific research calls for us to record the steps taken, describe how we have processed the data obtained and draft the conclusions drawn from the study. We compile all of it in a scientific report.

Observation.

Title of the report, authors and date. 1 Introduction. We describe the observed phenomenon and mention the objectives.

Analysis of the results. We write down the data, perform the calculations and interpret the results.

Experimental process. We explain the process followed and describe the material used and the setup.

5 4

Final conclusions. We draw conclusions based on analysis of the results.

6 Bibliography. We mention the books, journals, etc. we have used, indicating their title and author.

UNIT 1

1. Look up the names of three important scientists in books or on the Internet and write down their main discoveries. Choose one of them and prepare a card about what you consider to be their most noteworthy contribution. 2. The famous French scientist Louis Pasteur, who discovered the vaccine for rabies, once said:

«In the field of observation, chance favours only the prepared mind».

What do you think he meant by that? Explain this to your classmates. 3. You will find articles describing research in the fields of medicine, biology… in specialised scientific journals and on the Internet. Choose one of those articles and use it to try and identify some of the common sections of scientific reports. Pay special attention to the objectives, the work method and the final conclusions. 4. Indicate which terms, related to the scientific method, correspond to each of the following statements:

7. It is a well-known fact that iron objects exposed to the elements oxidise easily. a) Carefully observe different iron objects, oxidised or not, and take note of the data you consider relevant about this phenomenon. b) Prepare a hypothesis that justifies why iron objects oxidise outdoors. c) What experiment can you design to check the validity of the hypothesis? Which measurements must you take? d) Based on the conclusions drawn from the research, what can we do to avoid iron objects oxidising quickly?

a) It is essential that we check whether a formulated hypothesis is valid or not. b) This is what a hypothesis becomes once it has been fully validated. c) It compiles all the research carried out and we use it to let other scientists know about this research. d) If done thoroughly, it can lead to a discovery. 5. Answer the following questions: a) Why do we say that the scientific method is characteristic of the experimental sciences? b) What happens if the experimental results do not coincide with those foreseen by the hypothesis we initially proposed? c) How important is a scientific report? 6. You already know that some scientific discoveries took place completely by chance. a) Look up the meaning of the word serendipity. How is it related to the above? b) One of those discoveries was saccharin, a known sweetener. Research how it took place. c) Prepare a card with the information you have compiled, and include a final comment about the subsequent transcendence this discovery may have had.

8. Listen and define the following terms in your notebook based on what you have learnt in this section: Scientific method. Hypothesis. Experimentation. Scientific law. Formula. Scientific report. 9. Draw a flow chart to summarise the contents of this section. Remember that you can add the definitions or explanations from the previous exercise.

Quantities and their measurements. Scientific work

2 Which quantities and units do we use? In an experiment, we obtain quantitative information by measuring the observable properties of the phenomenon we are studying. A quantity is any property that can be measured. Measurement is a process of determining how large or small a quantity is as compared to a basic reference quantity of the same kind. A unit is a particular amount of some quantity used as a reference point for measurements of that quantity, assigned the value of 1 by convention. Base quantities are quantities that cannot be defined in terms of other quantities. They are the simplest and the most frequently used quantities, such as length, mass or time. The remaining quantities are defined from the base quantities and we call these derived quantities. Base Quantity Measurement The International System of quantity symbol unit Units (SI) is a convention / Length Metre accepted by the scientific community, which establishes Time t Second the base quantities and their Mass m Kilogram units of measurement.

Prefix

Kelvin

Current

Ampere

Luminous intensity

Candela

Amount of substance

Mole

mol

Unit equivalence

Example: time (s)

peta-

1000000000000000 (1015)

1 Ps = 1015 s

T-

tera-

1000000000000 (1012)

1 Ts = 1012 s

G-

giga-

1000000000 (109)

1 Gs = 109 s

M-

mega-

1000000 (106)

1 Ms = 106 s

kilo-

1000 (103)

1 ks = 103 s

hecto-

100 (102)

1 hs = 102 s

da-

deca-

1 das = 10 s

Unit equivalence

Example: mass (g)

Prefix

deci-

0.1 (10–1)

1 dg = 10–1 g

centi-

0.01 (10–2)

1 cg = 10–2 g

milli-

0.001 (10 )

1 mg = 10 g

µ-

micro-

0.000001 (10 )

1 µg = 10–6 g

nano-

0.000000001 (10–9)

1 ng = 10–9 g

pico-

0.000000000001 (10–12)

1 pg = 10–12 g

femto-

0.000000000000001 (10–15)

1 fg = 10–15 g

UNIT 1

P-

Symbol

–3

–6

–3

peta-

tera-

giga-

mega-

kilohectodecadecicentimilli-

micro-

nano-

pico-

femto-

MULTIPLES

Symbol

Temperature

SUBMULTIPLES

In addition to the units for each quantity, the International System establishes prefixes to express multiples or submultiples of each unit.

Unit symbol

10. Explain the meaning of quantity, measurement and unit, and give an example in each case. 11. What advantages do you think there are in having a convention like the International System of Units compared to using different traditional units from each area or country?

16. Perform the following unit conversions clearly indicating all the steps followed in each case. Remember that you must use conversion factors. a) 50 hm3 in m3.

b) 0.056 L in cm3.

c) 5.2 g/cm3 in g/mL.

d) 150 km/h in m/s.

e) 0.34 m/s in km/h.

f) 85 kg/m3 in g/cm3.

Discuss this with your classmates.

g) 16 g/L in kg/m3.

h) 45 µL to mg/mL.

12. Use books or the Internet to see how the definition of metre, the unit of length, has evolved since the International System was introduced. In your opinion, how is this related to the scientific method?

17. Ana is carrying out an experiment in the chemistry laboratory. She measures 75 cm3 of water with a measuring cylinder and she places it in a container. Ana adds 3.5 mL of water that she has measured with a pipette to that same container and 2.7 cL of water using a burette. What is the total volume of water that Ana has added to the container? Express the result in litres and in the unit that the International System uses for volume. 18. A communication satellite rotates in geostationary orbit around the Earth at a speed of 11,040 km/h. A supersonic jet can reach a speed of 600 m/s. Which of these two vehicles reaches the highest speed?

13. Choose one of the base quantities of the International System. For the base unit of this quantity, draw two complete tables of multiples and submultiples, with their corresponding names and equivalences. Use scientific notation. 14. Write the two equivalences that correspond to the following pairs of multiples and submultiples of the unit of length of the International System. Use scientific notation, if necessary: a) Between Gm and m. b) Between ms and ms. c) Between km and Gm. d) Between mm and nm. e) Between Tm and Mm.

19. Listen and define the following terms in your notebook, based on what you have learnt in this section:

f) Between Mm and cm.

Quantity.

15. Perform the following base unit conversions indicating their quantity in each case:

Measurement.

a) 2700 kg in Mg.

International System.

b) 600 µA in mA. c) 0.0065 Gs in Ms. d) 72,000 nmol in mmol. e) 45 ºC in K.

Unit. 20. Draw a flow chart to summarise the contents of this section. Remember that you can add the definitions or explanations from the previous exercise.

Quantities and their measurements. Scientific work

3 How do we measure and process data? We measure quantities using a specific measuring instrument or device. Scientific instruments must be precise to ensure reliable results. They must also be highresolution to detect small variations in the measurements. The data must be processed to be able to intepret it properly. ➜ Tables are the the best way to collect numerical data. ➜ We draw graphs based on the data in the tables to interpret the dependence between the quantities studied. ➜ Once we establish the mathematical dependence between the quantities, this gives rise to a formula. The formula shows the quantities involved in the phenomenon linked by mathematical operations.

4 How does the science laboratory work? An experiment is designed to validate or refute a hypothesis and must be performed under careful, controlled conditions as the progress of the research depends on the result. The laboratory is an area designed and equipped with the necessary material and measuring instruments for scientific experimentation. When we work in a chemistry laboratory, we often have to handle various substances in different states of aggregation. We therefore have a wide range of glass containers and devices, which we generally refer to as laboratory apparatus.

Graduated pipette

Beaker

UNIT 1

Erlenmeyer flask

Measuring cylinder

Calibrated flask

Rack, test tubes

Burette

Wash bottle

Digital gram scale

Funnel

Spatula

21. The clocks we have at home are instruments for measuring time.

a) Draw a graph using the data above. Place the mass on the abscissa axis and the extension on the ordinate axis. b) What is the dependence between both quantities? What do you base your answer on? c) Which formula could you propose to express this dependence? Write it down. d) Using the formula above, calculate the value of the mass that will cause this spring to extend by 12 cm.

a) Do you think they are exact and accurate instruments? Explain this. b) What resolution do these type of clocks have? c) According to the above, do you think they are suitable instruments for scientific use?

25. Explain why we must carry out scientific work in a laboratory. What are the essential safety rules that we must follow in the school laboratory, and indeed any laboratory? 26. Answer the following questions in your notebook about a chemistry laboratory: a) What are chemical reagents?

22. To measure length, there is an instrument with a higher resolution than classic tape measures: the nonius or gauge.

b) What is the function of a gas extractor hood?

Using a nonius, Laura has measured the thickness of a coin and has obtained a result of 0.34 cm. Toni has repeated the same measurement and got a result of 0.35 cm.

d) Is it possible to light a fire?

a) What is the resolution of the nonius? b) How can we explain the fact that both pupils, who have used the device correctly, obtained different results? 23. Indicate the quantity we measure with each of the following instruments which we can find in any laboratory:

c) Why do we sometimes have to use protective equipment such as goggles or gloves? 27. Indicate what you would use in each case in the laboratory: a) To contain substances, usually liquids. b) To measure liquid volumes with low accuracy. c) To prepare solutions. d) To measure the mass of a substance.

a) pH meter.

e) To accurately measure small volumes of liquid.

b) Thermometer.

f) To take small portions of solid substances.

c) Multimeter.

28. Most of the material used in the chemistry laboratory is made of glass and in some cases porcelain, despite the fact that both materials are fragile and break easily.

d) Graduated pipette. e) Gram scale. f) Stopwatch. 24. Virginia and Angel are performing an experiment in their school’s laboratory. This involves measuring the extension of a spring by hanging weights of different masses from it.

Why do you think these materials are used and not others, such as plastic or metals, for example? Try to give reasons for your answer. 29. Listen and define the following terms in your notebook, based on what you have learnt in this section: Measuring instrument or device.

The results appear in this table: Mass (g)

100

200

300

400

Extension (m)

0.05

0.10

0.15

0.20

Laboratory. Laboratory apparatus. Measuring cylinder. Gram scale. 30. Draw a flow chart to summarise the contents of this section. Remember that you can add the definitions or explanations from the previous exercise.

Quantities and their measurements. Scientific work

UNIT

2 The structure of matter. Groups of atoms

El Cabril, a waste disposal facility Radioactivity is one of the most-studied and most-applied phenomena of the 20th century. It was first discovered in 1896 and a few decades later scientists realised that many chemical elements were radioactive, which were soon used to create large amounts of energy at nuclear plants around the world. As well as being potentially hazardous, a major drawback of nuclear plants is that they generate waste, which needs to be stored properly until it is no longer radioactive. These waste disposal facilities must be carefully located and planned in detail. In groups and following instructions from your teacher, you will work on one such facility, in the province of Córdoba: the El Cabril disposal facility.

Explore 1 A number of energy conversions take place at a nuclear plant which finally produce

electricity. Draw a diagram to show those conversions. 2 Are nuclear plants safe? Why is radioactive waste generated at a nuclear plant and

how is it sorted? Use the Internet and recent news articles to help you with your research. 3 Which requirements must a site meet to be the location for a nuclear waste storage

facility? Analyse whether El Cabril meets those requirements. 4 Find out information about the El Cabril waste storage facility from when it was

opened until the present day. You can consult its website.

Elaborate 1 Based on your findings, you are going to create a poster about the El Cabril waste

storage facility. 2 Use a suitable computer program, focus on well-organised information, making

sure to include figures, interesting facts and photos, and quote your sources.

Communicate 1 Once you have finished your poster, you can present the information and your

conclusions to your classmates. 2 You can end with a debate about nuclear waste management being one of –but not

the only– drawbacks of producing electricity at nuclear power plants.

1 What is the matter that surrounds us made of? Chemistry is the science that studies matter, its properties, composition, structure and the changes it undergoes. Matter is anything that has mass and occupies space, in other words, it has volume. Matter is presented in limited portions, which are generally referred to as material systems. Portions of matter with a shape are called bodies. A specific type of matter is called a substance. We can understand the properties of matter and its changes in state at the microscopic level. The kinetic-molecular theory explains this: matter is formed by particles that are always in motion, the speed of which is related to the temperature.

In a gas, the particles move around and at random, because there are no forces of attraction between them.

2 When was the idea of the atom developed? The idea of the atom was first proposed by the Greek philosophers, but it was not until around the year 1800 that English chemist and professor John Dalton put forward his atomic theory, which basically said: Elements are formed by small indivisible and indestructible particles called atoms.

Atoms of a given element are identical in mass and properties, and atoms of different elements have a different mass and properties. Atoms of elements combine to form compounds in wholenumber ratios.

1:1

Hydrogen chloride is formed by the combination of atoms of chlorine (Cl) and hydrogen (H) in a ratio of 1:1, regardless of the preparation method that we use.

The electron was discovered at the end of the 19th century, in cathode-ray tubes. This revealed that the atom was not indivisible and was formed by smaller particles, called subatomic particles.

Electrons, represented by the symbol e–, are particles with a tiny mass compared to the mass of a proton or neutron and are negatively charged.

CO2

Protons, represented by the symbol p+, are particles with a mass around 1,840 times bigger than the mass of an electron, and are positively charged, equal in magnitude to the charge of an electron. Neutrons, represented by the symbol n, are particles with a similar mass to the mass of a proton, but with no electrical charge – they are neutral.

O Electrons (e–)

Protons (p+) Neutrons (n)

Atom. 14

UNIT 2

1. State whether these statements are true or false, based on Dalton’s atomic theory:

6. Electrons have a very small electrical charge.

a) Atoms can be divided into particles..

b) Calculate approximately how many electrons would be needed for a total charge of 15 C.

b) A compound is made up of atoms of elements combined in a fixed ratio. c) Atoms differ from each other in mass and properties. d) Two different elements can be formed by identical atoms. e) Two atoms of an element can combine with a single atom of another element. f) Atoms of an element change when they undergo a physical or chemical process.

a) How much is it in coulombs?

7. Calculate the number of protons needed to give a total mass of 1 g. How many electrons would we need to get the same mass? 8. Correct the mistake in the following statements: a) An electron is a particle with a very small mass and with a positive electrical charge. b) A proton has a much bigger mass than a neutron, which is roughly the same as an electron’s mass. c) A neutron has the same charge as an electron, but with a different plus or minus sign. d) Electrons and protons repel each other because they have opposite plus or minus signs.

Plants, soil, air and living things are all composed of matter.

2. The atomic model of Greek philosopher Democritus (5th century BC) is not a scientific theory, whereas Dalton’s atomic theory is (even though we now know that it is not correct). a) What do both have in common? b) Explain the difference between a scientific theory and a philosophical doctrine. 3. Use the kinetic-molecular theory to explain the following properties of solids, liquids and gases. a) A solid cannot be compressed. b) A liquid does not have a fixed shape and adopts the shape of its container. c) Gases can be compressed easily. d) Solids have a fixed shape. e) Liquids and gases flow easily. f) A liquid has a fixed volume. 4. Write a brief answer to these questions: a) Which subatomic particle does not have an electrical charge? b) Which is the particle with the smallest mass?

Chadwick’s experiment.

9. The neutron was the last subatomic particle to be discovered, in the year 1932. Look up information in chemistry books or the Internet and create a data sheet, including the name of the person who discovered it and a description of the experiment (with an illustration). 10. Listen and define the following terms in your notebook, based on what you have learnt in this section. Matter. Atom (according to Dalton). Subatomic particles. Electron.

c) Which subatomic particles have an electrical charge?

Proton.

d) How do the masses of subatomic particles compare to each other?

Neutron.

5. Consult scientific books or the Internet for information about the electrical charge and mass of the three subatomic particles. Display the information in a table.

11. Draw a flow chart to summarise the contents of this section. Remember you can add the definitions or explanations from the previous exercise.

The structure of matter. Groups of atoms

3 What are the different atomic models? The first atomic model was proposed by Joseph John Thomson. It was very simple and was short-lived. Thomson believed the atom was a solid, compact sphere with a positive charge, inside which electrons, with a negative charge, were embedded. The atom is neutral because the opposite charges cancel each other out. In 1911, Ernest Rutherford performed an experiment that concluded that the atom could not be compact. He proposed a new model: Rutherford described the atom as having a tiny, positively charged nucleus, in which the majority of the mass is concentrated, surrounded by a cloud of negatively charged electrons circulating a high speed. Since the charges of the nucleus and the electron cloud cancel each other out, the atom is neutral. There were still some experimental results yet to be explained though. In 1913, Danish physicist Niels Bohr modified Rutherford’s model. Bohr described the atom as having a positive nucleus and negative electron cloud. The electrons orbit at fixed distances from the nucleus, called energy levels, which are stable. The electrons can jump from one level to another, absorbing or emitting the extra energy.

From top to bottom: Thompson, Rutherford and Bohr’s atomic models.

4 What is our current knowledge of the atom? Although the atomic model we have today is a lot more complex, it shares some common ground with Bohr’s model. Basically it says that: The atom consists of a nucleus in which the majority of the mass is concentrated. The nucleus contains the protons and neutrons which are attracted to each other by nuclear forces that prevent repulsion.

This is surrounded by a cloud of electrons – there are same number of electrons as protons – that circulate at almost light speed and are attracted by electric forces due to their negative charge. 16

UNIT 2

Electrons are arranged in concentric circles around the nucleus. These levels increase in energy the further they are from the nucleus and the electrons are placed from the nucleus out. Electrons can jump from one level to another, absorbing or emitting the extra energy.

12. A model is a simplified description of reality and is used to explain observed phenomena. Why do you think we need a model for the atom? 13. For a model to be considered valid, it must prove experimental results. If we take the first atomic model, proposed by Thomson, is it in agreement with subatomic particles existence? 14. Rutherford’s experiment (see illustration) played a decisive role in changing the view of the atom at the turn of the 20th century. Consult your Physics and Chemistry book and write a six or seven-line paragraph explaining what the experiment entailed and the conclusions Rutherford drew from the results.

➜ The structure of the atomic cloud. ➜ How electrons can jump to higher levels.

19. State whether the following statements are true or false. Explain your answer based on today’s atomic model: a) The nucleus of the atom is neutral. b) Electrons orbit the nucleus at a high speed. c) An atom’s electron cloud is negatively charged. d) Electrons can position themselves at any distance from the nucleus. e) The number of protons in an atom is equal to the number of electrons, and so has a neutral charge.

Most went through the leaf and some deviated from their trajectory. Gold foil Source of alpha particles

Alpha particles

Gold atoms

Particle dectector

15. Briefly explain the similarities and differences between Thomson’s model, Rutherford’s model and Bohr’s model. Why were Thomson and Rutherford’s models disproved at the time?

20. Since the discovery of the three subatomic particles in an atom, advances in technology have allowed other, even smaller, particles to be discovered: bosons, quarks, positrons, neutrinos, etc.

16. State whether the following statements support Thomson’s model, Rutherford’s model or Bohr’s model, or more than one of them:

Find out more information about these types of particles and create a datasheet, following your teacher’s instructions.

a) An atom is a compact sphere.

21. Listen and define the following terms in your notebook, based on what you have learnt in this section.

b) Electrons orbit at fixed distances. c) The nucleus is tiny compared to the atom. d) Electrons are embedded. e) An atom has a neutral charge. 17. Answer the following questions and explain why. a) What do we mean by an atom is mostly empty space? b) In Bohr’s atom, can an electron move to different levels? If so, how?

Thomson’s model.

Nucleus of an atom.

Rutherford’s model.

Atomic cloud.

Bohr’s model. 22. Draw a flow chart to summarise the contents of this section. Remember you can add the definitions or explanations from the previous exercise.

c) Why are atoms electrically neutral? 18. Describe today’s atomic model. Include the following important information: ➜ The parts of an atom. ➜ The particles found in each of them.

The layers of an atom.

The structure of matter. Groups of atoms

Atomic number and mass number of an atom Atoms are defined by the number of protons, neutrons and electrons they contain.

Litio-6

The atomic number (Z) is the number of protons in an atom’s nucleus. All atoms of the same chemical element have the same atomic number, and if the atom is neutral, the atomic number also tells us the number of electrons the atom contains. The mass number (A) is the total number of particles in the atom’s nucleus and is therefore the same as the total number of protons and neutrons the atom contains. The mass number is the atom’s mass expressed in atomic mass units (u).

6 3

Litio-7

5 What are isotopes?

7 3

Two atoms can have a different number of neutrons, even if they have the same atomic number, making them isotopes of the same element.

Isotopes of lithium.

Isotopes are atoms of the same chemical element with a different mass, because they have the same number protons but a different number of neutrons. Some isotopes are unstable and spontaneously disintegrate, emitting radiation and particles. This is called radioactivity.

6 How do atoms combine? Atoms rarely exist alone in nature. The links between atoms are called bonds. There are three types of bonds: ➜ Ionic bonding, which is the attraction of oppositely charged ions. Ions form when atoms lose or gain electrons. Ionic compounds are crystalline solids that are soluble in water. ➜ Covalent bonding, which involves the sharing of electrons to form neutral groups called molecules. Covalent compounds can be liquid or gas at room temperature and their properties vary.

Water ➝ H2O

➜ Metallic bonding, specific to metals, forming a crystal lattice of cations from the metal atoms, which loose one or several electrons. Those electrons can move freely among the structure of cations. Metals have a characteristic shine and are good electricity and heat conductors.

Na+

+ - Cl Cl - +Na + Na - Na - +Na + - Cl Cl Cl - +Na +Na + - Cl Cl Na Na - Cl Na Cl + + + Cl Cl - +Na - Cl - +Na + + - Cl +Na Cl Cl Na Na Cl - +Na - +Na - Na + - Cl + - Cl NaCl Cl - Cl +Na - +Na +Na + - Cl + - Cl Na+ - +Na - ClNa +Na Na - Cl - Cl + Na - Cl + + NaCl Na Cl - Cl - +Na - ClNa + - Cl + - Cl +Na - Cl Na+ - +Na - Cl - Cl - Cl Na+ - +Na + Na +Na - Cl Na Cl Cl Na Na Cl Na Cl Cl + + + + + Cl + + - Cl - Cl NaCl - + Na +Na + Na - Cl - +Na Na+ Cl - ClNa Na - ClNa Na+ + - Cl Cl+ - Cl - Cl + - Cl + Na +Na +Na Cl Na + Na Na Na - ClNa - Cl Cl + +Na + NaCl - Cl Cl + - Cl + Na - ClNa + - Cl +Na - + Na - Cl Na+ Cl - +Na Cl - ClNa - ClNa +Na Cl + + Cl Na - Na + + - Cl Cl - Cl Na + Na Cl - Na - +Na NaCl + - ClNa + Cl - +Na Na+ Cl - Na - ClNa + Cl Cl - Na + Cl +

Oxygen ➝ O2

Ionic bonding. 18

UNIT 2

Metal bonding.

Covalent bonding.

23. Answer the following questions:

29. Fill in the gaps:

a) If we know an atom’s atomic number but not its mass number, what information do we have?

a) An anion is a  with a  charge.

b. How is the atomic mass unit defined (u)? Consult chemistry books or the Internet and write a brief paragraph for your answer.

c) An ionic compound is formed by ions with a  sign, in other words, by  and by .

24. A atom’s atomic number is 21 and its mass number is 45. Given it is a neutral atom:

30. Hydrogen (H) and chlorine (Cl) are two elements that combine forming diatomic molecules of hydrogen chloride (HCl).

a) How many protons, neutrons and electrons does it have? b) Draw a diagram of the atom. c) Can you identify which element it is? You can consult the periodic table. 25. Atom A has atomic number 25 and mass number 52. Atom B has mass number 55 and its nucleus contains 30 neutrons. Indicate whether these statements are true or false: a) Both atoms have the same atomic number.

b) Ionic compounds are  in water.

Given that hydrogen only has one electron and an atom of chlorine has 17 electrons, draw a diagram of how the chlorine atom and hydrogen atom combine via covalent bonding.

31. Explain why we can say that metallic bonding falls between ionic and covalent bonding based on the characteristics of each one. 32. Which type of bonding would occur between each of the following substances based on their described properties?

b) Atom A has more neutrons than atom B. c) Atom A must have 25 electrons in its cloud.

Substance 1. It is a solid that is a good electricity conductor.

Mass number (A) (protons + neutrons)

Substance 2. It is a crystalline solid that is soluble in water.

Substance 3. It is a non-crystalline solid that is not soluble in water and does not conduct electricity.

Atomic number (Z) (protons) 26. Two atoms X and Y, contain 15 protons in their nuclei. Atom X has 20 electrons, and the mass of atom Y is 33 u. Indicate whether these statements are true or false:

33. Listen and define the following terms in your notebook based on what you have learnt in this section. Atomic number. Mass number.

a) Both atoms are isotopes.

Isotopes.

b) Both atoms belong to different chemical elements.

Ionic bonding.

c) Atom X has an atomic mass of 35 u.

Covalent bonding.

d) Atom Y has 33 neutrons.

Metallic bonding.

27. Answer the following questions: a) Why do bonds form between atoms? b) What type of bonds exist? 28. Sodium fluoride is a substance formed by cations Na and anions F–.

a) Explain which type of bonding takes place between the particles. b) Based on the above, what will the state of sodium fluoride be at room temperature?

1 1

Protium H (99,98 %)

Deuterium 2 1H (0,02 %)

3 1

Tritium H (inestable)

Isotops of hydrogen.

34. Draw a flow chart to summarise the contents of this section.

The structure of matter. Groups of atoms

UNIT

3 Elements and compounds. The periodic table

Iron mining in Andalusia Metals are much sought-after chemical elements due to their properties and wide range of applications. Out of all the metals, including those found in their native state in nature —like gold and silver— and those that are an essential component of modern technological devices —like lithium—, iron features prominently. Ironworking dates back to the 12th century BC, believed to have been discovered in the Middle East. It was so revolutionary that a whole period was named after it —the Iron Age—, with the introduction of new weapons and tools made from this metal and with far-reaching social and economic consequences. In groups and following instructions from your teacher, you will work on iron extraction and mining in Andalusia, from ancient times to the present day.

Explore 1 Iron is not found pure in nature; rather it is found in ores and minerals, which are

abundant and easy to extract. From your information sources, find out which are the most common iron-containing ores and minerals. 2 Choose two of the ores and minerals that you listed in the previous exercise.

Research them in more detail and prepare a data sheet for each, including their composition, the percentage of iron they contain and where the highest-producing deposits are found. 3 How is iron extracted from its ores and minerals? Explain the physical and chemical

processes involved in detail and give a specific example. 4 In Andalusia there have been large, highly productive iron ore mines since Roman

times. Some iron mines are even still active today. On the Internet look up information about El Cerro del Hierro (Seville) and the Alquife mines (Granada).

Elaborate 1 Based on your findings, prepare a presentation about iron and how it is extracted

in Andalusia. 2 Your presentation must include figures, interesting facts and pictures and you

must quote your sources.

Communicate 1 When you have finished your presentation, present it to the rest of the class. 2 End with a discussion about the importance of iron for different civilizations.

1 How are elements and compounds different? The present-day concept of a chemical element was first introduced by English chemist Robert Boyle in 1661. He defined a chemical element as a substance that cannot be broken down into simpler materials. An element is a pure substance from which no other different substances can be obtained by means of chemical processes. This is because it is formed by a single type of atoms (with the same atomic number, Z). A chemical compound is a pure substance formed by several types of atoms (with different atomic numbers). When subjected to chemical processes, a compound gives rise to different chemical elements. Just over one hundred chemical elements have been identified up to today. Their properties are very diverse, including their aggregate state, metallic character and chemical reactivity, resulting in an equally diverse range of technology applications.

Copper Noble and abundant metal. Good conductor of electricity.

Hydrogen Light and f lammable gas. Environmentallyfriendly fuel.

Applications of the ELEMENTS

Uranium Radioactive metal. Fuel in some nuclear plants.

Gold Silver Noble metals used in jewellery.

Titanium Light metal. Alloy component.

Sulphur Yellow solid. Synthesis of chemical products.

Helium Light and inert gas. Filling and gaseous mixtures.

Compounds and formulas The proportion of the atoms in a compound is expressed as a formula.

Methane gas

If the compound is formed by independent molecules, the formula indicates which and how many atoms form each molecule.

CH4

If it is an ionic network, the formula represents the proportion of atoms of each kind that form it. Therefore, the formula gives us both qualitative and quantitative information about the compound.

UNIT 3

When there is no subscript, we understand it to be 1.

The symbols indicate that the compound is formed by hydrogen (H) and carbon (C). Subscripts indicate that each molecule of methane (CH4) is formed by 1 carbon atom and 4 hydrogen atoms.

1. Explain whether the following statements are true or false, justifying your answer in each case: a) Any pure substance is an element. b) Elements are in a gaseous state. c) An element is formed by the same type of atoms. d) All elements appear combined in nature. e) A compound must contain at least two different elements. 2. Answer the following questions: a) What is the definition of a chemical element?

8. Briefly answer the following questions: a) What is the meaning of the formula of a chemical compound? b) What do the subscripts indicate? Give an example in each case. 9. The hydrogen peroxide molecule is formed by two hydrogen atoms and two oxygen atoms. a) What would its formula be? b) What similarities and differences are there between this compound and water?

b) Which method should we follow to find out if a given substance is an element or not? 3. Taking into account the concept of a chemical element, explain which of the following substances can be considered elements: a) Hydrogen gas: its molecule is formed by two hydrogen atoms being joined together (H2).

10. Interpret the formulas of the following compounds qualitatively and quantitatively:

b) Fluorite: mineral formed by a crystal structure of calcium cations and fluorine anions.

a) Sulphuric acid: H2SO4 b) Sodium carbonate: Na2CO3

c) Iron: metal formed by millions of iron atoms being joined together.

c) Potassium phosphate: K3PO4

d) Calcium carbonate: when heated at high temperature, it emits carbon dioxide and quicklime (calcium oxide). 4. Look up information in books or on the Internet and answer these questions: a) What is the most important element in all living beings? Why? b) Why do you think that this is also the most abundant element in oil, coal or natural gas? 5. Chlorine, silicon, mercury, chrome and argon are some chemical elements with important technology applications.

11. Listen and define the following terms in your notebook, based on what you have learnt in this section. Element. Compound. Formula. Symbols. Subscripts. 12. Draw a flow chart to summarise the contents of this section. Remember that you can add the definitions or explanations from the previous exercise.

Collect information from different sources and prepare a presentation with a slide for each element, including a title, its main properties, its most important uses and any helpful illustrations. 6. In recent years, there has been an increasing demand for lithium worldwide. Use books, current-affairs magazines or the Internet to find out how lithium is extracted and where it is mainly used. Now answer the following question: Is the significant commercial interest in this chemical element justified? 7. We know that there are just over one hundred chemical elements but millions of chemical compounds have been identified. How do you explain this?

Elements and compounds. The periodic table

2 How are the elements arranged in the periodic table? The chemical elements are classified according to different criteria. One of the ways of classifying them is into metals and nonmetals, on the basis of their properties. Metals have a characteristic shine, are ductile and malleable, have high melting points, with exceptions, and are good conductors of electricity and heat. In addition, they are hard and combine with nonmetals such as oxygen and sulphur. Nonmetals are fragile, opaque and dull, with low melting points. They are also soft, electrical and thermal insulators, and capable of bonding both with metals and with other nonmetals.

Alkali metals (Li, Na, K, Rb, Cs, Fr).

Metalloids have properties that are halfway between those of metals and nonmetals. Around 1868, Russian Dmitri Ivanovich Mendeleiev and German Julius Lothar Meyer independently devised an arrangement of the known elements in table form, after ordering them according to their atomic masses. When the proton was discovered, English physicist Henry Moseley proposed the use of the criterion of increasing order of their atomic numbers. The properties of the chemical elements are repeated periodically as they are arranged in increasing order of their atomic numbers. This fact is known as periodic law and it enables the arrangement of the elements in table form, in groups or columns and periods or rows.

There are 18 groups or columns which are correlatively 2 6 5 3 4 1 numbered from left to right. 1

2 1

Ti 40

C 14

O 16

18 He 17 Cl Ar 10

36 B 30 C 31 N 32 O 33 F 34 Ne 35 Zn Ga Ge As Se Br Kr

54 Al 48 Si 49 P 50 S 51 Cl 52 Ar 53 I Ag Cd In Sn Sb Te Xe

27 76

28 77

Nb Mo

22 57

23 72

24 73

86 V Ca Sc Ti Cr Mn Fe Co Ni Cu 78 Zn 79 Ga 80 Ge 81 As 82 Se 83 Br 84 Kr 85 Pt Au Hg Tl Pb Bi Po At Rn Cs Ba La Hf Ta W Re Os Ir 56

20 6

117 118 Sr 87 Y 88 Zr 89 Nb104 Mo105 Tc106 Ru107 Rh108 Pd109 Ag110 Cd111 In112 Sn113 Sb114 Te115 I 116 Xe Some properties of the atoms vary Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og

104

105

LANTHANIDES

Ce 90

ACTINIDES

Na Mg 5 Rb

37 5

12 37

19 4

Na Mg

Li 4 Be K 11

3 2

Elements of the same group or family have similar chemical properties; this means that they form similar 12 10 16 14 15 17 11 13 18 8 9 compounds and are involved in the same chemical 2 processes. He

gradually vary along a period, from left to 85 86 77 81 82 83 84 80 79 There75are 776periods or78rows, Pt Au Hg Tl Pb Bi Po At Rn Re Os Ir right. Atomic mass increases and atom numbered from top to bottom. size decreases, although there are some 108 111 112 107 109 110 113 114 115 117 118 106 116 Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og exceptions. 74

Pm Sm

Nd 92

Pm Sm

Pu Am Cm Bk

Es 68

Tm Yb

101

102

103

Fm Md No

100

Tm Yb

Lanthanides and actinides are kept outside the main body for the sake of convenience.

Among the 9018 groups of93 the94 periodic alkaline metals (group 1), halogens 95 99 101 91 96 table, 98 103 100 92 97 102 Np Pu(group Am Cm U gases Cf particular Es Fm Md No Lr (group 17)Th andPanoble 18) Bk are of importance. Noble gases have the most stable electron configuration because they either have completely filled shells or have 8 electrons in their outermost shell. 24

UNIT 3

13. Write three properties that clearly distinguish metals from nonmetals.

18. Look at the picture below. It explains how two properties of the chemical elements vary: metallic character and atomic size. PERIOD

GROUP

2 1 Increases

Na Mg

Metal.

14. True or false? Correct any false statements. a) The elements in a period have the same outer electron configuration. b) Alkaline metals are highly reactive. c) The elements of group 1 form cations with a charge of +2. 15. Which element is it? Search for it in the periodic table. a) It is a noble gas from the third period. b) It is a liquid halogen at room temperature. c) It is the lightest alkaline metal. d) It is a transition metal that belongs to group 6 and to the sixth period. 16. Look at the periodic table, and answer these questions: a) How many nonmetals are there? b) Which elements form the third period? And group 11? c) How many elements does the sixth period contain? d) In which group and period can we find caesium (Cs)? 17. Using the periodic table, indicate: a) The name and symbol of three metalloids. b) The name and symbol of two lanthanides. c) What type of element are phosphorus and chlorine? d) Which element has atomic number 42 and where can we find it?

18 2

Nonmetal.

Decreases

Nb Mo

104

105

106

108

109

110

111

112

113

114

115

Tm Yb

107

Pm Sm

Variation in metallic character and atomic size. Ce

116

Ne 17

Variation in metallic character and atomic size.

Br 53

Ar 36

Kr 54

Xe 85

117

118

a) According to the figure, which is the biggest atom: silicon Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr or chlorine? 90

100

101

102

103

b) Carbon is a nonmetal, while silicon is a metalloid and lead is a metal. Think about whether this is in keeping with what the picture shows. c) Use the figure to compare the atomic size and metallic character of rubidium and cobalt. 19. As you know, silver is a metal, sulphur is a nonmetal and silicon is a metalloid. Find information in books or on the Internet and use it to prepare a datasheet for each of these three elements. The datasheets must mention the properties that cause each element to be classified as metal, nonmetal and metalloid, respectively, according to the qualitative and quantitative information that you have gathered. 20. When we go down a group of the periodic table, the size of the atoms increases. How can we explain this fact, taking into account the way the shells are filled with electrons? 21. Listen and define the following terms in your notebook, based on what you have learnt in this section. Metals. Nonmetals. Periodic law. Periodic table. Group (of the periodic table). Period (of the periodic table).

Halogen metals (F, Cl, Br, I, At, Ts)

22. Draw a flow chart to summarise the contents of this section. Remember that you can add the definitions or explanations from the previous exercise.

Elements and compounds. The periodic table

3 What is a mole? There is one crucial concept in chemistry: amount of substance. It is one of the base quantities of the International System and represents the number of particles that make up an amount of substance, which is known as Avogadro’s number. The mole is the unit for amount of substance in the International System. A mole is equivalent to a number of particles equal to 6.022 · 1023 (Avogadro’s number). 1 mole = 6.022 · 1023 particles

Water is formed by molecules of H2O. Each mole of water contains 6.022 ∙ 1023 molecules.

Copper is a metal formed by atoms of this element. Each mole of copper contains 6.022 ∙ 1023 atoms.

To calculate the number of moles related to a certain number of particles or vice versa, it is sufficient to apply the proportionality ratios, where one mole contains an Avogadro’s number (6.022 · 1023) of particles. The particles that the mole represents can be atoms or molecules. The mass of an atom is its atomic mass, which coincides with its mass number (A). A molecule’s mass is called molecular mass; we calculate it from the molecular formula, adding together the masses of its elements.

4 What is molar mass? The molar mass is used to show the ratio between the amount of substance (in moles) and the mass (in grams) when dealing with macroscopic quantities. Molar mass (M) is the mass of a substance, expressed in grams, which contains 6.022 · 1023 particles that make up said substance, in other words, 1 mole. Its value coincides with the molecular mass value and its unit is g/mol. Since the molar mass corresponds to the mass of one mole, the ratio between the number of moles (n) and the mass in grams (m) of any amount of substance is established through its molar mass (M).

Number of moles =

UNIT 3

Mass (g) Molar mass (g/mol)

→n=

m M

Carbon dioxide (CO2) The atomic mass of each element: atomic mass of C = 12 u atomic mass of O = 16 u The molecular mass of CO2 is: M (CO2) = 1 · 12 u + 2 · 16 u = 44 u

23. Using the definition of mole, calculate:

28. A container holds 0.35 moles of butane gas (C4H10).

a) The number of particles that are equivalent to 6 moles. b) The moles that are equivalent to 2.7099 · 10 particles. 24

c) The particles contained in 0.3 moles. d) The moles that are equivalent to 3.011 · 1023 particles. e) The number of particles in 2.6 moles. 24. Consult the periodic table for the necessary atomic mass values, and calculate the molecular mass or the formula mass of the following chemical compounds: a) Nitric acid (HNO3). b) Acetone (C3H6O). c) Sodium phosphate (Na3PO4). 25. Indicate whether the following statements are true or false. Explain your answer. a) One mole of hydrogen atoms has a lower mass than one mole of oxygen atoms. b) Molar mass and molecular mass are represented by the same number, although they are different quantities. c) Molar mass is the same for all substances because it is the mass of an Avogadro’s number of particles. d) To define molar mass, the substance must be formed by molecules. 26. One bottle of oxygen contains 935 g of this gas. If the formula for elemental oxygen is O2: a) How many moles of oxygen are there in the bottle? b) How many molecules are there in the bottle?

a) Using the definition of mole, calculate how many molecules of butane the container holds. b) Find out how many atoms of carbon and hydrogen there are in the container. c) Find out the molecular mass of butane. d) How many grams of butane are equivalent to the 0.35 moles of butane? 29. Manganese dioxide, the main component in pyrolusite, a mineral that is used as ore to extract metallic manganese, is a compound formed by one atom of manganese and two of oxygen. a) Write the formula of this compound and calculate its molecular mass (consult the periodic table). b) Calculate the number of moles of manganese dioxide in 110 g of this compound. c) How many manganese atoms are there in that amount of the compound? 30. Sucrose is the sugar we normally eat, often adding it to our beverages. Research its formula and answer the following: a) Calculate the molecular mass of sucrose. b) Look up the equivalence between the atomic mass unit and the kilogram in books or on the Internet, and express the mass of this molecule in g. c) How many molecules of sucrose are there in a 1 kg packet of sugar?

c) How many atoms does it contain? 27. Calculate the number of moles and particles contained in the following amounts of each substance: a) 0.54 g of water (H2O). b) 5.5 g of beryllium dihydride (BeH2). c) 225 g of gaseous nitrogen (N2). d) 45 mg of carbon monoxide (CO). Sucrose.

31. Listen and define the following terms in your notebook, based on what you have learnt in this section. Amount of substance.

Molecular mass.

Mole.

Molar mass.

Avogadro’s number. 32. Draw a flow chart to summarise the content of this section. H2O.

Remember that you can add the definitions or explanations from the previous exercise.

Elements and compounds. The periodic table

Evaluate UNITS 1, 2, 3

Copy the following sentences in your notebook, Then, write the missing words. 1. It is the phase of the scientific method in which the phenomenon under study is reproduced under controlled conditions to check whether the hypothesis is valid or not. The 2. They are properties that can be measured in common matter, on which the rest of the properties are based.

3. It is the place designed to conduct scientific work and which is equipped with the necessary instruments and safety measures. The 4. It is the subatomic particle that has no electrical charge and it has the same mass as the proton. The 5. They are two atoms that have the same atomic numbers but a different mass.

6. It is the type of bond that is formed when two atoms combine, one with a tendency to gain electrons and another with a tendency to lose electrons.

Scientific report.

7. It is the International System unit of matter that is based on Avogadro’s number. The 8. They are the columns of the periodic table formed by elements that share the same chemical properties. or 9. It is the quantity that tells us the mass of a substance, equal to one mole of that substance.

10. It is a phenomenon that happens when the nuclei of atoms are unstable and disintegrate, producing other chemical elements.

Evaluate

Write the correct answer in your notebook. There is only one possible answer! 1. The main phases of the scientific method are: A

Observing and measuring.

Formulating mathematical laws.

Formulating hypotheses and experimenting.

2. Which are basic quantities in the International System of units? A

Length, mass and force.

Temperature, amount of matter and time.

Velocity, current and mass.

3. Which units are submultiples of the basic unit of length? A

Decimetre, metre and hectometre.

Nanometre, centimetre and kilometre.

Centimetre, millimetre and micrometre.

4. Which of the following speeds is more than 90 km/h? A

25 m/s.

1,500 cm/s.

30 m/s.

5. Which laboratory material is not made of glass? A

A pipette.

A volumetric flask.

A wash bottle.

6. Which of the following instruments measures a derived quantity? A

A stopwatch.

A pan balance.

A test tube.

7. Which subatomic particle is the lightest and has a charge of –1.602 ∙ 10–19 C?

9. Why do atoms form different types of bonds? A

They gain stability.

There is a mutual electrical attraction between them.

They tend to share pairs of electrons.

10. Which bond is formed when neutral atoms share electrons? A

Ionic bond.

Covalent bond.

Metallic bond.

11. Which of the following properties does not apply to metals? A

They are electrical insulators.

They are shiny.

They combine with nonmetals.

12. Elements are sorted in the current periodic table in order of: A

Increasing atomic mass.

Increasing atomic number.

Increasing atomic size.

13. Which of the following statements is correct for a compound with the formula Na3PO4. A

Its molar mass is 164 u.

It contains more than 40% by mass of oxygen.

One mole of it has a mass of 164 g.

14. Based on the definition of a mole, 4,8184 ∙ 1024 particles are equivalent to: A

7 moles.

8 moles.

9 moles.

15. For a substance with a molar mass of 54 g/mol, we can say that:

Proton.

Its molecular mass is also 54 g/mol.

Electron.

5 moles of the substance are equivalent to 270 g.

Neutron.

Without the formula we cannot calculate its molecular mass.

8. Bohr’s model included a hypothesis that is still upheld in today’s model. What is it?

16. What does a 1 L bottle of water with a density of 1 g/cm3 contain?

An atom is mostly empty space.

The nucleus contains neutrons and is heavier.

Less than 50 moles of water.

The electrons are arranged in levels in concentric circles.

1025 molecules of water.

Neither answer is correct.

Evaluate

PRACTISE IN ENGLISH Can you drink distilled water? Chemistry teachers warn us to ‘never drink distilled water’. They warn that having a drink from the wash bottle would lead to a horrid death, with gastric haemorrhages and ruptured cells. However, we have a neighbour who is generally aware of health matters, but never went to chemistry classes. He just bought a distiller and swears the water with no salts ‘detoxifies’ him. So? It is true that cells could rupture due to osmosis, since cell membranes are semipermeable. Only water can get through, not salts or sugars, which are too big to be transported through the pores of the cell membranes. However, water can enter the cell, equalising the concentration of salts and sugars inside the cell with the concentration outside the cell. When the concentration gradient is high, so much water enters the cell that it cannot hold it in anymore and the cell explodes.

The same is true for blood cells, but you would have to be given distilled water intravenously. However, the consequences of drinking distilled water are actually not that serious - far from it. Your stomach acids and the food you have eaten cause the pure water to react chemically with mineral substances, so your cells do not actually come in contact with pure water. As such, tea or coffee made with distilled water poses no danger. Some people even say they are quite good for you. Some people even believe distilled water is good for you, since it contains no harmful substances like lead, nitrates and pesticides. So, in theory, distilled water should detoxify you. However, the German Nutrition Society and scientists warn against using only distilled water. Consuming distilled water, especially when combined with an unbalanced diet, eventually deprives your cells of potassium and sodium ions, which alters your balance of electrolytes. Translated from www.investigacionyciencia.es, Alexandra Schulmeister

Think about it Answer the following questions based on the text. Why do cells rupture in distilled water? Nevertheless, why would ingesting distilled water not be dangerous? What is the argument of the people who support drinking distilled water to improve their health?

Discuss your conclusions Hold an idea-sharing session with your classmates on the importance of diet based on scientific evidence.

Practise in English

Is there anywhere more radioactive than Chernobyl? If you have seen the HBO series that tells the Chernobyl story from minute zero, you know the roof of the nuclear plant became the most dangerous place on Earth due to extreme radiation. Just two minutes of exposure could reduce a person’s life expectancy by 50 %. Over the years, the danger has decreased considerably. Although there is still a restricted area covering about 1,600 square meters, people can go on tours of nearby towns that were abandoned after the accident. Empty courtyards, derelict amusement parks, ruined school classrooms… it is a ghost town. So, is there anywhere with higher radiation levels, anywhere more dangerous? Apparently, there is, and it’s in the Pacific Ocean. According to a recent Columbia University study, some parts of the Marshall Islands could be the most radioactive places in the world. If you are not sure where these islands are, this is the place where the United States conducted 67 nuclear tests during the Second World War. Researchers detected elevated levels of radioactive elements like americium, caesium and two types of Plutonium-238 in different soil samples taken from 11 different islands. The highest levels were found on Bikini Island, where the United States conducted the largest hydrogen bomb test in history. All the elements mentioned above were also released in the Chernobyl accident. More than 30 people were directly affected by them and died within the week from acute radiation sickness. Despite that low figure, tens of thousands are believed to have been indirectly affected for years. Researchers testing for Americium-241 found that certain islands contained much higher levels of the isotope than those found in Chernobyl in 2009. They also showed that Bikini Island had up to 1,000 times more plutonium than Chernobyl or Fukushima (the Japanese power plant where a nuclear disaster was caused by an earthquake in 2011). Translated from www.quo.es, Alberto Pascual

Think about it Answer the following questions based on the text. The Chernobyl nuclear accident happened in 1986. So, why is there still a danger from radioactivity in the area? If a major radioactive leak occurs somewhere, why should the people who live there be evacuated immediately? Why is the presence of radioactive isotopes in the Marshall Islands higher than at Chernobyl?

Discuss your conclusions Nuclear power plants generate a large part of the electric power required in developed countries despite the risk they pose. Discuss whether you think this is a risk we should take as a society.

Practise in English

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