Read GCSE SCIENCE text version


Dr. E. Kruiswijk, 2005.


First published 2005 Copyright © 2005 Elbertus Kruiswijk Published by The Chemical Bookstore, All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. NOTICE: The author of this book has taken care that the information contained herein is accurate and compatible with the standards generally accepted at the time of publication. Nevertheless, it is difficult to ensure that all the information given is entirely accurate for all circumstances. The publisher and author do not guarantee the contents of this book and disclaim liability, loss, or damage incurred as a consequence, directly or indirectly, of the use and application of any of the contents of this book. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe.


HOW TO USE THIS GUIDE This revision exercise booklet is designed to help you prepare for your GCSE exam (Double and Triple award) in Chemistry. It is not meant to replace your class notes but it should be very useful for a "final revision" before the exam. Not everything covered in your course, is covered in this revision guide. I recommend that you buy a revision guide from Letts, Lonsdale, WHSmith, or BBC bitesize to name a few. Your teacher can give you advice which one to buy.

ELEMENTS, COMPOUNDS AND MIXTURES ELEMENTS All substances are made up of ATOMS. An ELEMENT is a substance that CONTAINS ONLY ONE TYPE OF ATOM. Each element is represented by a SYMBOL and some of the common ones are shown in the table:

Element Symbol

Hydrogen H

Helium He

Carbon C

Oxygen O

Iron Fe

Copper Cu

There are about 100 elements and more than three-quarters are METALS. The rest of course are NON-METALS.

COMPARING METALS AND NON-METALS METALS Usually have HIGH melting and boiling points except group 1 and 2. Have SHINY surfaces Can be HAMMERED, BENT or STRECHTED into SHAPE Are GOOD CONDUCTORS of HEAT and ELECTRICITY Are POOR CONDUCTORS of HEAT and ELECTRICITY, except Graphite NON-METALS Usually have LOW melting and boiling points Are mostly DULL When solid are BRITTLE


Some exceptions: Metals Not all metals have these properties. For example, the alkali metals (Lithium, Sodium, and Potassium) are soft metals. They have low densities and have low melting points. Mercury (liquid) also has a low melting point for a metal.

Non-metals Carbon in the form of graphite is a good conductor of electricity. The only non-metal that conducts electricity (it has a free electron pair). Carbon in the form of diamond has a very high melting point.


COMPOUNDS AND MIXTURES Compounds are substances which contain two or more elements chemically joined together. They can be represented by a CHEMICAL FORMULA e.g. sodium chloride is NaCl. Mixtures contain two or more substances (elements or compounds) which are not chemically joined together and are usually easy to separate e.g. air is a mixture of lots of substances such as nitrogen, oxygen, carbon dioxide and water vapour.

ATOMIC STRUCTURE Atoms were once thought to be the smallest particles of matter but we now know that there are even smaller particles (quarks) inside atoms. Atoms contain a nucleus consisting of protons and neutrons and around this nucleus are shells of electrons. The relative masses and charges of the three particles are shown in the table:

Particle Proton Neutron Electron

Relative Mass 1 1 0

Relative Charge +1 0 -1

Atomic Number is the number of protons in the nucleus of an atom (it is also the number of electrons in a neutral atom)

Mass Number is the total number of protons and neutrons in the nucleus.

These numbers are shown on the element symbol as: Mass Number 56 e.g. 26 Fe


Atomic Number


If you want to work out the number of neutrons you subtract the atomic number from the mass number. So how many neutrons does iron have?

Electron arrangement - the electrons orbit the nucleus in SHELLS. The first shell nearest the nucleus can hold up to TWO electrons, the second EIGHT, the third also EIGHT and any remaining go into the fourth shell e.g. sodium has atomic number 11 so has 11 electrons arranged 2.8.1

BONDING BETWEEN ATOMS When atoms bond together the arrangement of the outer shell electrons changes. Each atom wants to FILL its outer shell to become STABLE. There are TWO ways of doing this:


· By TRANSFERRING electrons from a METAL atom to a NON-METAL atom e.g. sodium and chlorine forming sodium chloride:

The metal atom LOSES an electron and becomes a POSITIVE ION. The non-metal atom GAINS an electron and becomes a NEGATIVE ION. Millions of ions are held together STRONGLY, in a crystal, by IONIC BONDS so such compounds have HIGH MELTING POINTS. They also dissolve in water and are GOOD CONDUCTORS of electricity when DISSOLVED or MELTED. Examples include NaCl, MgCl2 and CaCO3.

· By SHARING electrons between two NON-METAL atoms to produce COVALENT compounds e.g. CH4.


There are three ways to show the covalent bonding in a compound. The three-ways for chlorine is shown below.

Covalent bonds, like ionic, are STRONG but most covalent compounds are small MOLECULES with weak attractions between these molecules. This means they have LOW MELTING and BOILING POINTS. There are no charged particles present so they don't conduct electricity. Examples include O2, Cl2, CH4 and NH3. Some covalent substances have GIANT STRUCTURES and they have HIGH MELTING POINTS because STRONG COVALENT BONDS have to be broken. Examples include diamond and graphite.


Practice questions 1. Complete the following table. Element Number of protons C 12Mg 23 Na 16 O 37 Cl 20Ca 13Al

1H 12

Number of neutrons 0

Number of electrons

Electron arrangement

6 12 12 8 2.8.7 20 14

12 6C.

From the table we can write the full symbol of carbon as of (a) H (b) Na (c) Ca

In the same way give the symbol


2. The electron arrangement of chlorine is 2.8.7. Draw a diagram showing this, using circles to represent the shells and crosses (x) to represent the electrons.

3. Fill in the spaces in the following: Elements bond together to form ________________. When they do this the atoms of each element try to _____________ their outer electron shells to become more _______. There are two types of chemical bond ionic and covalent.

An ionic bond forms between a metal and a ____________. An ______ of electrons takes place. The metal atom loses its outer electron and becomes a ______. The non-metal atom gains this electron and becomes a _______ charged ion. A covalent bond forms between two ________ atoms. This involves ________ of electrons. Both ionic and covalent bonds are very ________. 4. Complete the following table: Property Type of bonding Melting point (high or low) Electrical conductivity when solid Electrical conductivity when dissolved or molten Solubility in water Sodium Chloride Candle wax


CHEMICAL REACTIONS AND EQUATIONS 1. In a chemical reaction REACTANTS are changed into PRODUCTS.

2. A WORD EQUATION has the names of the reactants on the left hand side and the names of the products on the right hand side. An arrow or an equal sign separates the reactants from the products, e.g. hydrogen + oxygen water

3. A CHEMICAL EQUATION replaces the words by chemical symbols and formulae. It is vital that the formulae are correct or the equation will be impossible to BALANCE,

e.g. 2 H2 + O2

2 H2O

4. When balancing an equation don't be tempted to change a formula to help you. The only way to balance the number of atoms on each side is by putting big numbers in front of the formulae.

5. If asked to write a chemical equation look to see if any formulae are given in the question. This will make your task much easier. Note however that you are expected to know the formulae of simple substances. The table below lists the more important ones (see how many you can fill in): NAME Water Carbon dioxide H2 Hydrochloric acid H2SO4 NH3 Sodium chloride NaOH CaCO3 MgO Oxygen FORMULA


6. State symbols may be used after formulae to show if the substance is solid (s), liquid (l), gas (g) or in aqueous solution (aq).

e.g. 2 Mg(s) + O2(g)

2 MgO(s)

THE PERIODIC TABLE The first Periodic Table arranged the elements in order of increasing atomic mass but we now arrange them in order of INCREASING ATOMIC NUMBER. A PERIOD is a HORIZONTAL ROW of elements. Elements in the same period have the same number of shells containing electrons e.g. Period 3 elements have 3 shells of electrons.

A GROUP is a VERTICAL COLUMN of elements. Elements in the SAME GROUP have SIMILAR CHEMICAL PROPERTIES since they have the SAME NUMBER OF ELECTRONS IN THEIR OUTER SHELL. The number of electrons in the outer shell is also the GROUP NUMBER e.g. Group 2 elements have 2 electrons in their outer shell. The transition metals do not have a group number, due to their multi-valency.

ALKALI METALS The alkali metals are Group 1 of the Periodic Table. They all react similarly as they all have 1 electron in their outer shell but they get more reactive as we go down the group. For example they all react with cold water to form a METAL HYDROXIDE and HYDROGEN but lithium does it less violently than sodium and doesn't melt to a silvery ball. Potassium gets so hot that the hydrogen gas ignites and a LILAC flame is seen. The metal hydroxide formed each time dissolves in water and turns it ALKALINE. This is why Group 1 metals are called the ALKALI METALS:

e.g. Sodium + water -> sodium hydroxide + hydrogen

(Note: Hydrogen gas is tested for with a LIGHTED SPLINT - it burns with a squeaky POP.)


The alkali metals are unusual among metals in that they have LOW MELTING POINTS and LOW DENSITIES (they float on water).

HALOGENS The halogens are NON-METALS in Group 7 of the Periodic Table. Typical of non-metals they all have low melting and boiling points. As we go down the group their melting and boiling points increase. CHLORINE is a GREEN GAS, BROMINE is a RED LIQUID and IODINE is a DARKGREY SOLID. They all exist as pairs of atoms (diatomic) e.g. Cl2, and they all form coloured vapours. Unlike the alkali metals which get more reactive going down the group they get less reactive going down. This is not surprising since metals and non-metals tend to be opposite. A more reactive halogen can displace a less reactive halogen from aqueous solutions of its salts.

e.g. Chlorine + Sodium Bromide -> Bromine + Sodium Chloride

Chlorine is the most important halogen and is used as a bleach and for killing germs in water and swimming pools.

NOBLE GASES These are in Group 0 also called Group 8 since they have 8 electrons in their outer shell. They are very UNREACTTVE since they don't need to gain or lose electrons to fill their outer shell. They exist as individual atoms unlike most gases which tend to have the atoms in pairs. Because of its INERT (unreactive) nature ARGON is used in LIGHT BULBS to stop the filament from burning out. HELIUM is very light and is used in WEATHER BALLOONS. It is preferred to hydrogen because hydrogen is explosive.

TRANSITION ELEMENTS The Transition Elements occur in the middle section of the Periodic Table between Groups 2 and 3. They are all METALS with HIGH MELTING POINTS and HIGH DENSITIES. They are typical metals and are hard, tough and strong. They are good conductors of heat and


electricity and can be bent or hammered into shape. They are much less reactive than Group 1 metals and do not react with oxygen or cold water (or if they do it is very slow e.g. iron rusting). They are used as CATALYSTS (substances that speed up reactions without being used up) e.g. iron and platinum. Their compounds are COLOURED e.g. COPPER compounds are BLUE or GREEN. Copper metal is used for ELECTRICAL WIRING because it is a GOOD CONDUCTOR. It is also used for domestic hot water pipes as it doesn't rust or react with water. Iron is made into STEEL, the most useful structural material of all e.g. it is used to build cars and bridges.

Practice questions 1. The Periodic Table arranges the elements in order of increasing _________ ________. The vertical columns are called ______ and the elements in these columns have similar ________ properties because they have the same _______ of ________ in their ______ _____. This number is also the group number e.g. group 1 elements have ______ electron in their ______ ________. The horizontal rows are called ________ and elements in the

same period have the same number of _________. Most of the elements are metals and they are found on the _______ side of the table.

2. The elements in Group 1 of the table are known as the _________. They have __________ densities and include metals like sodium and potassium. This is why they ___________ on water. Their reaction with water is vigorous producing the metal ________ and _______ gas. This can be tested with a __________ splint and it ______. The solution left is ________ and turns pH paper _________. The reaction gives out a lot of heat i.e. it is very ________. The metal _________ into a silvery ball and sometimes causes the fire e.g. potassium burns with a _________ flame. _______ gas to catch

3. The elements in Group 7 of the table are called _______. They are non-metals with _______ melting and boiling points. Chlorine is a ______ _____ at room temperature and bromine is a ______ ________. They are ____ conductors of _______ and _________.


They are diatomic molecules which mean they contain a pair of atoms _______ bonded together. They react easily with metals to form _________ compounds called _________. They also react with non-metals but the bonding is now _________. A reactive halogen can displace a _______ reactive halogen from a solution of its salt.

4. The elements in Group 0 of the table are known as the _________ gases. They are all chemically __________ because they have ______ ________ not molecules like other gaseous elements. shells of electrons. They exist as _______ is used as an inert gas in

light bulbs to prevent the filament from ________. The first element in the group, helium, is much ____ dense than air and is used in weather ________.

5. In the centre of the Periodic Table is a block of metallic elements, which include iron and copper, known as the _______ ________. Compared with Group 1 they have much ______ melting points. They are harder and stronger and much ________ reactive chemically. Their reactions with oxygen and water are much_________. Their properties make them very useful for certain things e.g. _______ is used to make steel (a very important structural material) and ______ is used for electrical wiring. The compounds of these elements are often coloured e.g. copper compounds are either ______ or _______.

6. Use the Periodic Table section to answer the questions that follow: Which element(s) up to bromine 1. has the largest atomic number? 2. are metals? 3. has two electrons in its outer shell? 4. is in the same group as sodium? 5. are in the same period as sodium? 6. are noble gases? 7. are alkali metals? 8. has similar chemical properties to fluorine?


9. are transition metals? 10. is the lightest? 11. has the electron arrangement 2.4? 12. are used to make steel? 13. is the least reactive? 14. How are sodium and potassium stored? Why is this? 15. Give one way that the alkali metals are typical of metals and one way that they are not? Hard Water (Triple award only)

Disadvantages of hard water

Advantages of hard water

It is more difficult to form a lather Some people prefer the taste. with soap. Scum may form in a reaction with Calcium ions in the water are good soap, wasting the soap. for children's teeth and bones. Limescale (a hard crust) forms It helps to reduce heart disease. inside kettles. This wastes energy whenever you boil a kettle. Hot water pipes 'fur up'. Limescale Some brewers prefer using hard starts to coat the inside of the water for making beer. pipes which can eventually get blocked up. A coating of limescale inside copper pipes, or especially old lead pipes, stops poisonous salts dissolving into water.

Hard water contains calcium ions, Ca2+(aq), or magnesium ions, Mg2+(aq). These ions react with soap, making it difficult to form a lather and producing scum. Hard water can be softened by adding washing soda (sodium carbonate) which removes the calcium ions in a precipitation reaction. Alternatively, the hard water can be passed through an ion-exchange resin in a


column. Sodium ions replace the calcium ions in the water as it passes through the column. Temporary hardness can be removed by boiling the water. The calcium hydrogencarbonate dissolved in the water breaks down when heated and forms limescale.

Practice Questions 1. Which of the following ions causes hardness in water? O Calcium ions O Sodium ions O Magnesium ions O Potassium ions

2. Which gas dissolves in rainwater, making it slightly acidic? O Oxygen O Nitrogen O Carbon dioxide

3. Complete this word equation: calcium carbonate + carbonic acid

4. Complete this sentence: The coating on the heating element inside kettles in areas with hard water is called ____________.

5. Complete this sentence: Scum forms in hard water when _________ reacts with calcium ions.


6. Hard water can be softened by adding washing soda (sodium carbonate). What type of reaction takes place? O Neutralization O Oxidation O Precipitation O Reduction

7. Which one of the following ions takes the place of calcium ions in hard water when it passes through an ion-exchange column? O Magnesium ions O Iron(lll) ions O Zinc ions O Sodium ions

8. Which compound causes temporary hardness in water? O Calcium hydrogencarbonate O Calcium sulphate O Magnesium sulphate

9. Which of the following methods will remove both temporary and permanent hardness from water? O Add washing soda O Boil the hard water O Pass through an ion-exchange column

The Manufacture of Sulphuric Acid (Triple award only) Sulphuric acid is manufactured in the Contact process. First, sulphur is burned in air to give sulphur dioxide. Then sulphur dioxide is mixed with more air to yield sulphur trioxide in a reversible reaction. A compromise temperature of 450 °C is chosen to speed up the reaction.


The gases pass through layers of vanadium(V) oxide catalyst which also increase the rate of reaction. Finally, sulphur trioxide is mixed with a mixture of 98 per cent solution of sulphuric acid to form an even more concentrated form of sulphuric acid (99.5 per cent).

Practice Questions 1. What is the formula of sulphuric acid? O HSO3 O HSO4 O H2SO4 O H2S

2. Which element is burned in the first stage of the manufacture of sulphuric acid? O Hydrogen O Sulphur O Vanadium


3. What is the name of the catalyst used in the Contact process? O Iron O Iron(lll) oxide O Vanadium(V) oxide

4. What temperature is chosen for the Contact process? O 150°C O 250 °C O 350 °C O 450 °C O 550 °C

5. Insert the same number in both boxes to balance the equation below. : ___O2(g) ____ SO3(g)

__ SO2(g) +

6. In the Contact process, the final stage involves dissolving the sulphur trioxide in ... O pure water. O 98 per cent sulphuric acid solution. O vanadium(V) oxide.

7. Does the catalyst used in the Contact process increase the percentage of sulphur trioxide formed? O Yes O No

8. Explain the temperature used in the Contact process.




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