GCSE SCIENCE REVISION
CHEMISTRY (P2)
OK it’s time to stop faffin about and get stuck in to some revision. If you want to do well in your science GCSE you will need to know all of the stuff on this revision booklet.
SECTION C2.1
You should know and / or be able to use / do the following
To represent the electronic structure of the first twenty elements ofthe periodic table in the following forms:
for sodium (and 2,8,1)
To represent the electronic structure of the ions in sodium, chloride, magnesium oxide and calcium chloride in the followingforms:
for sodium ion (Na+)and [2,8]+
To represent the covalent bonds in molecules such as water,ammonia, hydrogen, hydrogen chloride, chlorine, methane andoxygen and in giant structures such as diamond and silicondioxide in the following forms:
To represent the bonding in metals in the following form:
To write balanced chemical equations for reactions.
Atoms have a small central nucleus made up of protons andneutrons around which there are electrons.
The relative electrical charges are as shown:
Name of particle Charge
Proton +1
Neutron 0
Electron .1
In an atom, the number of electrons is equal to the number ofprotons in the nucleus. Atoms have no overall electrical charge.
All atoms of a particular element have the same number ofprotons. Atoms of different elements have different numbers ofprotons.
The number of protons in an atom is called its atomic number(proton number).
Atoms are arranged in the modern periodictable in order of their atomic number (proton number).
Electrons occupy particular energy levels. Each electron in anatom is at a particular energy level (in a particular shell). Theelectrons in an atom occupy the lowest available energy levels (innermost available shells).
Elements in the same group in the periodic table have the samenumber of electrons in the highest energy levels (outer electrons).
Compounds are substances in which atoms of two, or more,elements are not just mixed together but chemically combined.
Chemical bonding involves either transferring or sharing electronsin the highest occupied energy levels (shells) of atoms.
When atoms form chemical bonds by transferring electrons, theyform ions. Atoms that lose electrons become positively chargedions. Atoms that gain electrons become negatively charged ions.Ions have the electronic structure of a noble gas (Group 0).
The elements in Group 1 of the periodic table, the alkali metals,have similar chemical properties. They all react with non-metalelements to form ionic compounds in which the metal ion has asingle positive charge.
The elements in Group 7 of the periodic table, the halogens, havesimilar chemical properties. They react with the alkali metals toform ionic compounds in which the halide ions have a singlenegative charge.
An ionic compound is a giant structure of ions. Ionic compoundsare held together by strong forces of attraction betweenoppositely charged ions. These forces act in all directions in thelattice and this is called ionic bonding.
When atoms share pairs of electrons, they form covalent bonds.These bonds between atoms are strong. Some covalently bondedsubstances consist of simple molecules such as H2, Cl2, O2, HCl,H2O and CH4.
Others have giant covalent structures(macromolecules), such as diamond and silicon dioxide.
Metals consist of giant structures of atoms arranged in a regular pattern. The electrons in the highest occupied energy levels (outershell) of metal atoms are delocalised and so free to move throughthe whole structure. This corresponds to a structure of positiveions with electrons between the ions holding them together by
strong electrostatic attractions.
Now try these exam style questions
Structures and bonding
1The diagram represents an atom of an element.
(a)Write the electronic structure of this atom as numbers and commas.
...... (1)
(b)How many protons are in the nucleus of this atom?
...... (1)
(c)Name the other particles that are in the nucleus.
...... (1)
(d)In which group of the periodic table is this element?
...... (1)
(e)Draw a similar diagram to show the ion formed by this atom in ionic compounds. Show the charge on the ion.
2Complete the missing information (a) to (f) in the table.
Atomic number / Symbol / Electronic structure of atom / Formula of ion / Electronic structure of ion9 / F / (a) / (b) / [2,8]–
11 / (c) / 2,8,1 / Na+ / (d)
(e) / S / 2,8,6 / S2– / (f)
(6)
3A hydrogen atom can be represented by the diagram:
(a)Draw a similar diagram to show the electrons in the outer shell of a chlorine atom.(1)
(b)Draw a dot and cross diagram to show the bonding in a molecule of hydrogen chloride.(2)
(c)Explain why hydrogen and chlorine form a single covalent bond.
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(d)Explain why silicon can form giant structures.
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4(a)Draw a dot and cross diagram to show the arrangement of electrons in a magnesium ion. Show the charge on the ion. (3)
(b)Draw a dot and cross diagram to show the arrangement of electrons in an oxide ion.(3)
(c)What is the formula of magnesium oxide?
...... (1)
5Berzelius (1779–1848) carried out experiments to discover the atomic mass of many elements.
He wrote about the fact that bodies combine in definite proportions and that led him to suggest the existence of a cause.
(a)Suggest an observation that Berzelius might have made.
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(b)Is what Berzelius wrote a prediction or a hypothesis? Explain your answer.
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(c)Berzelius gave oxygen the number 100 to represent its relative atomic mass. He then set out to compare the mass of other elements with oxygen. However, he could not measure these directly because they could not be turned into gases – the temperature needed was too high and he did not have the equipment to do this.
(i)Explain, in general terms, the problem he had.
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(ii)Use this example to explain the relationship between technology and science.
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6The diagram represents atoms of potassium in the solid metal.
(a)What is the electronic structure of a potassium atom?
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(b)Explain as fully as you can how the atoms are held together in solid potassium metal.
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...... (3)
SECTION C2.2
You should know and / or be able to use / do the following
Substances that have simple molecular, giant ionic and giant covalent structures
have very different properties. Ionic, covalent and metallic bonds are strong. The
forces between molecules are weaker, eg in carbon dioxide and iodine.Nanomaterials have new properties because of their very small size.
To relate the properties of substances to their uses
To suggest the type of structure of a substance given its properties
To evaluate developments and applications of new materials, egnanomaterials, ad smart materials.
Substances that consist of simple molecules are gases, liquids orsolids that have relatively low melting points and boiling points.
Substances that consist of simple molecules have only weak forcesbetween the molecules (intermolecular forces). It is theseintermolecular forces that are overcome, not the covalent bonds,when the substance melts or boils.
Substances that consist of simple molecules do not conductelectricity because the molecules do not have an overallelectric charge.
Ionic compounds have regular structures (giant ionic lattices) inwhich there are strong electrostatic forces in all directionsbetween oppositely charged ions. These compounds have highmelting points and high boiling points.
When melted or dissolved in water, ionic compounds conductelectricity because the ions are free to move and carry the current.
Atoms that share electrons can also form giant structures ormacromolecules. Diamond and graphite (forms of carbon) andsilicon dioxide (silica) are examples of giant covalent structures(lattices) of atoms. All the atoms in these structures are linked toother atoms by strong covalent bonds and so they have very high
melting points.
In diamond, each carbon atom forms four covalent bonds withother carbon atoms in a giant covalent structure, so diamond isvery hard.
In graphite, each carbon atom bonds to three others, forminglayers. The layers are free to slide over each other and so graphiteis soft and slippery.
In graphite, one electron from each carbon atom is delocalised.These delocalised electrons allow graphite to conduct heat andelectricity.
Metals conduct heat and electricity because of the delocalisedelectrons in their structures.
The layers of atoms in metals are able to slide over each other andso metals can be bent and shaped.
Nanoscience refers to structures that are 1-100 nm in size, of theorder of a few hundred atoms. Nanoparticles show differentproperties to the same materials in bulk and have a high surfacearea to volume ratio, which may lead to the development of newcomputers, new catalysts, new coatings, highly selective sensorsand stronger and lighter construction materials.
Structures and properties
1The table contains information about some substances.
Complete the missing information (a) to (g).
Melting point (C) / Boiling point (C) / Electrical conductivity when solid / Electrical conductivity when molten / Solubility in water / Type of bonding / Type of structure1660 / 3287 / (a) / good / insoluble / metallic / giant
–101 / –35 / poor / (b) / soluble / covalent / (c)
712 / 1418 / poor / good / soluble / (d) / giant
–25 / 144 / (e) / poor / insoluble / (f) / small molecules
1410 / 2355 / poor / poor / insoluble / covalent / (g)
2Quartz is a very hard mineral that is used as an abrasive. It is insoluble in water. It is a form of silica, SiO2. It can form large, attractive crystals that are transparent and can be used for jewellery. It melts at 1610C. It does not conduct electricity when solid or when molten. It is used in the form of sand in the building and glass-making industries.
(a)Give three pieces of evidence from the passage that tell you that quartz has a giant structure.
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(b)What type of bonding is in quartz? Explain your answer.
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3Copper can be used to make electrical wires, water pipes, and cooking pans.
(a)Suggest three reasons why copper is used to make cooking pans.
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(b)Which two properties of copper depend on the ability of delocalised electrons to flow through the metal?
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(c)Explain what happens to the atoms in the metal when a piece of copper is pulled into a wire.
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[Higher]
4Nanotechnology promises to revolutionise our world. Nanoparticles and new devices are being rapidly developed but production is still on a very small scale. The properties of nanoparticles that make them useful can cause problems if they are made in large quantities. These include explosions because of spontaneous combustion on contact with air.
(a)What are nanoparticles?
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(b)Suggest two reasons why nanotechnology is being developed rapidly.
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(c)Why are nanoparticles more likely to catch fire when exposed to air compared with normal materials?
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5Piezoceramics are smart materials that can be made to vibrate by passing an electric current through them. They can be made small enough to work inside mobile phones.
(a)Suggest a possible economic advantage of piezoceramics.
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(b)Suggest an environmental advantage of piezoceramics.
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Some smart materials can only be seen at higher temperatures. They can be used in the manufacture of clothing.
(c)Suggest how this feature could be useful.
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6A molecule of pentane can be represented as shown:
(a)What do the letters C and H represent?
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(b)What do the lines between each C and H represent?
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(c)Explain why liquid pentane does not conduct electricity.
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(d)Pentane boils at 36°C. Explain what happens to the molecules of pentane when liquid pentane boils and becomes a gas.
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SECTION C2.3
You should know and / or be able to use / do the following
The relative masses of atoms can be used to calculate how much to react and how
much we can produce, because no atoms are gained or lost in chemical reactions. In
industrial processes, atom economy is important for sustainable development.
To calculate chemical quantities involving formula mass (Mr) andpercentages of elements in compounds
To calculate chemical quantities involving empirical formulae,reacting masses and percentage yield.
To calculate the atom economy for industrial processes and be ableto evaluate sustainable development issues related to thiseconomy.
Atoms can be represented as shown:
Mass number 23
Na
Atomic Number 11
The relative masses of protons, neutrons and electrons are:
Name of particle Mass
Proton 1
Neutron 1
Electron Very small (0)
The total number of protons and neutrons in an atom is called itsmass number.
Atoms of the same element can have different numbers ofneutrons; these atoms are called isotopes of that element.
The relative atomic mass of an element (Ar) compares the mass ofatoms of the element with the 12C isotope. It is an average valuefor the isotopes of the element.
The relative formula mass (Mr) of a compound is the sum of therelative atomic masses of the atoms in the numbers shown in theformula.
The relative formula mass of a substance, in grams, is known asone mole of that substance.
The percentage of an element in a compound can be calculatedfrom the relative mass of the element in the formula and therelative formula mass of the compound.
The masses of reactants and products can be calculated frombalanced symbol equations.
Even though no atoms are gained or lost in a chemical reaction, itis not always possible to obtain the calculated amount of a productbecause:
− the reaction may not go to completion because itis reversible
− some of the product may be lost when it is separated from thereaction mixture
− some of the reactants may react in ways different to theexpected reaction.
The amount of a product obtained is known as the yield. Whencompared with the maximum theoretical amount as a percentage,it is called the percentage yield.
The atom economy (atom utilisation) is a measure of the amountof starting materials that end up as useful products. It is importantfor sustainable development and for economical reasons to usereactions with high atom economy.
In some chemical reactions, the products of the reaction can reactto produce the original reactants. Such reactions are calledreversible reactions.
When a reversible reaction occurs in a closed system, equilibriumis reached when the reactions occur at exactly the same rate ineach direction.
The relative amounts of all the reacting substances at equilibriumdepend on the conditions of the reaction.
Although reversible reactions may not go to completion, they canstill be used efficiently in continuous industrial processes, such asthe Haber process that is used to manufacture ammonia.
The raw materials for the Haber process are nitrogen andhydrogen. Nitrogen is obtained from the air and hydrogen maybe obtained from natural gas or other sources.
The purified gases are passed over a catalyst of iron at a hightemperature (about 450 °C) and a high pressure (about 200atmospheres). Some of the hydrogen and nitrogen reacts to formammonia.
The reaction is reversible so ammonia breaks downagain into nitrogen and hydrogen.
On cooling, the ammonia liquefies and is removed. Theremaining hydrogen and nitrogen is re-cycled.
The reaction conditions are chosen to produce a reasonable yieldof ammonia quickly.
Now try these exam style questions
How much?
1Hydrogen has three isotopes
(a)What are isotopes?
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(b)How many protons, neutrons and electrons are there in an atom of3H?
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(c)Heavy water contains atoms of the isotope hydrogen 2instead of hydrogen 1
What is the mass of one mole of heavy water?
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2Tablets taken by people with iron deficiency anaemia contain 0.200 g of anhydrous iron(II) sulfate, FeSO4.
(a)Calculate the relative formula mass of iron(II) sulfate, FeSO4.
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(b)Calculate the percentage of iron in iron(II) sulfate.
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(c)Calculate the mass of iron in each tablet.
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3The equation for the main reaction to make ammonia is:
N2 + 3H2⇋ 2NH3
(a)What does the symbol ⇋ tell you about this reaction?
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(b)The flow diagram shows the main stages in making ammonia.
(i)Name the two raw materials A and B.
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...... (2)
(ii)What is the purpose of the iron in the reactor?
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(iii)Why do the nitrogen and hydrogen not react completely.
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(iv)How is wastage of unreacted nitrogen and hydrogen prevented?
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4The equation for the reaction of calcium carbonate with hydrochloric acid is:
CaCO3 + 2HCl CaCl2 + CO2 + H2O
(a)How many moles of hydrochloric acid react with one mole of calcium carbonate?
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(b)How many moles of calcium chloride are produced from one mole of calcium carbonate?
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(c)What is the mass of calcium chloride that can be made from one mole of calcium carbonate?
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(d)What is the mass of one mole of calcium carbonate?
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(e)A student reacted 10 g of calcium carbonate with hydrochloric acid and collected 7.4 g of calcium chloride. What was the percentage yield?
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[Higher]
5Chromium can be obtained from chromium oxide, Cr2O3, by reduction with aluminium or carbon. For the first reaction, chromium is mixed with aluminium and ignited in a crucible. The reaction using carbon is done at high temperatures in a low-pressure furnace. The equations for the reactions are:
Cr2O3 + 2Al 2Cr + Al2O3
2Cr2O3 + 3C 4Cr + 3CO2
(a)Calculate the maximum mass of chromium that can be obtained from one mole of chromium oxide.
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(b)Calculate the percentage atom economy for both reactions to show which reaction has the better atom economy.
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(c)Suggest one advantage and one disadvantage of using carbon to manufacture chromium.
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er]
6Ibuprofen is used as a pain killer throughout the world. You might know it as Nurofen or Ibuleve. The traditional way to manufacture ibuprofen involved a lot of chemical reactions and produced a lot of waste. The atom economy was just 32%.
Recently it became possible for any pharmaceutical (drug) company to make ibuprofen. As there was a lot of money to be made, the race was on to find the most economic way to make it. This meant cutting down waste. The new method involves catalysts, some of which can be completely recovered and do not go out as waste. The atom economy is increased to 77%, partly because only the active form of ibuprofen is made. This also means that lower doses are needed and they take a shorter time to kill any pain.
Evaluate the two methods of manufacture in terms of the social, economic and environmental issues involved.
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SECTION C2.4
You should know and / or be able to use / do the following
Being able to speed up or slow down chemical reactions is important in everyday life
and in industry. Changes in temperature, concentration of solutions, surface area of
solids and the presence of catalysts all affect the rates of reactions.
To interpret graphs showing the amount of product formed (orreactant used up) with time, in terms of the rate of the reaction
To explain and evaluate the development, advantages anddisadvantages of using catalysts in industrial processes.
The rate of a chemical reaction can be found by measuring theamount of a reactant used or the amount of product formed overtime: