Reactivity and Using Metals

• Some metals are more reactive than others
• Some metals tarnish because they react with oxygen in the air
• The tarnishing of iron is called rusting
• Rusting occurs when iron reacts with oxygen in the presence of water
• The reactivity series is a list of metals in order from most reactive at the top to least reactive at the bottom
• When a metal reacts with an acid, a salt and hydrogen gas are made
• Bubbles observed in the solution indicate that a gas is being made in the reaction
• By observing the reactions of metals and acids, it is possible to deduce the order of reactivity of the metals
• The reactivity series can be used to make predictions about the reactions of metals, such as whether a reaction will take place and how vigorous that reaction will be
• Most metals are found in naturally occurring compounds and  have to be extracted from them
• Ores are rocks or minerals which contain enough metal that can be extracted economically
• Carbon and hydrogen can be used to extract metals from their ores by displacement reactions
• Carbon or hydrogen will displace a less reactive metals from their ores

Potable Water

• Urban lifestyles and industrial processes produce large amounts of wastewater that require treatment before being released into the environment. 
• Sewage and agricultural wastewater require removal of organic matter and harmful microbes. 
• Industrial wastewater may require removal of organic matter and harmful chemicals.
• Sewage treatment includes screening and grit removal, sedimentation to produce sewage sludge and effluent, anaerobic digestion of sewage sludge and aerobic biological treatment of effluent.
• Water of appropriate quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. 
• Water that is safe to drink is called potable water. 
• Potable water is not pure water in the chemical sense because it contains dissolved substances.
• The methods used to produce potable water depend on available supplies of water and local conditions.
• In the United Kingdom (UK), rain provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers
• Most potable water is produced by choosing an appropriate source of fresh water, passing the water through filter beds and sterilising.
• Sterilising agents used for potable water include chlorine, ozone or ultraviolet light.
• Fluoride is added to drinking water in some countries to prevent tooth decay
• Some people may not support this for reasons such as they have not consented to it, or they feel that there is insufficient scientific evidence to support the benefits of this.
• If supplies of fresh water are limited, desalination of salty water or sea water may be required. 
• Desalination can be done by distillation or by processes that uses membranes such as reverse osmosis. 
• These processes require large amounts of energy.

Using Earth’s Resources

• Humans use the Earth’s resources to provide warmth, shelter, food and transport.
• Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels.
• Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials.
• Sustainable development is development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.
• Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone. Borosilicate glass, made from sand and boron trioxide, melts at higher temperatures than soda-lime glass.
• Clay ceramics, including pottery and bricks, are made by shaping wet clay and then heating in a furnace.
• The reduction in use, reuse and recycling of materials by end users reduces the use of limited resources, use of energy sources, waste and environmental impacts.
• Metals, glass, building materials, clay ceramics and most plastics are produced from limited raw materials. Much of the energy for the processes comes from limited resources.
• Some products, such as glass bottles, can be reused. Glass bottles can be crushed and melted to make different glass products.
• Other products cannot be reused and so are recycled for a different use.

Life Cycle Assessments (LCAs)

• Life cycle assessments (LCAs) are carried out to assess the environmental impact of products in each of these stages: extracting and processing raw materials, manufacturing and packaging, use and operation during its lifetime, disposal at the end of its useful life, including transport and distribution at each stage
• Use of water, resources, energy sources and production of some wastes can be quantified. Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process
• Selective or abbreviated LCAs can be devised to evaluate a product but these can be misused to reach pre-determined conclusions, e.g. in support of claims for advertising purposes
• An evaluation should take into account advantages, disadvantages and a justified conclusion

Sources of Information

• Sources of information online can be reliable and unreliable
• Reliable sources of information are written by experts, are peer-reviewed by other experts, are current or updated regularly and have a clear intent or purpose
• Citing sources of information within a report allows the reader to check that the information comes from a reliable source and that the facts presented can be backed up elsewhere

Disciplinary Knowledge

• Cite sources of information
• Interpret the reliability of sources of information
• Apply the idea that whenever a measurement is made, there is always some uncertainty about the result obtained.
• Use the range of a set of measurements about the mean as a measure of uncertainty.
• Understand the terms mean, mode and median

Practical Skills

• Safe use of equipment to separate mixtures using distillation
• Use software to carry out research and report findings
• Report findings with appropriate tone, format and content for a particular audience
• Use technology such as MS Excel and data loggers to generate a graph of results digitally.

Atoms, Elements and Compounds

• All substances are made of atoms. An atom is the smallest part of an element that can exist
• Atoms of each element are represented by a chemical symbol, e.g. O represents an atom of oxygen, Na represents an atom of sodium
• There are about 100 different elements. Elements are shown in the periodic table
• Compounds are formed from elements by chemical reactions
• Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change
• Compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed
• Compounds can only be separated into elements by chemical reactions
• Chemical reactions can be represented by word equations or equations using symbols and formulae

Atomic Structure

• Atoms are very small, having a radius of about 1x10^-10 metres
• The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons
• The radius of a nucleus is less than 1/10 000 of the radius of an atom
• Most of the mass of an atom is concentrated in the nucleus
• In the periodic table, each element appears with two numbers: the atomic number and the mass number
• The atomic number of an element is equal to the number of protons in the nucleus of an atom of that element
• In a neutral atom (an atom with no overall charge), the number of protons (+) is equal to the number electrons (-)
• Different elements have different atomic numbers, and therefore different numbers of protons in the nucleus of their atom
• The mass number of an element is equal to the number of neutrons + protons in the nucleus of an atom of that element
• To determine the number of neutrons in the nucleus of an atom of an element, the atomic number should be subtracted from the mass number

Electronic Configuration

• The electrons are arranged at different distances from the nucleus (in different energy levels, or shells)
• The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level)
• The electrons in an atom occupy the lowest available energy levels first (which are the innermost available shells)
• Electrons will fill the lowest available energy level before moving to a higher energy level
• The electron shell (or energy level) closest to the nucleus can take two electrons
• The second energy level takes up to eight electrons
• If the outermost energy level is full, the atom will be stable (unreactive)
• The electronic structure of an atom can be represented by numbers or by a Bohr diagram. For example, the electronic structure of sodium is 2,8,1 or showing two electrons in the lowest energy level, eight in the second energy level and one in the third energy level

Isotopes

• Atoms of the same element can have different numbers of neutrons. These atoms are called isotopes of that element
• Isotopes are atoms of the same element with different mass numbers due to different numbers of neutrons in the nucleus
• Isotopes of an element will all have the same atomic number, because the number of protons is always the same for all atoms of that element
• Isotopes of an element will have different mass numbers because they have different numbers of neutrons
• Isotopes of an element can be represented as ‘[element name]-[mass number]’, for e.g., carbon-12 and carbon-14
• The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element
• The relative atomic mass does not have a unit

The Atomic Model

• New experimental evidence may lead to a scientific model being changed or replaced
• Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
• JJ Thompson discovered the electron
• JJ Thompson developed the plum pudding model of the atom. This model suggested that the atom is a ball of positive charge with negative electrons embedded in it
• Geiger, Marsden and Rutherford carried out a famous experiment called the Gold Foil (or alpha scattering) experiment. The results from this experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• The nuclear model of the atom replaced the plum pudding model and is the model we use to this day
• Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observation
• James Chadwick discovered the neutron
• Our knowledge of atoms is still developing today

The Periodic Table

• The elements in the periodic table are arranged in order of atomic number and so that elements with similar properties are in columns, known as groups
• The table is called a periodic table because similar properties occur at regular intervals (periodically)
• Elements in the same group in the periodic table have the same number of electrons in their outer shell (outer electrons) and this gives them similar chemical properties
• The early periodic tables were incomplete, and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
• Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and, in some places, changed the order based on atomic weights
• The elements in Group 0 of the periodic table are called the noble gases
• They are unreactive and do not easily form molecules because their atoms have stable arrangements of electrons
• A stable electronic configuration is one in which the outer shell of electrons is full
• The noble gases have eight electrons in their outer shell, except for helium, which has only two electrons
• The boiling points of the noble gases increase with increasing relative atomic mass (going down the group)
• The elements in Group 1 of the periodic table are known as the alkali metals
• The Alkali metals have one electron in their outer shell
• Alkali metals are soft, shiny metals with low melting and boiling points
• In Group 1, the reactivity of the elements increases going down the group
• Alkali metals react vigorously with water to form the metal hydroxide and hydrogen gas
• The equations for the alkali metals’ reactions with water take the form ‘lithium + water → lithium hydroxide + hydrogen’ which can also be written as ‘2Li + 2H2O → 2LiOH + H2’.
• The metal oxides produced by the reactions of alkali metals with water are alkaline
• When added to water, the alkali metals will move rapidly across the surface of the water. This is caused by the production of hydrogen gas.
• When reacting with water, the alkali metals will form a spherical shape. This is caused by the heat of the reaction.
• When alkali metals react with water, sometimes the heat of the reaction will cause the hydrogen gas produced to be set alight. This causes an orange flame to be seen (in the case of sodium) or a lilac flame to be seen (in the case of potassium).
• The alkali metals react with oxygen to form metal oxides
• The alkali metals are stored under oil to prevent reaction with oxygen, also known as corrosion.
• Corrosion makes the alkali metals less shiny.
• The equations for the alkali metals reactions with oxygen take the form ‘lithium + oxygen → lithium oxide’ which can also be written as ‘4Li + O2 → 2Li2O’
• The elements in Group 7 of the periodic table are known as the halogens
• The halogens all have similar reactions because they all have seven electrons in their outer shell.
• The halogens are non-metals and consist of diatomic molecules
• Diatomic molecules consist of pairs of atoms bonded together
• Chlorine is a pale green gas at room temperature
• Bromine is a brown/orange liquid at room temperature
• Iodine is a black or purple solid at room temperature
• In Group 7, the further down the group an element is the higher its relative molecular mass, melting point and boiling point
• The melting and boiling points of the halogens increase going down the group because the molecules become larger, the forces between the molecules become stronger, and so more energy is needed to overcome these forces.
• In Group 7, the reactivity of the elements decreases going down the group. This is because the atomic radius increases moving down the group. The further the outer shell is  from the nucleus, the harder it will be to attract the electron required for a stable electronic configuration.
• The halogens react with metals to produce metal halides, for e.g., sodium + chlorine → sodium chloride
• The halogens react with hydrogen to produce hydrogen halides, for e.g., hydrogen + chlorine →  hydrogen chloride
• A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
• The transition elements are metals including Cr, Mn, Fe, Co, Ni, Cu with similar properties which are different from those of the elements in Group 1
• Many transition elements have ions with different charges form coloured compounds and are useful as catalysts

Disciplinary Knowledge

• Recognise and use expressions in standard form
• Use prefixes and powers of ten for orders of magnitude (e.g. tera, giga, mega, kilo, centi, milli, micro and nano)
• Make order of magnitude calculations
• Recognise that scientific methods and theories change over time
• Critique and evaluate models, including:
• Make predictions or calculate quantities based on the model or show its limitations
• Give examples of ways in which a model can be tested by observation or experiment
• Evaluate the strengths and limitations of a model
• Interpret a line (scatter) graph
• Understand and use the symbols: =, <>, >, ∝, ~

Practical Skills

• Measure pH

Chemical Reactions and Equations

• Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change
• Compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed
• Compounds can only be separated into elements by chemical reactions
• In chemical equations, the three states of matter are shown as state symbols (s), (l) and (g), with (aq) for aqueous solutions.
• Aqueous means dissolved in water
• The law of conservation of mass states that no atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants
• This means that chemical reactions can be represented by symbol equations which are balanced in terms of the numbers of atoms of each element involved on both sides of the equation
• Mass is always conserved in chemical reactions
• In a chemical reaction where a gas is produced, it may appear that the mass decreases throughout the reaction. In fact, this decreased mass will be due to the gas dissipating into the atmosphere. If the reaction is carried out in a closed container, this will not occur

Relative Atomic and Formula Mass

• The relative atomic mass of an element can be found as the mass number of an element on the periodic table
• Relative atomic mass has the symbol Ar
• The relative formula mass of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula
• Relative formula mass has the symbol Mr
• In a balanced chemical equation, the sum of the relative formula masses of the reactants in the quantities shown equals the sum of the relative formula masses of the products in the quantities shown

The Mole

• Chemical amounts are measured in moles
• The symbol for the unit mole is mol
• The mass of one mole of a substance in grams is numerically equal to its relative formula mass
• One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance
• The number of atoms, molecules or ions in a mole of a given substance is the Avogadro constant. The value of the Avogadro constant is 6.02 x 10²³ per mole
• The measurement of amounts in moles can apply to atoms, molecules, ions, electrons, formulae and equations, for example that in one mole of carbon (C) the number of atoms is the same as the number of molecules in one mole of carbon dioxide (CO2)
• Number of moles can be calculated by dividing mass (g) by relative atomic or formula mass

Concentration

• Many chemical reactions take place in solutions
• The concentration of a solution tells you how much solute is dissolved in a given volume of solution
• Concentration can be defined as the mass of substance per unit volume or as the number of moles of substance per unit volume
• Volume means the amount of space that a substance takes up, and can be measured in cm³, dm³, m³, L or mL.
• 1 dm3 is equal to 1 L and equal to 1000 cm³
• To convert from dm³ to cm³ the number should be multiplied by 1000
• To convert from cm³ to dm³ the number should be divided by 1000
• The concentration of a solution can be measured in mass per given volume of solution, e.g., grams per dm3 (g/dm³ or g dm^-3)
• The concentration of a solution can be measured in mol/dm³(mol dm^-3)
• The amount in moles of solute or the mass in grams of solute in a given volume of solution can be calculated from its concentration in mol/dm³

Making Soluble Salts

• Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates
• To produce a soluble salt, an insoluble salt is reacted with acid until no more reacts and the excess solid is filtered off to produce a solution of the salt. The solution is the crystallised to produce solid salt.
• Copper oxide reacts with sulphuric acid solution to produce copper sulphate and water
• This reaction can be represented with the equation CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
• Copper sulphate solution is a blue liquid
• Copper sulphate crystals are blue

Disciplinary Knowledge

• Apply the idea that whenever a measurement is made, there is always some uncertainty about the result obtained.
• Use the range of a set of measurements about the mean as a measure of uncertainty.
• Interconvert units.
• Change the subject of an equation
• Describe a practical procedure for a specified purpose.
• Include a coherent and sensible order of steps, with sufficient detail to obtain valid results, including suggested equipment.

Skills practised

• Safe use of equipment to separate mixtures using evaporation
• Safe use of equipment to separate mixtures using filtration
• Safe use of equipment to separate mixtures using crystallisation
• Measure volumes of liquids accurately
• Measure mass accurately
• Preparation of a pure dry sample of a soluble salt