Chemistry 1.1

Chemistry 1.1

1. Atoms and Elements

   • Atomic Structure
     • The Nucleus is the middle of the atom, it contains protons and neutrons. Protons are positively charged and neutrons are neutral. Overall the nucleus is positively charged. The electrons move around the nucleus and are negatively charged, they occupy the shells around the nucleus. The number of protons are equal to the number of electrons, atoms have no charge overall. If some electrons are added or removed, the atom becomes charged and becomes an ion. Atoms have different numbers of protons, electrons and neutrons but it is the number of protons that decide what atom it is(e.g. 1 proton is hydrogen). If a substance contains only one type of atom it is a element.
   • The Periodic Table
     • Atoms can be represented by a one or two lettered symbol, e.g. C=Carbon, O=Oxygen, Na=Sodium, Fe=Iron.
     • The periodic table is laid out so all elements with similar properties form columns. The vertical columns are called groups and all of the elements in a group have the same number of electrons in their outer shell. This is why elements in the same group have similar properties, if you know the properties of one element you can predict properties of other elements. E.g. Group 1 are all metals and they react in the same way. Group 0 are noble gases and all have eight electrons in their outer shell (apart from helium) so they're stable and unreactive.
   • Electron shells
     • Electrons always occupy shells. The lowest energy levels are always filled first (the ones closest to the nucleus). Only a certain number of electrons are allowed in each shell: 1st shell: 2, 2nd shell: 8, 3rd shell:8. Atoms are much happier when they have full electron shells and in most atoms they don't have a full outer shell so it makes them want to react to get a full shell.
   • Compounds
     • A compound is a substance that is made from 2 or more elements which are chemically bonded.It is usually difficult to separate the 2 elements out again. Making compounds involves atoms giving away, taking or sharing electrons. The properties of a compound are totally different from the properties of the original elements. Compounds can be small molecules like water or large lattices like sodium chloride.
       • Covalent bonding is only in non-metals so consists of molecules. Covalent bonding the the sharing of electrons until the outer shell is full. One pair of electrons being shared=Single bond. Two pairs=Double bond. Three pairs=Triple bond.
       • A compound that is formed from a metal and a non-metal consists of ions. The metal atoms lose electrons to form positive ions and the non-metals gain electrons to form negative ions.
   • Balancing Equations
     • Atoms aren't lost or made in chemical reactions. During chemical reactions things don't appear or disappear. You always have the same amount of atoms at the end of the reaction as you did at the start. Because atoms aren't gained or lost the mass of the reactants equals the mass of the products. E.g. If you completely react 6g of magnesium with 4g of oxygen you end up with 10g of magnesium oxide.
       • 1) Find an element that doesn't balance and pencil in a number to try and sort it out. 2) See where it gets you. It may create another imbalance so pencil in another number and see where that gets you. 3) Carry on chasing unbalanced elements to sort the equation out.

2. Limestone

   • The scientific name for limestone is Calcium Carbonate (CaCO3). When Limestone is thermally decomposed (heating a compound and it breaks down) you make Calcium Oxide (CaO) and Carbon Dioxide (CO2). Magnesium, copper, zinc and sodium chlorides also thermally decompose in this way (mainly at high temperatures). Calcium carbonate also reacts with acid to make a calcium salt, carbon dioxide and water: Calcium Carbonate (CaCO3) + Sulfuric Acid (H2SO4) = Calcium Sulfate (CaSO4) + Carbon Dioxide (CO2) + Water (H2O). The type of salt produced depends on the type of acid.
     • When you add water to calcium oxide you get calcium hydroxide. Calcium oxide (CaO) + Water (H2O) = Calcium Hydroxide Ca(OH)2. Calcium hydroxide is an alkali which can be used to neutralise acidic soil. Powdered limestone can be used for this too but calcium hydroxide works much faster. Calcium hydroxide can also test for carbon dioxide. If you make a solution of calcium hydroxide in water (limewater) and bubble gas through it the gas will turn cloudy if there is carbon dioxide present.
       • Cement= powdered limestone + powdered clay (heated). Concrete= Cement + sand + aggregate (crushed rock/water+gravel). Mortar (what you stick bricks together with = Sand + Water.
   • Limestone quarrying
     • Disadvantages: Limestone quarries make large holes in the ground when the rock explodes, the explosions make loud noises and create a lot of dust, they destroy many habitats, when the limestone has to be transported away it creates more noise and pollution, waste materials produce unsightly tips, it is a large eye-sore. Cement factories also create a lot of dust so can cause breathing problems. Energy is needed to produce cement and quicklime, the energy is mainly from burning fossil fuels which creates pollution.
     • Advantages: limestone is used for building houses and roads and chemicals are used in making dyes, paints and medicines. Limestone products are used to neutralise acidic soil and can neutralise acidic water in lakes and rivers. Limestone can also be used in power stations to neutralise sulfur dioxide (causes acidic rain). The quarry can also provide jobs for local people and can boost the local economy, Landscaping and restoration usually occurs when quarrying is complete.

3. Extracting Metals

   • Ores are rocks that contain enough metal to make it financially worth extracting the metal from it. In many cases the ore is an oxide of the metal e.g. the main aluminium ore is called bauxite (aluminium oxide). Most metals need to be extracted from their ores using a chemical reaction. The economics of metal extraction can change over time e.g. if the market price of the metal drops it might not be financially worthwhile extracting it but if it increases it may be financially worthwhile extracting more. A metal can be extracted from its ore chemically-by reduction or by electrolysis. Some ores may have to be concentrated before to metal is extracted (getting rid of the extra rocky material). Electrolysis can also be used to purify the metal.
     • Reduction: A metal can be extracted from its ore chemically by reduction using carbon. When an ore is reduced oxygen is removed from it e.g. iron oxide + carbon = iron + carbon dioxide. The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon. This can only happen if the metal is below carbon in the reactivity series and if it is higher it has to be extracted by electrolysis which is more expensive.
     • Electrolysis: Metals that are more reactive than carbon have to be extracted by electrolysis of molten compounds. This is much more expensive due to the lrge amounts of energy used. E.g. A high temperature is needed to melt aluminium oxide so that aluminium can be extracted- this requires a lot of energy, which makes it more expensive. Electrolysis is the breaking don of a substance using electricity. It requires a liquid to conduct electricity, called electrolyte. Electrolytes are often metal salt solutions made from the ore or molten metal oxides. The electrolytes has free ions-these conduct electricity and allow the whole thing to work. Electrons are taken away by the (positive) anode and given away by the (negative) cathode. As ions gain or lose electrons they become atoms or molecules and are released.
       • How electrolysis is used to get copper:

4. Metals

5. Crude Oil

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