C2 Summaries
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- Created on: 16-12-16 18:22
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- C2 Summaries
- Structure and bonding
- Chemical bonding involves either transferring or sharing electrons in the outer shells of atoms.
- Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions.
- An ionic compound is held together by strong electro-static forces of attraction.
- When atoms share pairs of electrons, they form covalent.
- Structure, properties and uses
- When melted or dissolved in water, ionic compounds conduct electricity. Covalent compounds do not.
- Nanoscience refers to structures that are 1-100mm in size and of the order of a few hundred atoms.
- Metals consist of giant structures of atoms arranged in a regular pattern.
- The properties of thermo-softening and thermosetting polymers depend on what they are made from and how they are made.
- An iIonic compound has a regular structure (giant ionic lattices), high melting and boiling points.
- Diamond and graphite have different properties determined by their different structures.
- Atomic structure, analysis and quantitive chemistry
- The amount of a product obtained is known as the yield.
- The masses of reactants and products can be calculated from balanced symbol equations.
- A reversible reaction is one where the products of the reaction can react to produce the original reactants.
- Elements and compounds can be identified using instrumental methods.
- Atoms of the same element can have different numbers of neutrons.
- The relative mass (A) and the relative formula mass (M) allow numbers of particles to be compared.
- Rates of reaction
- Catalysts change the rate of chemical reactions but are not used up during the reaction.
- The minimum amount of energy that particles must have to react is called the activation energy.
- Chemical reactions can only occur when reacting particles collide. Collision theory explains why changes to conditions affect rates.
- Equation:
- Acids, bases and salts
- Soluble salts can be made from acids by reacting them with metals, insoluble bases, or alkalis. Salt solutions can be crystallised to produced solid salt. Insoluble salts can be made by mixing solutions of ions so that a precipitate is formed.
- Metal oxides and hydroxides are bases. Soluble hydroxides are called alkalis. Ammonia makes an alkaline solution to produce ammonium salts.
- In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water.
- Hydrogen ions, H (aq), make solutions acidic and hydroxide ions, OH (aq), make solutions alkaline.
- Electrolysis
- During electrolysis, positively charged ions move to the negative electrode and are reduced, and negatively charged ions move to the positive electrode and are oxidised.
- Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite.
- When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution.
- Reactions at electrodes can be represented by half-equations, for example:
- Exothermic and endothermic reactions
- An exothermic reaction transfers energy to the surroundings. An endothermic reaction takes in energy from the surroundings.
- If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.
- Structure and bonding
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