Chemistry GCSE Revision

Chemicals of the Natural Environment. Part 1.

Atoms in molecules are held together by strong covalent bonds.
The attractive forces between molecules are weak, so small molecules are often gases.
Molecular compounds do not conduct electricity because their molecules are not charged.
Living things are mainly made up of molecular compounds containing carbon, hydrogen, oxygen and nitrogen, with small amounts of other elements.
Compounds made up of metals and non-metals have giant ionic structures.
Ionic compounds have high melting points because of the strong attraction between the ions.
Ionic compounds conduct electricity when they're molten or aqueous as the ions are free to move.
Salts are ionic compounds.
Silicon dioxide and diamond have giant covaelent structures with atoms held together in a regular network with strong bonds.
Chemicals with giant covalent structures have high melting points and don't dissolve in water.
Giant structures don't conduct electricity as there are no free electrons or ions.
Much of the lithosphere is made up of giant covalent structures based on silicon, oxygen and other elements.
All metal structures have a giant structure of metal atoms.
The metallic bonding between the atoms is strong.

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Electrolysis turns ions back into atoms.
At the anode, positive metal ions gain electrons and become metal atoms.
At the cathode, negative ions lose electrons and turn back into non-metal atoms.
Metals conduct electricity when solid and when molten because the bonding electrons can move.
The oxidising agent helps oxidise something else (becomes reduced).
The reducing agent gains oxygen, taking it away from something else (becomes oxidised).
Actual yield: the mass of the required chemical obtained after separtaing and purifying the product of the chemical reaction.

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Atoms have a central nucleus surrounded by negative electrons.
Chemistry of an element is largely determined by the no. and arranegment of it's electrons.
No. of electrons is equal to the proton no. of the atom.
Elements in the periodic table are arranged in order of their proton no.
Elements in a group have similar characteristics because they have the same no. of electrons in the outer shell.
When metals react with non-metals, the metal atoms lose electrons while the non-metal atoms gain electrons. This produces ionic compounds.
The properties of an ionic compound behave differently from the atoms of molecules in the elements.

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Chemical synthesis provides useful products such as food additives, fertilizers, dyestuffs, paints, pigments and pharmaceuticals.
Acids react in characteristic ways with metals, metal oxides and metal carbonates.
Alkalis neutralise acids to form salts.
All acids have similar properties because they produce hydrogen ions in water.
During a neutralisation reaction, hydrogen ions from an acid reacted with hydroxide ions from an alkali to make water.
Chemists follow the rate of change by measuring the disappearance of a reactant or the info of a product.
Factors which affect rate of change: particle size of solid reactants, the temperature and the presence of a catalyst.
The collision theory: reactions occur as molecules collide.
For the collisions to cause a reaction they must have enough activation energy.
Titration is the method used to test a substances purity.

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Alkali: a compound that dissolves in water to give a solution with a pH higher than 7.
Neutralisation: an alkali can be neutralised by an alkali to form a salt.
Biosphere: all life on earth
Lithosphere: the earth's crust
Atmosphere: gases
Hydrosphere: water
Catalyst: speed up reactions
Combustion: when a chemical rapidly reacts with oxygen, releasing energy
Covalent Bonding: strong attractive forces that hold atoms together in molecules, they form between non-metallic elements
Electrostatic attraction: the force of attraction between between objects with opposite charges
Electron configuration: the number + arrangement of electrons.
Energy level: electrons in an atom have different energy levels and are arranged to show this.
Halogens: the group 7 elements.
Ionic bonding: the force holding together ions in an ionic compounds.

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Metallic bonding: strong attractive forces that hold metal atoms together in a solid metal. They lose their outer electrons to form ions (+). Electrons drift freely around the lattice of positive metal ions and hold the ions together.
Percentage yield: actual yield/theoretical yield

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