- All things are made of atoms
- A substance made from only 1 atom is called an element
- Atoms of each element are represented by a chemical symbol, for example oxygen is represented by an 'O', or Sodium is represented by 'Na'.
- Atoms have a nucleus in the centre made up of protons and neutrons.
- The protons and neutrons are surrounded by electrons.
- The relative electrical charges are:
Protons: +1 Charge
Neutrons: 0 Charge
Electrons: -1 Charge
- In an atom, the number of protons is equal to the number of electrons, and therefore each atom has a neutral charge (they cancel each other out).
- All atoms of the same element have the same amount of protons.
- The number of protons in an element is called the atomic number.
- The sum of the protons and neutrons equal the element's mass number.
- Electrons occupy different 'shells' - each electron is in a particular shell.
- Electrons occupy the innermost shells.
- The shells can hold a specific amount of electrons:
1st Shell: 2 electrons
2nd Shell: 8 elctrons
3rd Shell: 8 electrons
4th Shell: 18 electrons
(no need for further knowledge for GCSE)
On the next page it is shown how electron shells are drawn for GCSE.
Electron Shell Drawing - Potassium ('K'):
Chemical Reactions 1
- When elements react, they form a compound.
- This reaction involves giving, taking, or sharing electrons to form ions or molecules.
- Ions are compounds that are a mix of metals and non-metals.
- Molecules are compounds that are made of non-metals.
- Molecules are held together by covalent bonds.
- Metals lose electrons to become positive ions.
- Non-metals gain electrons to become negative ions.
- These chemical reactions are represented by equations, such as:
CH4+ 2 O2 CO2+ 2 H2O
- No atoms are lost or created during a chemical reaction
- Limestone is mainly composed of Calcium Carbonate (CaCO3)
- Calcium Carbonate can be decomposed by thermal decomposition (heating)
- The carbonates of zinc, magnesium, copper, sodium and calcium can be decomposed using the same method
- Calcium oxide reacts with water to produce calcium hydroxide - an alkali used to neutralise acids
- Calcium hydroxide then reacts with calcium dioxide to produce Calcium Carbonate
- Limestone is damaged by acid rain
- Limestone can be heated with clay to produce cement
- Cement can be mixed with sand to make mortar, and aggregate and sand to produce concrete.