The number of protons in an atom.
The number of protons plus the number of neutrons in an atom.
A substance made up of one type of atom.
Atoms with the same number of protons but different numbers of neutrons.
Relative Isotopic Mass
The mass of an atom of an isotope compared with carbon-12, which has a mass of 12.
Relative Atomic Mass (Ar)
The average mass of an atom of an element compared with carbon-12, which has a mass of 12.
1st Ionisation Energy
The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.
Successive Ionisation Energy
The energy required to remove 1 mole of electrons from 1 mole of positive ions in the gaseous state.
The Pattern of Ionisation Energy
- As electrons are removed, the number of protons remains the same.
- The remaining electrons are therefore more strongly attracted to the nucleus.
- More energy is needed as successive electrons are removed.
The number of atoms in 12g of carbon-12 (6.02 x 10^23)
[^ means 'to the power of']
The mass of one mole of a substance.
Columns of the periodic table, which contain atoms with similar chemical and physical properties.
Rows of the periodic table, which show repeating trends in chemical and physical properties.
The repeating pattern of reactivity across different periods.
1st Ionisation Energy in Groups
- As you move down a group, the outer electrons are in energy levels further away from the nucleus.
- There is also a greater sheilding effect, so the forces between the nucleus and the electrons are weaker.
- Therefore, the ionisation energy required to remove the electrons will decrease.
1st Ionisation Energy in Periods
- As you move across a period, electrons are added to the same shell.
- The number of protons in the atom increases.
- Therefore, the electrons are more strongly attracted to the nucleus.
- As such, the ionisation energy needed to remove the electrons increases.
An attraction between oppositely charged ions.
The sharing of a pair of electrons between atoms.