1.6 electron arrangements and ionisation energy

• electrons can be removed from atoms and the energy it takes to remove them can be measured, this is called ionisation energy
• ionisation energy is the energy required to remove a mole of electrons from a mole of atoms in the gaseous state
• ionisation energies generally increase across a period because the nuclear charge is increasing and this makes it more difficult to remove an electron
• the nearer the nucleus, the higher the ionisation energy of that electron