What is Ionisation Energy and the three factors that affect it? 2)State and explain the general trend in first ionisation energies for the Period 3 elements.

Ionisation energy is the energy required to remove 1 mole of electrons from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous ions.For example,O_(g)→ O⁺_(g)+ e^-The three factors that affect ionisation energy are the size of the positive nuclear charge, the size of the atom i.e. distance of outermost electron from the nucleus and screening (shielding) effect of inner shell electrons.2) The period 3 elements (Aluminium to Argon) show a general trend in the increase of first ionisation energy. This is because all the electrons that are being removed are in the same level and are being shielded by the 1s²2s²2p6 electrons. The major difference is the increasing number of protons in the nucleus as you move from Aluminium to Argon. This causes greater attraction between the nucleus and the outermost electron, thus increasing the ionisation energy. The increasing nuclear charge also pulls the outermost electrons closer to the nucleus, causing an even greater attraction.