Do Now: Write the electron configurations of the following atoms and ions Na Mg2+ Al3+ Ne

Kaupapa / Learning Outcome At the end of todays lesson I will know the periodic trend of ionisation energies and understand the reasons for the trend.

Ionisation Energy The energy required to remove an electron from 1 mole of gaseous atoms or ions. The first ionisation energy of neon: Ne (g)  Ne (g) + e- (∆Hi = 2087 kJ mol-1)

Endothermic The energy is require to overcome electrostatic attraction between the nucleus (+) and the valence electrons (-).

Graph of ionisation energies

Trends in Ionisation Energy Two basic trends you need to be aware of Down a group the IE decreases: electrons are further from the nucleus by an extra set of electrons – shielding effect – decrease in electrostatic attraction Across a period the IE increases: More protons in the nucleus = stronger electrostatic attraction

Evidence of subshells What is happening at the following points?

Reasons From Be to B there is a small decrease in IE This is due to the e now being in a p subshell Further from the nucleus than the s subshell From N to O there is a slight decrease in IE N has 3 unpaired e- in a the p subshell = stable whereas O has 1 pair and 2 unpaired = slightly unstable

Successive IE’s 1st IE: M(g)  M+(g) + e- ∆Hi1 = +??? kJ mol-1 2nd IE: M+(g)  M2+(g) + e- ∆Hi2 = +??? kJ mol-1 This can continue until there are no more e- to remove from the element Each time the IE value gets greater, this provides evidence of subshells and e- configuration

2nd Ionisation Energy E.g. for calcium:- Ca (g)  Ca+ (g) + e- ∆Hi = 590 kJ mol-1 Ca+ (g)  Ca2+ (g) + e- ∆Hi2 = 1150 kJ mol-1 The second ionisation energy is much larger than the first.

Why? The ionisation energies increase. As each electron is removed from an atom, the remaining ion becomes more positively charged. Removing the next electron away from an increasing positive charge is more difficult and the ionisation energy is even larger.

Graph of logarithm (log 10) of ionisation energy of sodium against the number of electrons removed.

Why? Why are there large increases between the first and second ionisation energies and again between the ninth and tenth ionisation energies? How does this graph confirm the suggested simple electron configuration of sodium of (2, 8, 1)