The first ionisation energy is the energy needed to remove 1 electron from each atom of an element in 1 mole of gaseous atoms, to form 1 mole of gaseous ions with a +1 charge.
Equation for first Ionisation energy
X(g) —> X+(g) + e-
Equation for second Ionisation energy
X(g)^+ -> X(g) ^2+ + e-
Ionisation trends down a group.
Ionisation energy decreases:
Atomic Radius increase and Shielding Increase. Outer e- further away from nucleus. Weaker attractive forces, less energy required to remove e-.
Ionisation Trends across a period.
Ionisation energies increase; increasing number of protons in nucleus so increased nuclear charge, more energy required to remove e-
Deviation in ionisation energies increase Across a period
aluminium: the outer electron in Aluminium sits In the 3p orbital, a slightly higher sub shells from the nucleus compared to the electron in magnesium
Sulfur: phosphorus and sulfur both have outer electrons in 3p orbital: shielding is the same. However removing electron from sulfur Involves taking it from an orbital with 2 electrons in it: electrons repel so less energy required to remove it.
