ionisation energy

what is ionisation energy?

The energy required to remove one mole of electrons from one mole of gaseous atoms

ionisation energy down a group

decreases

why does ionisation energy decrease down a group

number of protons increases (so nuclear charge increases), radius of atom increases, more shells so shielding increases

ionisation energy across a period

increases

why does ionisation energy increase across a period

number of protons increases so nuclear charge increases, creating a stronger attraction between nucleus and electrons, pulling them closer and reducing atomic radius, constant shielding

large increases of ionisation energy

shows removal of electron from a shell closer to nucleus

What is electronegativity?

ability of an atom to attract electrons towards itself in a covalent bond

electronegativity across a period

increases as atomic radius decreases and nuclear charge increases whilst shielding is constant

Trend in ionisation energy across groups 2 and 3

• Ionisation energy decreases from group 2 to group 3.
• Group 2 elements have outer electrons in the 2s orbital.
• Group 3 elements have outermost electrons in the higher energy 2p orbital.
• The 2p electrons are further from the nucleus and experience more electron shielding.
• This makes it easier to remove 2p electrons compared to 2s electrons.

ionisation energy across group 5 and 6

dips

Group 6 elements outermost electron paired in a p-orbital, so has increased electron repulsion, so easier to remove

why does the successive ionisation energy of an element increase

Removing the outer electron from an atom forms a positive ion

Removing an electron from a positive ion is more difficult than from a neutral atom

As more electrons are removed, the attractive forces increase due to decreasing shielding and an increase in the proton to electron ratio

Negatively charged electrons have a stronger force of attraction to the positive ion

Why does sodium have a much lower first ionisation energy than neon?

Na has its outer electrons in a 3s sub shell further from the nucleus and is more shielded

So easier to remove, need lower IE

Why is there a small drop from Mg to Al?

aluminiums outer electrons removed from higher energy 3p orbital, whereas magnesium’s is removed from the lower energy 3s orbital

Easier to remove from 3p as they are higher in energy and slightly shielded

Why is there a small drop from Phosphorous to Sulphur?

S has 4 electrons in 3p sub shell- fourth is paired with another in the 3p sub shells

Causes slight repulsion, so less IE needed