Atomic Structure, Isotopes and Electronic Configurations and Ionisation Energy and Periodic Trends

Relative atomic mass

Weighted mean mass of an element relative to 1/12th the mass of an atom of carbon-12

Relative isotopic mass

the mass of an atom of an isotope compared to 1/12th the mass of an atom of carbon-12

Orbital

A region around the nucleus that can hold up to two electrons with opposite spins

First ionisation Energy

The energy required to remove one electron from one mole of gaseous atoms to form one mole of 1+ gaseous ions

1st I.E. down a group

decreases

atomic radius increases

more shells so increased shielding

outweighs increasing nuclear charge

nuclear attraction on outer electron shells decreases

1st I.E. across a period (general trend)

increases

nuclear charge increases

same shells so similar shielding

nuclear attraction increases

atomic radius decreases

1st fall in ionisation energy across a period (e.g. Be to B)

2p subshell starts filling

2p subshell has higher energy than 2s subshell

2p electron is easier to remove than one of the 2s electrons

1st I.E. is lower

2nd fall in ionisation energy across a period (e.g. N to O)

start of electron pairing in 2p orbitals of 2p subshells

paired electrons repel each other

easier to remove paired electron

1st I.E. is lower