Atomic structure and periodicity

General Trend Down Any Group

• The first ionisation energy decreases down the group

because…

• the atomic radius increase ie the outer electron is further from the nucleus

• shielding increases due to the more filled inner energy shells.

• Shielding and distance outweigh the increased nuclear charge.

General Trend Across Period 2 & Period

• the first ionisation energy increases.

because…

• the Nuclear charge increase due to more protons.

• shielding remains constant, since the electrons added are in the same main enlectron shell.

• due to an extra proton, there is an increased exerted force on the energy levels and causes the atomic radius to slightly decreases and there is stronger electrostatic forces of attraction.

Period 3 exception 1; Group2 → group 3 (Mg → Al)

• the first ionisation energy decreases from Mg to Al

because…

• Al’s outer electron is in 3p sub-shell where as Mg’s is in 3s.

• the 3p sub-shell is higher energy and is further from the nucleus and is receiving the extra shielding of 3s.

• so has a greater effect than the slightly higher nuclear charge.

Period 3 exception 2; group 5 → group 6 (p→ s)

• the first ionisation energy decreases from P to S

because…

• P has a configuration of 3p3, which is singly occupied p-orbitals.

• where as S has a configuration of 3p4, which is doubly filled p-orbital.

• spin-pair repulsion between the 2 electrons in the same 3p orbital makes the elctron easier to remove.

Successive ionisation energy trend

• Each successive IE is higher in energy than the last 1st<2nd

• electrons are being removed from an increasingly positive ion, Electrostatic force of attraction

• A sudden jump in IE indicates the elctron is being removed from a shell closer to the nucleus.

definition of 1st Ionisation energy

it is the energy required to remove 1 mol of e- from 1mol of gaseous state atoms to form 1mol of gaseous state 1+ ions

what is mass spectrometry

is an analytical chemistry technique that helps identify the amount ( relative abundance) and type of chemicals in a sample