Periodicity (OCR A Level Chemistry)

X₃Y₆

X₃Y₂

X₂Y₃

X₆Y₃

First ionisation energy

Number of electrons in the outer shell

Number of protons in the nucleus

Relative atomic mass

Silicon

Phosphorus

Sulfur

Chlorine

Melting point decreases from lithium to carbon

Boiling point decreases from fluorine to iodine

First ionisation energy decreases from lithium to caesium

First ionisation energy increases from nitrogen to oxygen

P atoms have less repulsion between p-orbital electrons than S atoms

P atoms have a smaller nuclear charge than S atoms

P atoms lose an electron from the 3s subshell, while S atoms lose an electron from the 3p subshell

P atoms have an odd number of electrons, while S atoms have an even number

ZOH

Z(OH)₂

Z(OH)₃

Z(OH)₄

B

C

N

O

Diamond and graphite both conduct electricity due to delocalised electrons in their structure

The bond angles in the two structures are not the same

Diamond is macromolecular and graphite is simple molecular

All the valence electrons are covalently bonded in both graphite and diamond

Silicon, phosphorus, sulfur

Sodium, magnesium, aluminium

Aluminium, silicon, phosphorus

Magnesium, aluminium, silicon

Na

Mg

K

Al

N atoms have less repulsion between p-orbital electrons than O atoms.

N atoms have a smaller nuclear charge than O atoms.

N atoms lose an electron from the 2s subshell, while O atoms lose an electron from the 2p subshell.

N atoms have an odd number of electrons, while O atoms have an even number.

The first ionisation energy generally increases across a period due to increased nuclear charge and shielding.

First ionisation energy drops between magnesium and aluminium because the outer electron is in the 3p subshell which is higher in energy than the 3s orbital. 

First ionisation energy drops between nitrogen and oxygen because the spin-pair repulsion of the 2p electron means that this electron is higher energy.

First ionisation energy down a group increases due to increased nuclear charge. 

Calcium and phosphorus 

Sodium and oxygen

Magnesium and nitrogen

Phosphorus and potassium