Periodicity 8.1-8.4

Electronegativity 

• It decreases down the group because nuclear charge, sheilding and radius all increase 
• It increases across the period because nuclear charge increases, sheilding stays the same and radius decreases

Type of bonding 

• Si has a structure like diamond so is a giant covalent. Melting requires breaking covalent bonds so needs a lot of energy 
• P,S, Cl are simple molecular so the intermolecular forces are van der waals and require less energy to overcome.
• Larger the molecule the more electrons the more van der waals

Trends in melting/ boiling points 

• The mp/bp depends…