periodicity

• what happens to atomic radius across period 3?

  Decreases

  nuclear charge increases (more protons)

  this pulls the outer shell of electrons closer towards the nucleus

  shielding remains constant as electrons r in the same shell
• what happens to the melting point across period 3?

  first three elements are metals so they have metallic bonding

  it increases as you go across, the charge on the electron increases which increases the number of delocalised electrons so a stronger bond

  sillicon has the highest as its a giant covalent structure which is macromollecular it has MANY strong covalent bonds so a large amount of energy is needed to overcome it

  phosphorous has vdw only

  sulfur is bigger than phosphorous so has stronger vdw

  AR has the smallest as its an individual atom
• why is fluride bigger than sodium?

  the fluride ion has a fewer number of protons so a weaker nuclear charge so the outer electron is held furhter away from the nucleus
• why is mg2+ smaller than na+?

  it has an increased nuclear charge so its holding the outer electron more closely to the nucleus