periodic table

• describe the trend in atomic radius across a period

  decreases across a period

  shielding remains almost constant

  outer electrons feel greater attraction to the positively charged nucleus
• describe the trend in atomic radius down a group

  increases down a group

  although nuclear charge increases

  this is more than offset by an increase in the number of shells of electrons

  and increased shielding
• describe the trend in first ionisation energy down a group

  decreases down a group

  although nuclear charge increases

  this is more than offset by increased shielding

  and increased atomic radius

  therefore the outer electron is further from the attraction of the nucleus
• describe the trend in first ionisation energy across a period

  increases across a period

  as nuclear charge increases

  shielding remains almost constant

  and atomic radius decreases

  therefore the outer electron is further from the attraction of the nucleus

  EXCEPTIONS

  decreases for B (period 2) and Al (period 3)

  the electron is being removed from a half full p - subshell

  whish is half full with extra stability

  and further from the attraction of the nucleus

  therefore requires less energy to remove

  as opposed to a filled s - subshell with associated stability for Be / Mg
• describe the trend in electronegativity across a period

  increases across a period (to group 7)

  as nuclear charge increases

  and atomic radius decreases

  the bonding pair of electrons are more attracted to the nucleus

  within a covalent bond
• The trend in melting point (mpt) and boiling point (bpt) from Na to Al:

  • Increases from Na to Al
  • The strength of the metallic bond increases
  • This depends on the strength of electrostatic attractions between the sea of delocalised electrons and the lattice of cations
• Al has 3 delocalised electrons per atom and a lattice of Al3+ cations, making it the strongest metallic bond that requires the most energy to break, hence having the highest mpt / bpt
• Mg has 2 delocalised electrons per atom and a lattice of Mg2+ cations, making it the next strongest metallic bond with the next highest mpt / bpt
• Na has 1 delocalised electron per atom and a lattice of Na+ cations, making it the weakest metallic bond that requires the least energy to break, hence having the lowest mpt / bpt
• describe the mpt / bpt in Si

  higher than Na

  giant covalent structure with many strong covalent bonds between molecules

  in a 3D structure

  that requires a lot of energy to break
• decribe the mpt / bpt in P4, S8 and Cl2

  lower than Si

  simple molecular covalent molecules with only weak vdW between molecules

  S8 has the most e-, therefore the strongest vdW between molecules

  which require the most energy to break

  therefore has the highest mpt / bpt

  followed by P4

  followed by Cl2
• describe the mpt / bpt in Ar

  lower than Cl2

  monoatomic with only weak vdW between atoms

  that require very little energy to break

  therefore has a very low mpt / bpt