Trends in the Periodic Table

• solids have great densities
• gases have small densities
• general decrease across a period
• general increase down the group

• general increase in melting and boiling points down a group
• general decrease in melting and boiling points across a period

• half the distance between nuclei and bonded atoms
• general increase down a group because:
  • there is an increase in the number of electron shells
  • the outer electrons are further from the nucleus
• general decrease across a period:
  • there is an increase in nuclear charge
  • therefore there is an increase in attraction between the nucleus and its outer electrons
  • electrons are held more tightly

First Ionisation Energy

• the energy required to remove one electron from an atom of a certain element
• general increases down a group because:
  • there is an increase in nuclear charge
  • there is a decrease in covalent radii so the electrons are held more tightly
• general decreases across a period because:
  • there is an increase in electron shells causing a shielding effect
  • electrons held less tightly to nuclei

Second Ionisation Energy

• the energy required to remove a second electron from a now singularly positive ion of a certain element
• group 1 elements have a much higher second ionisation energy than their first because:
  • when a second electron is removed, stability is being destroyed
  • full electron shells are much harder to break than partially full ones

• the attraction of an atoms nuclei to its bonding electrons
• there are no values for the noble gases as they have no bonding electrons
• general increase across a period because:
  • there is a decrease incovalent radius
  • there is an increase in nuclear charge
  • electrons are held more tightly
• general decrease down a group because:
  • there is an increase in covalent radius
  • the outer electron shells cause a shielding effect
  • generally the electrons are held looser