physical properties

• Number of protons

  From left to right along each period, the number of protons increases.  Protons are positively charged, so the nuclear charge increases
• Shielding - number of electrons between the nucleus and outer energy level
• Shielding down a group

  • as move down, more energy levels, so more electron shielding
• Shielding across a period

  no change in shielding
• Atomic radius across a period

  • Atomic radius is distance between nucleus and the outer electron
  • atoms become smaller
• Down a group,

  • atoms become larger
  • The number of electrons and shells increases, so the amount of shielding increases.