Periodicity and trends

• A period is a row in the periodic table.
• A group is a column in the periodic table.
• • Atomic radius decreases along a period.
  • This is because the number of protons in the nucleus increases across the period.
  • As you add protons, you also add electrons. But these are all being added to the same shell, so this does not affect the radius.
  • So each electron feels a stronger attraction to the nucleus and is held closer.
• • Sulfur has a greater nuclear charge than phosphorus because it has more protons.
  • This pulls the electrons closer.
  • This means the atomic radius is smaller.
• Atomic radius increases down a group.

  • This is because the number of electron shells increases down a group.
  • Each subsequent electron shell is further from the nucleus.