14- The periodic table

• Groups (vertical)

  • same number of valence electrons
  • elements in the same group have the same type of chemical reactions

  Periods (horizontal)

  • same number of filled electron shells
• Group 17: Halogens

  Group 1: Alkali metals

  Group 18: Noble gases
• metalloids have both metallic and non-metallic properties
• Going down a group

  • increase in metallic properties and decrease in non-metallic properties
  • more reactive (metals), less reactive (non-metals)

  Going down a period

  • metals to non-metals
  • acid-base nature changes from basic to amphoteric to acidic