The periodic table

• Mendeleev’s periodic table

  • Elements were first classified by arranging them in order of increasing atomic weight
  • His periodic table also had gaps
  • Yet he had predicted properties of elements to fill gaps
• Modern periodic table

  • Arranged in order of increasing atomic number
  • periods are horizontal rows
  • groups are vertical columns
  • elements in a group have similar properties
  • the existence of isotopes justifies Mendeleev’s pair rehearsal
• Electronic structure

  • Electrons occupy energy levels also called shells outside of the nucleus
  • first shell, holds up to 2 electrons
  • second shell, holds up to 8
  • third shell, holds up to 8
• Properties of metals

  • In chemical reactions metal atoms lose electrons to form positive ions
  • metals have high melting and boiling points
  • metals conduct heat and electricity
  • most metals have high densities
• Properties of non-metals

  • Some non-metals gain electrons to form negative ions and some non-metal atoms do not form ions at all
  • non-metals have low melting and boiling points
  • Non-metals do not conduct heat
  • most non-metals have low densities