C2 - periodic table

• before the knowledge of protons, neutrons and electrons, scientists arranged the periodic table by atomic weight.
• in 1869 - mendeleev - Russian scientist published his periodic table. he arranged elements by atomic weight but left gaps for where he predicted elements would be - he accurately predicted the properties of elements that weren’t discovered until years later e.g. gallium
• mendeleev’s periodic table is still diferent from the modern one as some of his masses were wrong due to the existence of isotopes
• what is a metal?

  An element which loses electrons to form a positive charge
• what is a non metal?

  an element which gains electrons to form a negative charge
• what is an ion?

  an element with a positive or negative charge
• group 1 - alkali metals

  • soft, low density
  • react vigorously with water releasing hydrogen
• group 7 - halogens

  • low melting point, exist as a pair
  • react with group 1 metals to form compounds
  • can carry out displacement reactions
• group 0 - noble gases

  • low melting/boiling point
  • 8 electrons in outer shell - except helium
  • unreactive - full outer shell
• Trend of group 1 - alkali metals:

  more reactive as you go down, outermost electron further from the nucleus so its eaiser to lose
• trend of group 7 - halogens:

  higher melting point as you go down the group, less reactive as you go down the group
• trend of group 0 - noble gases:

  higher melting/boiling point as you go down the group - due to increase in density