Atomic structure

• An element is one type of atom that cannot be broken down
• A compound contains 2+ elements chemically combined in fixed proportions
• A mixture contains 2+ compounds not chemically combined
• Niels Bohr - electrons orbit the nucleus at specific distances
• Ernest Rutherford- Alpha scattering experiment
• James Chadwick - neutrons
• Elements are arranged in order of atomic number
• John Newlands

  • Ordered table in order of atomic weight
  • Realised similar properties every eight element [ law of octaves ] but broke down after calcium
• Dmitri Mendeleev

  • Ordered table in order of atomic mass but not strictly
  • Left gaps for elements that had not been discovered
• Metals are elements that form positive ions
• Group 1 [ Alkali metals ]

  • All react with oxygen to form an oxide
  • All react with chlorine to form a white precipate
  • Reactivity increases going down the group
  • One electron on outer shell
• Lithium

  • Oxygen = burns with strongly red tinged flame and produces a white solid
  • Water = fizzes steadily, gradually disappears
  • Chlorine = white powder produces and settles on the side of the container
• Sodium

  • Oxygen = strong orange flame and produces a white solid
  • Water = fizzes rapidly, melts into a ball and disappears quickly
  • Chlorine = bright yellow flame, clouds of white powder settles on container
• Potassium

  • Oxygen = large pieces produce lilac flame, smaller ones make solid immediately
  • Water = lilac flame, disappears very quickly
  • Chlorine = even more reactive than with sodium
• Group 0: [ Noble gases ]

  • Full outer shell except helium
  • No charge
  • Unreactive
  • Boiling points increase going down the group
• Group 7: The Halogens

  • 7 Electrons on outer shell
  • -1 charge
  • Non metals and exist as molecules
  • React with metals to form ionic compounds
  • React with non metals to form covalent compounds
  • Going down the group - boiling and melting point increases and relative molecular mass
  • Reactivity decreases going down because number of shells decreases
  • Decrease in reactivity means a more reactive halogen can replace a less reactive one in an aqueous solution of its salt

  chlorine + potassium bromide —> potassium chloride + bromine
• Properties of transition metals:

  In comparison to group 1….

  • TM are harder and stronger
  • Higher melting points except from mercury and higher densities
  • Much less reactive and don’t react vigorously with oxygen or water