Periodic Table

Periodic Table

The early periodic table
1. Johann Wolfgang Dobereiner
  1. Law of Triads
  2. The middle element has properties that are an average of the other two.
  3. Hydrogen and aluminium = nitrogen
  4. Lithium and potassium = Sodium
2. John Newlands
  1. Law of Octaves
  2. When ordered in atomic mass, the properties of every eighth element seemed similar
  3. - Groups contained elements without similar properties, eg. carbon, titanium, hydrogen -Mixed up metals and non-metals -Didn't leave gaps
Alkali Metals
1. Group 1
  1. Extremely reactive therefore stored in oil so they don't react with oxygen in the air
  2. Reaction with water: Lithium + water -> lithium hydroxide + hydrogen
    1. Observations: -Gas released therefore bubbles formed -Solid (lithium) would dissolve -UI would turn purple
  3. Properties: -Always form ionic bonds -One electron in outer shell, form +1 charge -Low densities + float on water
  4. Down the group: -More reactive -Lower melting and boiling points
Modern Periodic Table
1. Dmitri Mendeleev
  1. Order of atomic mass
  2. Left gaps for undiscovered elements
  3. Elements with similar properties in groups
  4. When the undiscovered elements were found they fitted the table
2. Arranged in atomic number (protons)
3. Arranged by electrons in outer shell - groups which have similar properties
4. Contains noble gases
  1. Unreactive
  2. The structure that other elements gain when reacting
The Halogens
1. Group 7
  1. Uses - Chlorine: to sterilise pools -Iodine: in antiseptics to treat wounds
  2. Properties: -Low melting point -Poisonous -Non-metals
  3. DIATOMIC MOLECULES - Exist in pairs, F2, CL2 etc.
  4. 7 Electrons in outer shell, form a -1 charge called a halide
  5. Reaction with hydrogen: Chlorine + hydrogen -> hydrogen chloride etc.
  6. Reaction with Alkali metals: Chlorine + Potassium -> potassium chloride
  7. More reactive halogens will displace less reactive ones, get less reactive down the group
  8. Low melting point because only small molecules which have weak intermolecular forces
Transition Metals
1. Fairly unreactive - don't react vigorously with H20 or O2
2. Properties: -High density -Used as catalysts -Coloured compounds -ions with more than one charge
3. -Fe2+ -> green -Fe3+ -> red/brown -Potassium chromate -> yellow -Potassium manganate -> purple -Copper sulfate -> blue
- Groups 1,2 and 3 want to lose electrons therefore MORE SHELLS= MORE REACTIVE. -Groups 4,5,6 and 7 need to gain electrons, therefore LESS SHELLS = MORE REACTIVE.
1. -The further from the positive nucleus the weaker the attraction. -As negative/negative repel each other, the more shells, the stronger the repulsion and the easier electrons are to remove

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