Past ways of ordering elements:
- Physical/Chemical properties
- Relative atomic mass
1864 - John Newlands tries to arrange elements in his law of octaves. His method is ignored as inconsistencies were found as he progresses.
1869 - Dmitri Mendeleev expands on Newland's Octaves. Gaps are left for undiscovered elements and discovered elements are ordered by atomic mas
Based on electronic structure.
Elements within the same group have similar properties - same amount of electrons in outer shell.
Larger atoms lose electrons more freely, and gain them less freely - due to the electrons in question being further away from the nucleus.
Group 1 - reactivity increases further down the group;the single electron in the outer shell is less attrcted due to the amount of space between electron and nucleus. The atom is lost more freely.
Group 7 - reactivity decreases further down the group; the electron needed to complete the outer shell is less easily attracted due to the weaker attraction.
Group 1 - The Alkali Metals
- Silvery Solids
- Hydroxides dissolve in water to give an alkaline solution
- down group one, the alkali metals become:
- more reactive
- lower bp/mp
- very reactive.
- Lithium, Sodium, Potassium, Rubidium, Caesium and Francium
- one outer electron
- reaction with water produces hydrogen gas
- always form ionic compounds
Group 7 - The Halogens
The halogens become less reactive with higher mp/bp as you go down the group.
Non-metals with coloured vapours:
Flourine - very reactive, poisonous
Chlorine - fairly reactive, poisonous, dense
Bromine - dense poisonous red-brown volatile liquid
Iodine - dark grey crystalline solid or purple vapour
Bond covalantly and ionically
Form +1 ions when bonded with metals
They react with metals to produce salts
The Transition Elements
- Good conductors of heat and electricity
- dense, strong, hard - more so than group 1
- unreactive with water and oxygen
- less reactive than group 1
- colourful compounds
- often make good catalysts
- form more than one ion (+3, +2)