1864 - John Newlands, octaves.
1869 - Dimitri Mendeleev expanded on Newlands, Left gaps for undiscovered elements. Ordered by atomic mass.
Elements in same group have sililar properties, same electrons on outer shell.
Larger atoms lose electrons more easily - Smaller atoms lose electrons less easily.
They are all silvery solids, are very reactive and have 1 electon on outer shell.
As you go down the group 1, the alkali metals become;
- Bigger atoms
- More reactive
- Highier density
- Lower boiling point
- Lower melting point
Always form ionic compounds.
Reaction with water produces hydrogen gas.
As you go down group 7, they become;
- Less reactive
- Highier melting point
- Highier boiling point
They are all non-metals with coloured vapours.
Flourine - Very reactive - Yellow gas
Chlorine - Fairly reactive - Green gas
Bromine - Red/Brown volitile liquid
Iodine - Purple vapour
They all form molecules which are pairs of atoms.
They do both ionic and covalent bonding.
They form 1- ions when they bond with a metal.
When they react with a metal they form a salt.
Most reactive halogens will displace less reactive ones.
They all have same properties in common;
- Good conducters of heat and electricity
- Very dense, strong and shiny
- Less reactive than group 1 metals
- Don't react much with oxygen or water.
- Much denser, harder and stronger than group 1 metals.
Transition elements often have more than one ion e.g. Fe2+
Compounds are usually very colourful.
Transition metals and their compounds make good catalysts.
Acids and Alkalis
When acids dissolve in water they produce hydrogen ions H+
When alkalis dissolve in water they produce hydroxide ions OH-
Acids are proton donors.
Alkalis are proton acceptors.
Stronger the acid the lower the PH.
They are used to find out concerntrations.
Allow you to find out exactly how much acid is needed to neutralise a quantity or alkali.
Strong acid + Strong alkali = Any indicator suitable
Weak acid + Strong alkali = Phenophthalein
Strong acid + Weak alkali = Methyl orange
Pipette used to measure out a fixed volume of the soloution.
Burette used to measure the volume of the soloution added.
No. of moles = concerntration x volume
Concerntration = number of moles / volume
Hard water is created by the dissolving action of water.
Temporary hard water is created when rainwater reacts with limstone.
Permanent hard water is created by the dissolving of other ions.
Hard water is created by CaSO4, CaCl2, MgSO4, MgCl2
The following methods are used to remove hard water;
- Boiling...temporary hard water only
- Distillation...removes all types of hardness
- adding washing soda...removed Mg2+ and replaces with sodium
Water can be softened by removing the Calcium and Magnesium ions using an ion-exchange collum.
Scale - CaCO3, Scum - Calcium or Magnesium stearate.