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Shapes of Molecules & Ions

Polar Bonds & Polar Molecules

Electronegativity is the measure of the pull of an atom of an element on the shared electrons in a covalent bond. In a

polar bond, the shared electrons are drawn towards the more electronegative atom.

Covalent bonds in HCl are polar, as there is only one bond in each molecule, the molecules are also polar. There are

however molecules with polar bonds that are not polar. One example is tetrachloromethane. The four polar bonds in

CCl are arranged symmetrically around the central carbon atom, so that overall they cancel each other out.

Intermolecular Forces

Solubility

Potassium Nitrate Copper (II) Sulphate Calcium Hydroxide Iron (III) oxide

Ammonia, Hydrogen Chloride Sulfur Dioxide Carbon Dioxide Helium

Three reactions are involved, intermolecular forces between solute molecules/solvent molecules/solute & solvent

molecules.

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Hydrocarbons dissolve in non-polar liquids such as cyclohexane because all the intermolecular forces involved are

London forces. However they cannot dissolve in water because of the strong hydrogen bonding between water

molecules, these act as a barrier which keeps out molecules that cannot themselves form hydrogen bonds.

The two liquids ethanol and water are miscible. Alcohols with longer hydrogen chains do not mix with water so

easily. The longer the chain is the less miscibility of the alcohol with water.

RedoxDisproportionation reactions

Warming of Copper (I) oxide with dil.Sulfuric acid:

CuO(s) + HSO(aq) CuSO(aq) + Cu(s) + HO(l)

Some of it is oxidised to Copper (II), while the rest is reduced to Copper(0)

Groups in the Periodic Table

Sodium and Potassium compounds are widely used as chemical reagents. This is due to the fact that the ions of

these alkali metals are unreactive. So they act as spectator ions which do not take part in reactions when the

reagents are used. A second reason is that most Na & K compounds are soluble in water, including their hydroxides

and carbonates. A third reason is due to the colourless nature of the alkali metals in aqueous solutions, so they do

not interfere with colour changes. Na or K compounds are coloured only if the negative ions are coloured.

Potassium Chromate(VI), for example is yellow because CrO ions are yellow.

Thermal stability of carbonates and nitrates

Thermal stability is determined by:

The charge of the metal ions The size of the metal ions

G2 carbonates and nitrates are generally less stable than G1, this suggests that the larger the charge on the metal

ion, the less stable the compounds. The carbonates become more stable down both G1 and G2, this suggests that

the larger the metal ion, the more stable the compounds.

G2 carbonates except Beryllium Carbonate, are thermally stable at room temperature but become unstable as the

temperature rises. The key factor is the energy released as the ions get closer to each other. This is greater when the

metal ion is small than the metal ion is large, and this explains why MgCO decomposes more easily than BaCO

Halogens in oxidation states +1 & +5

When Chlorine dissolves in water, it reacts reversibly forming a mixture of weak Chloric(I) acid & strong Hydrochloric

acid. This is an example of a disproportionation reaction.

HO(l) + Cl(g) HOCl(aq) + HCl(aq)

Bromine reacts in a similar way but to a much lesser extent. Iodine is insoluble in water.

When Chlorine dissolves in Na or K OH solution at room temperature, it produces Chlorate(I) and Chloride ions.

HO(l) + Cl(g) HOCl(aq) + Cl(aq) + H(aq)

On heating, the Chlorate(I) ions disproportionate to Chlorate(V) & Chloride ions. 3ClO(aq) ClO(aq) + 2Cl(aq)