Conductivity• A Conductor is a substance that allows

electricity to pass through it.

• An Insulator is a substance that will not allow electricity to pass through it.

An Electric current is a flow of electrons through a Solid

An Electric current is a flow of Ions through a Liquid

Conductivity and Bonding

• There are three main types of Bonding we shall consider here: `

1.Metallic2.Ionic

3.Covalent.

• Metallic Bonding:This can be regarded as metallic atoms which are so close to each other that their outer electrons can move freely between atoms hence causing an electric current.

• All METALS Conduct electricity

Conductivity and Ionic Bonding

• Ionic Bonding: Occurs between Metal and Non-Metal atoms.

+ = Na+ion - =Cl-ion

When in solid form an Ionic Compound arranges itself in a special structure called

a Lattice

An Ionic compound conducts

Electricity when Molten or in

Solution since the Lattice is broken down

and the Ions are free to

moveIonic compounds do not Conduct when Solid since the Ions are not free to move

Conductivity and Covalent Bonding

• Covalent Bonding: Occurs between non-metal Atoms

• Covalent substances contain no Ions and therefore do not conduct electricity when solid , molten or in solution.

• Carbon(in the form of Graphite) is an exception to the above rule. It has a special type of Covalent Bonding called a Covalent Network.

ElectrolysisElectrolysis• Electrolysis is the passing of an Electric

current through a substance so that it breaks up at each Electrode

-ve.electrode +ve.Electrode

Electrolysis of Copper Chloride

6 volt dc.power

supply.It has to be a dc.current

so that the current flows only in one direction

Electrodes are made of graphite which are good

conductors but don’t easily take part in the reaction

Electrolysis explained

+ve electrode -ve electrode

Cl-

Cl-

Cl-

Cu2+

Cu2+

Cu2+

Copper metal is formed here

Bubbles of Chlorine gas are formed here

The diagram below is a result of the fact that

opposite charges attract.On reaching each electrode they lose or gain electrons and become Elements in their natural form

Ion Electron Half-Equations

• At the -ve electrodeCu2+ ions receive two

electrons and change to Cu metal.Since they gain electrons we say that they have been REDUCED.ie Reduction takes place at the –ve electrode.

• At the +ve electrodeCl- ions lose an electron

and change to Cl atoms.We say that they have been OXIDISED. Now since chlorine is Diatomic it waits for another Ion to do the same so that it can be given off as Cl2

molecules(gas) .Oxidation takes place at the +ve electrode

Cu2+ + 2e Cu Reduction

2Cl- Cl2 + 2e Oxidation

To get the Redox or Ionic Equation we simply “ADD” the Oxidation and Reduction Equations together

Cu2+ + 2e Cu Reduction 2Cl- Cl2 + 2e Oxidation

Cu2+ + 2Cl- Cu +Cl2 IONIC

Solubility

• The rule for SOLUBILITY is that:

Like dissolves Like dissolves LikeLike

This means that the Substance you are trying to dissolve must have the same type of Bonding as the liquid you are trying to Dissolve it in.

eg Covalent substances dissolve in Covalent liquids Ionic substances dissolve in Ionic liquids Note: most Ionic substances also dissolve in water

Melting Points and Boiling Points• Ionic substances when Solid, exist in very stable structures

called Lattices which form strong Ionic bonds between positive and negative Ions. Therefore to break these up we require a lot of Energy and hence the Melting Pts and Boiling Pts. are high.

• Covalent substances have weaker bonds than Ionic substances and have only very weak bonds between molecules(called Van der WaalsVan der Waals forces).As a result not as much energy is required to break up these substances and hence Melting Pts and Boiling Pts.are low. An exception to this rule is Covalent NetworksCovalent Networks,such as, Graphite and Silicon Dioxide who form large stable structures which are difficult to break up and therefore have High Mpts.&Bpts

Colour of IonsColour of Ions• Whilst most Ions are colourless, some are

brightly coloured:

• eg.Cu2+

Ni2+

Dichromate

Permanganate

ChromateWhen these Ions form a compound with another colourless Ion then the compound will be the colour of the coloured Ion.When two coloured Ions join, the compound is a mixture of the two of the two colours

eg.Copper Chromate is Green