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