National Chemistry

These notes are for the Scottish National Chemistry course taught in third and fourth year in most Scottish schools.

The notes available here are concise notes. They are NOT to be considered as material to learn from - they are for revision.

 The notes are arranged under the following topics

Unit 1 Reaction Rates and the Periodic Table,

Unit 2    Fuels and Hydrocarbons

Unit 3  Metal Chemistry

Hidden in the summary notes are links to websites offering further explanations, animations or videos

 KEY FACTS 4 & 7 Bonding

4.1  Atoms can be held together by bonds
  same atoms bonded together = element (H2)
  different atoms bonded together = compound (HCl)


substance Bonding melting pt. Structure
metal element metallic HIGH NETWORK
Non-metal element/compound covalent HIGH NETWORK
Non-metal element/compound covalent LOW MOLECULE
Non-metal+metal compound ionic HIGH NETWORK (ionic lattice)

4.3 Low melting point substances exist as molecules - molecules must have covalent 
  bonding brought about by a sharing of pair(s) of electrons between non-metal atoms.

4.4 A diatomic molecule is made from two atoms and can be an element (H2, C2, O2) or compound (CO, HCl)
Naming simple covalent molecules

4.5 Atoms can achieve a stable electron arrangement of a full outer energy level
  (usually 8) by either
(i) losing electrons 2)8)1 loses 1 electron becoming 2)8 -positive metal ion

(ii) gaining electrons 2)7 gains one electron becoming 2)8 -negative non-metal ion
(iii) sharing a pair of electrons to form a covalent bond share a pair of electrons
  = covalent bond (Cl-F)

4.6 Many molecules have a tetrahedral shape
eg CCl4  SiH4 CH4 

   TiCl4  - help! a metal bonded to a non-metal with a covalent molecular structure -
TRUE -there are some com[pounds like this. It has a low melting point and does not conduct electricity so it must be a covalent molecule!

7.1 Ionic bonding
 Metals form positive ions by losing electrons click
Non-metals form ions by gaining electrons (check in data book page 7)
Both form a full outer orbital of electrons - usually 8
See how to write ionic formulae for sodium chloride, calcium oxide, magnesium chloride and calcium phosphide,
See how to write formula using the complex (polyatomic) ions found on page 4


substance conducts when Bonding melting pt. Structure
metal element solid or molten METALLIC HIGH NETWORK
Non-metal element/compound NO COVALENT

metal-Non-metal compound solution or molten IONIC HIGH NETWORK
Noble gas NO 'None' LOW atom

Low melting point = Covalent (bonded) molecule or noble gas

Metals conduct when solid or molten by movement of electrons (electricity in metal wires).
Ionic compounds conduct when molten or in solution when ions can move

In covalent substances the charged particles are never free to move

carbon in the form of graphite is the only non-metal that conducts - used as electrodes.

7.3 Ionic compounds exist as networks (or lattices) of positive ions and negative ions.
Ionic compiunds do not conduct when solid because the ions are held tightly and cannot move.
Ionic compounds can conduct electricity when molten or when in solution because the charged particles, the ions, are free to move.
When the ionic compound dissolves in water the lattice breaks up completely.
Covalent and metallic substances cannot be electrolysed as they do not have positive and negative charges able to move

7.4 A molten ionic compound or ionic solution (aq) which conducts electricity is called an electrolyte.
The passing of electricity through a molten ionic compound or an ionic solution (using diret current) causes the decomposition of the compund into its elements - this is called ELECTROLYSIS.

(Some rervision notes call the electrodes anode and cathode - tghis information is not required by the Scottish syllabus - as far as you are concerned cathode is negative and anode positive

Electrolysis of molten lead bromide
2Br- -----> Br2 + 2e-
Pb2+ +2e -----> Pb

Positive metal ions are attracted to the negative electrode to gain electrons and produce the metal element<BR><BR>
eg. Pb2+ + 2e ----> Pb
Negative non- metal ions are attracted to the positive electrode to lose electrons and produce the non-metal element
eg. 2Br- --------> Br2 + 2e

Electrolysis of copper chloride

7.5 Ion colour migration
Cu2+, the copper(II) ion, is blue. If a copper compound is being electroysed the blue colour would move to the negative electrode.
Eventually brown copper would appear on the electrode as the copper(II) ion gained electrons.<BR>
Cu2+ + 2e --------> Cu

7.6 Covalent substances have covalent bonds produced by a sharing of a pair of elctrons - the electrons in a caovalent substance are held too tightly to move between atoms so electricity cannoy be conducted.
Covalent molecules are usually gases or liquids and always have LOW melting/boiling points.
Generallly covalent substances do not dissolve in water (eg petrol, hydrocarbons) but some can (eg glucose).

7.7 High melting point - network solids - exist because of strong bonds between the atoms linking all of the atoms together.
Low melting point covalent molecules have weak (easily broken) forces between the molecules. (Covalent bonds are just as strong as metallic and ionic bonds.

Ionic and covalent bonding animation

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