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SS1: CHEMISTRY - 1ST TERM

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  1. Introduction to Chemistry and Laboratory Apparatus | Week 1
    5Topics
    |
    1 Quiz
  2. Nature of Matter | Week 2
    3Topics
    |
    1 Quiz
  3. Separation Techniques I | Week 3
    1Topic
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    1 Quiz
  4. Separation Techniques II | Week 4
    5Topics
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    1 Quiz
  5. Particulate Nature of Matter I | Week 5
    5Topics
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    1 Quiz
  6. Particulate Nature of Matter II | Week 6
    9Topics
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    1 Quiz
  7. Symbols, Formulae & Oxidation Number | Week 7
    7Topics
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    1 Quiz
  8. Laws of Chemical Combination | Week 8
    4Topics
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    1 Quiz
  9. Chemical Equation & Chemical Combination (Chemical Bonding) I | Week 9
    4Topics
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    1 Quiz
  10. Chemical Combination (Chemical Bonding) II | Week 10
    4Topics
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    1 Quiz
  11. Chemical Combination (Chemical Bonding) III & Shapes of Covalent Molecules | Week 11
    3Topics
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    1 Quiz
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Compounds are made up of molecules and the formula of a molecule of a compound combined in correct proportions or valencies.

Writing Chemical Formulae

In writing chemical formulae, valency, which can be regarded as oxidation numbers, will be considered. 

Valency is the combining power of an element.

The metals exhibit positive valency (oxidation number) because they give out electrons while non-metals exhibit negative valency (oxidation number) because they accept electrons.

Oxidation Numbers of Some Elements

ElementSymbolOxidation Number Valency
AluminiumAl+3      3
ArgonArNil or 0      0
BariumBa+2      2
BromineBr-1      1
CalciumCa+2      2
CarbonC+2 or +4  2 or 4
ChlorineCl-1      1
CopperCu+1 or +2  1 or 2
GoldAu+1      1
HeliumHeNil or 0      0
HydrogenH+1      1
IodineI-1      1
IronFe+2      2
KryptonKrNil or 0      0
LeadPb+2 or +4    2 or 4
MagnesiumMg+2        2
MercuryHg+1 or +2    1 or 2
NeonNeNil or 0      0
NitrogenN-3 or -5    3 or 5
PhosphorusP-3 or -5    3 or 5
PotassiumK+1      1
SilverAg+1      1
SodiumNa+1      1
SulphurS-2 or -4 or -62 or 4 or 6 
ZincZn+2        2

Formulae Containing Radicals

A radical is a group of atoms of two or more elements carrying a positive or negative charge.

E.g NH4+, OH, NO3, CO32-

Acid Radicals

Acid Radicals are radicals derived from acid e.g SO42- Tetroxosulphate (VI) ion derived from H2SO4.

ClO3 – Trioxochlorate (V) ion derived from HClO3.

The only basic radical is Ammonium ion (NH4+) derived from NH4CL or NH4NO3.

Oxidation Numbers of Radicals

Radical Formula Oxidation Number 
AmmoniumNH4++1
HydroxideOH-1
Trioxonitrate (V)NO3-1
Dioxonitrate (III)NO2-1
Trioxocarbonate (IV)CO32--2
Hydrogen trioxocarbonate (IV)HCO3-1
Trioxochlorate (V)CLO3-1
Tetraoxomanganate (VII)MnO4-1
Tetraoxosulphate (VI)SO42--2
Tetraoxochromate (VI)CrO4-2-2
Trioxophosphate (III)PO33--3
Tetraoxophosphate (V)PO43--3
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