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Introduction to Chemistry and Laboratory Apparatus | Week 15 Topics1 Quiz
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Nature of Matter | Week 23 Topics1 Quiz
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Separation Techniques I | Week 31 Topic
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Separation Techniques II | Week 45 Topics1 Quiz
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Particulate Nature of Matter I | Week 55 Topics1 Quiz
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Particulate Nature of Matter II | Week 69 Topics1 Quiz
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Symbols, Formulae & Oxidation Number | Week 77 Topics1 Quiz
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Laws of Chemical Combination | Week 84 Topics1 Quiz
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Chemical Equation & Chemical Combination (Chemical Bonding) I | Week 94 Topics1 Quiz
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Chemical Combination (Chemical Bonding) II | Week 104 Topics1 Quiz
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Chemical Combination (Chemical Bonding) III & Shapes of Covalent Molecules | Week 113 Topics1 Quiz
Topic Content:
- Writing Chemical Formulae
- Oxidation Numbers of Some Elements
- Formulae Containing Radicals
- Acid Radicals
- Oxidation Numbers of Radicals
Compounds are made up of molecules and the formula of a molecule of a compound is combined in correct proportions or valencies.
A chemical formula is defined as a collection of chemical symbol that is used to show the elements present in any compound and its proportion.
Writing Chemical Formulae:
In writing chemical formulae, valencyValency or Valence of an element is a measure of an atom's ability to combine with other atoms to create molecules or chemical compounds. More, 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:
| Element | Symbol | Oxidation Number | Valency |
| Aluminium | Al | +3 | 3 |
| Argon | Ar | Nil or 0 | 0 |
| Barium | Ba | +2 | 2 |
| Bromine | Br | -1 | 1 |
| Calcium | Ca | +2 | 2 |
| Carbon | C | +2 or +4 | 2 or 4 |
| Chlorine | Cl | -1 | 1 |
| Copper | Cu | +1 or +2 | 1 or 2 |
| Gold | Au | +1 | 1 |
| Helium | He | Nil or 0 | 0 |
| Hydrogen | H | +1 | 1 |
| Iodine | I | -1 | 1 |
| Iron | Fe | +2 or +3 | 2 or 3 |
| Krypton | Kr | Nil or 0 | 0 |
| Lead | Pb | +2 or +4 | 2 or 4 |
| Magnesium | Mg | +2 | 2 |
| Mercury | Hg | +1 or +2 | 1 or 2 |
| Neon | Ne | Nil or 0 | 0 |
| Nitrogen | N | -3 or -5 | 3 or 5 |
| Phosphorus | P | -3 or -5 | 3 or 5 |
| Potassium | K | +1 | 1 |
| Silver | Ag | +1 | 1 |
| Sodium | Na | +1 | 1 |
| Sulphur | S | -2 or -4 or -6 | 2 or 4 or 6 |
| Zinc | Zn | +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 |
| Ammonium | NH4+ | +1 |
| Hydroxide | OH– | -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 |
