SPM Chemistry Form 4 Notes – Terminology and Concepts: Chemical Formulae and Equations (Part 3)

by BerryBerryTeacher

in Berry Reference (Notes)

Berry Berry Easy would like to present all Form 4 SPM student who took chemistry with the third part of the notes on Chemical Formulae and Equations. For those who have missed out on the previous two parts, do check them out and learn about relative atomic mass, relative formula mass, relative molecular mass and the various scales from different atom types, properties (with units) and the very important concept of Standard Temperature and Pressure (s.t.p). So let us begin on the most difficult topic in Form 4 so far, after the earlier easy topics.

SPM Form 4 – Terminology and Concepts: Chemical Formulae and Equations (Part 3)

Empirical and Molecular Formulae

1. Empirical (simplest ratio of atoms of each element that present in the compound) and molecular formulae (actual number of atoms of each element that are present in one molecule of the compound) indicate:

  • the types of the elements
  • the symbols of the elements and the ratio of atoms or
  • moles of atoms of each element in a compound.

2. Molecular formula = (empirical formula)n

n is a positive number

Compound Molecular formula n Empirical formula
Carbon dioxide CO2 1 (CO2) = CO2
Ethane CH3 2 (CH3)2 = C2H6
Propene CH2 3 (CH2)3 = C3H6
Glucose CH2O 6 (CH2O)6 = C6H12O6
Quinine C10H12NO 2 C20H24N2O2

3. Chemical formulae for covalent compounds.

Name Chemical formula Number of each element
Nitrogen gas N2 2 nitrogen atoms
Oxygen gas O2 2 oxygen atoms
Ammonia NH3 1 nitrogen atom and 3 hydrogen atoms
Water H2O 2 hydrogen atoms and 1 oxygen atom

4. Cations are positively-charged ions.

Charge Cations Formula
+1 Ammonium ion NH4+
+1 * Copper(I) ion Cu+
+1 Hydrogen ion H+
+1 Lithium ion Li+
+1 * Nickel(I) ion Ni+
+1 Potassium ion K+
+1 Silver ion Ag+
+1 Sodium ion Na+
+2 Barium ion Ba2+
+2 Calcium ion Ca2+
+2 * Copper(II) ion Cu2+
+2 * Iron(II) ion Fe2+
+2 * Lead(II) ion Pb2+
+2 Magnesium ion Mg2+
+2 * Manganese(II) ion Mn2+
+2 Nickel(II) ion Ni2+
+2 * Tin(II) ion Sn2+
+2 Zinc ion Zn2+
+3 Aluminium ion Al3+
+3 * Chromium(III) ion Cr3+
+3 * Iron(III) ion Fe3+
+4 * Lead(IV) ion Pb4+
+4 * Tin(IV) ion Sn4+

* refer to the Roman numerals

5. Anions are negatively-charged ions.

Charge Anions Formula
-1 Bromide ion Br-
-1 Chloride ion Cl-
-1 Chlorate(V) ion ClO3-
-1 Ethanoate ion CH3COO-
-1 Fluoride ion F-
-1 Hydride ion H-
-1 Hydroxide ion OH-
-1 Iodide ion I-
-1 Manganate(VII) ion MnO4-
-1 Nitrate ion NO3-
-1 Nitrite ion NO2-
-2 Oxide ion O2-
-2 Carbonate ion CO32-
-2 Chromate(VI) ion CrO42-
-2 Dichromate(VI) ion Cr2O72-
-2 Sulphide ion S2-
-2 Sulphate ion SO42-
-2 Sulphite ion SO32-
-2 Thiosulphate ion S2O32-
-3 Nitride ion N3-
-3 Phosphate ion PO43-
-3 Phosphite ion PO33-

6. Chemical formulae for ionic compounds

Name Chemical formula Number of cation Number of anion
Zinc chloride ZnCl2 1 Zn2+ 2 Cl-
Copper(II) sulphate CuSO4 2 Cu2+ 2 SO42-
Aluminium sulphate Al2(SO4)3 2 Al3+ 3 SO42-

7. Meaning of prefixes

Prefix Meaning
Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6
Hepta- 7
Octa- 8
Nona- 9
Deca- 10

8. Naming of chemical (non-metal) compounds with Greek numerical prefixes.

Non-metal compound Chemical formula
Carbon monoxide CO
Carbon dioxide CO2
Sulphur dioxide SO2
Sulphur trioxide SO3
Carbon tetrachloride (tetrachloromethane) CCl4

So, do come back for more Berry Essential Notes. If it is not simplified to its essense, then it is not from Berry Berry Easy. Let us do the summarising while you understand the core before you master the whole topic. Do share out this site with your friends.

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