Chemical Formulae

Chemical Formula

3.3

Chemical Formula

Definition of Chemical Formula

Is a representation of a chemical substance using alphabets to represent the atoms and subscript numbers to show the number of each type of atoms found in the elementary entities of the substance.

Example of Chemical Formula
Name of Compound	Chemical Formula	Number of Each Element in the Compound
Helium	He	One helium atom
Oxygen	\(O_2\)	2 oxygen atoms
Water	\(H_2O\)	2 hydrogen atoms and 1 oxygen atom
Ammonia	\(NH_3\)	1 nitrogen atom and 3 hydrogen atoms
Sulphuric acid	\(H_2SO_4\)	2 hydrogen atoms, 1 sulphur atom and 4 oxygen atoms

Example of the Formation of Chemical Formula

The chemical formula of iron(III) chloride \(FeCl_3\)
- Iron(III) ion = \(Fe^{+3}\)
- Chlorine ion = \(Cl^{-}\)
- Iron, Fe has three positive charges, and Cl has one negative charge.
- When these two types of atoms are reacted together, the charge from both atoms needs to be balanced.
- 3 positive charge from iron needs three negative charges to make the charge equal to zero.
- Since chlorine only has on negative charge; thus, the iron required three chlorine atom to neutralise the three positive charge.
- Therefore the chemical formula would become, \(FeCl_3\).

Formation of Iron(III) ChlorideCompound

The image shows a chemical reaction diagram for the formation of iron(III) chloride (FeCl3). It starts with iron (Fe) with a 3+ charge and chlorine (Cl) with a negative charge. The arrows indicate the combination of Fe and Cl to form FeCl3.

Empirical Formula

Definition of Empirical Formula

The chemical formula that shows the simplest ratio of the number of atoms of each element in a compound.

Steps in Determining the Empirical Formula of a Compound

The diagram shows STEPS IN DETERMINING THE EMPIRICAL FORMULA OF A COMPOUND. 1. Determine the mass of each element. 2. Determine the number of mole. 3. Simplify the number of mol using the same factor. 4. Multiply the number of mole with a factor to get an integer.

Example

Element	C	H
Mass (g)	\(96\)	\(18\)
Number of Moles	\(\dfrac{96}{12}=8\)	\(\dfrac{18}{1}=18\)
Mole Ratio	\(8\)	\(18\)
Simplest Mol Ratio	\(\dfrac{8}{2} =4\)	\(\dfrac{18}{2} = 9\)
Empirical Formula	\(C_4H_9\)

Empirical Formulae of Several Substances
Water	\(H_2O\)
Ammonia	\(NH_3\)
Hydrazine	\(NH_2\)
Propene	\(CH_2\)
Benzene	\(CH\)