Symbols, Formulae and Equations

Chemical Symbols

Each element has a unique chemical symbol, consists of one or two letters from the Latin name of the element.
The first letter is always capitalised and the second (if present) is always lower-case.
For example, Hydrogen is represented as H, Carbon as C, and Oxygen as O.

Chemical Formulae

A chemical formula represents the ratio of atoms of each element in a compound.
The number of atoms of an element in a formula is indicated by a subscript after the chemical symbol. If no number is present, it’s assumed to be 1.
For example, Water (H2O) has two Hydrogen atoms and one Oxygen atom; Carbon Dioxide (CO2) has one Carbon atom and two Oxygen atoms.
Polyatomic ions, groups of atoms that carry a charge, are represented as a unit within the formula, like hydroxide (OH-) in Sodium Hydroxide (NaOH).

Balancing Chemical Equations

Chemical equations represent a chemical reaction showing the reactants and products.
Reactants are on the left side, products are on the right, and they are separated by an arrow (->) which represents the course of reaction.
Balancing a chemical equation means ensuring there is the same number of each type of atom on both sides of the equation, in accordance with the law of conservation of mass.
Balanced chemical equations help in calculations regarding quantities of reactants and products, which is essential for stoichiometry.

State Symbols

State symbols are used in chemical equations to indicate the physical states of the reactants and products.
The four main state symbols are (s) for solids, (l) for liquids, (g) for gases, and (aq) for substances dissolved in water (aqueous solutions).
For example, the reaction of sodium with water can be depicted as: 2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g).

Ionic Equations

An ionic equation includes ions as individual entities and is often used when ions are involved in a reaction in aqueous solution.
In such equations, ions which do not take part in the reaction (spectator ions) can be ignored, leading to a simplified net ionic equation.
For example, the reaction of Ag+(aq) and Cl-(aq) to form AgCl(s) could be represented in a net ionic equation as Ag+(aq) + Cl-(aq) -> AgCl(s).