So for the reaction between sodium and water, this is the symbol equation with state symbols: We can add state symbols to a symbol equation to show this: Sometimes it is useful to know whether the reactants and products in a chemical reaction are solids, gases, liquids or dissolved in water. This gives the same number of atoms of each element on each side of the equation. The numbers in front of the formulae are there to balance the equation. So, for sodium chloride the formula is NaCl. The formula for chlorine is `Cl_2`, because the halogens exist as molecules of two atoms ( diatomic molecules ).Įach of the Group 1 halides has a formula with one symbol for the metal and one for the halogen. The formula for sodium is Na - the same as its symbol. This formula shows how many atoms of each element are present. Spectator ion - ion that does not undergo a chemical or physical change during a reaction, but its presence is required to maintain charge neutrality Reactant - substance undergoing a chemical or physical change shown on the left side of the arrow in a chemical equation Product - substance formed by a chemical or physical change shown on the right side of the arrow in a chemical equation Net ionic equation - chemical equation in which only those dissolved ionic reactants and products that undergo a chemical or physical change are represented (excludes spectator ions) Molecular equation - chemical equation in which all reactants and products are represented as neutral substances Balanced equation - chemical equation with equal numbers of atoms for each element in the reactant and productĬhemical equation - symbolic representation of a chemical reactionĬoefficient - number placed in front of symbols or formulas in a chemical equation to indicate their relative amountĬomplete ionic equation - chemical equation in which all dissolved ionic reactants and products, including spectator ions, are explicitly represented by formulas for their dissociated ions