1.5 Symbols, Formulae and Equations 🔣

Chemical symbol

represents element in periodic table with one or two letters, first being capital

Interpreting formula

subscript refers to number of element before

Formula with brackets

multiply atoms inside with subscript outside

Ion charge/ valency

• Group 1: +1

• Group 2: +2

• Group 3: +3

• Group 4: ±4

• Group 5: -3

• Group 6: -2

• Group 7: -1

• Group 8: 0

Working out formula (swap and drop)

• write elements down with their charge/ valency

• swap their numbers

• write formula

Word equations

reactants → products

Metal + oxygen →

Metal oxide

Metal + cold water →

metal hydroxide + hydrogen

Metal + steam →

metal oxide + hydrogen

Metal + acid →

salt + hydrogen

Base + acid →

salt + water

Metal carbonate + acid →

salt + water + carbon dioxide

Metal carbonate →(heat)

metal oxide + carbon dioxide

Hydrocarbon fuel + oxygen →

carbon dioxide + water

Chemical reaction

rearranging atoms (reactants) to make new chemicals (products)

Conservation of mass

no atoms are lost or made but are rearranged, mass products = mass reactants

Balancing symbol equations

elements must have equal numbers of atoms on both sides

Writing balanced symbol equations

• write out equation

• count atoms on each side

• add more until they are equal

• write the amount as coefficient (big number)

(s)

solid

(l)

liquid

(g)

gas

(aq)

aqueous solution (dissolved in water)

Ionic equations

only shows ionic compounds which react, leaving out spectator ions

Neutralisation ionic equation (will always be the same)

H⁺(aq) + OH^-(aq) → H₂O(l)

Displacement ionic equation

remove ions which do not react (one that switches)

Half equations

shows change of atom/ molecule into ion

Writing half equations

• write balanced reactant and product

• write their charges

• balance them by adding electrons

Common compounds

formula must be memorised as may not be given

Water

H₂O

Carbon monoxide

CO

Carbon dioxide

CO₂

Sulfur dioxide

SO₂

Nitrogen monoxide

NO

Nitrogen dioxide

NO₂

Ammonia

NH₃

Methane

CH₄

Hydrochloric acid

HCl

Nitric acid

HNO₃

Sulfuric acid

H₂SO₄

Sodium hydroxide

NaOH

Potassium hydroxide

KOH