Chemical Formula

Key Stage 3

A Chemical Formula is a simple way to show the number and type of atoms in a chemical.

Singular Noun: Chemical Formula

Plural Noun: Chemical Formulae

Chemical Formulae show which elements are in a molecule.

The number of each element in a molecule is shown with a number written just after and lower than the element.

H₂O	CO₂	CH₄	C₂H₅OH

Water has 2 Hydrogen atoms and 1 Oxygen atom.	Carbon Dioxide has 1 Carbon atom and 2 Oxygen atoms.	Methane has 1 Carbon atom and 4 Hydrogen atoms.	Ethanol has 2 Carbon atoms, 6 Hydrogen atoms and 1 Oxygen atom.

A Chemical Formula is a way to show the numbers of atoms of each element in a chemical.

Chemical Formulae show which elements are in a molecule.

The number of each element in a molecule is shown with subscript after that element.

Some chemical formulae are written with the elements at specific points, not all grouped together, to show where different elements are bonded.

CH₃COOH: Ethanoic Acid with two Carbon atoms, two Oxygen atoms and four Hydrogen atoms. This shows that one Carbon is bonded to three Hydrogen atoms while the other Carbon is double bonded to one Oxygen and has a single bond with an Oxygen, which itself it bonded to a Hydrogen.

HCl	H₂SO₄	C₃H₈O	C₃H₈O

Hydrochloric Acid molecules have 1 Hydrogen atom and 1 Chlorine atom.	Sulphuric Acid molecules have 2 Hydrogen atoms, 1 Sulphur atom and 4 Oxygen atoms.	Propanol or Propan-1-ol has 3 Carbon atoms and 8 Hydrogen atoms and 1 Oxygen atom. This has the same chemical formula as Propan-2-ol but a different shape. This may be written with the structural formula CH₃⋅CH₂⋅CHOH to show where the OH group is attached.	Isopropyl Alcohol or Propan-2-ol has 3 Carbon atoms and 8 Hydrogen atoms and 1 Oxygen atom. This has the same chemical formula as Propan-1-ol but a different shape. This may be written with the structural formula CH₃⋅CH₂OH⋅CH₃ to show where the OH group is attached.