Contents
Key Stage 3
Meaning
A Chemical Formula is a simple way to show the number and type of atoms in a chemical.
About 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.
Examples
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. |
Key Stage 4
Meaning
A Chemical Formula is a way to show the numbers of atoms of each element in a chemical.
About Chemical Formulae
- Chemical Formulae show which elements are in a molecule.
- The number of each element in a molecule is shown with subscript after that element.
- MgBr2: Magnesium Bromide with one Magnesium atom and two Bromine atoms.
- CO2: Carbon Dioxide with one Carbon atom and two Oxygen atoms.
- Li2O: Lithium Oxide with two Lithium atoms and one Oxygen atom.
H2SO4: Sulphuric Acid with two Hydrogen atoms, one Sulphur atom and four Oxygen atoms.
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.
Examples
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. The forumula may be written as 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. The forumula may be written as CH3⋅CHOH⋅CH3 to show where the OH group is attached. |