Changes

| style="height:20px; width:200px; text-align:center;" |'''C₂H₅OH'''|-|[[File:BallandStickWater.png|center|200px]]|[[File:BallandStickCarbonDioxide.png|center|200px]]|[[File:BallandStickMethane.png|center|200px]]|[[File:BallandStickEthanol.png|center|200px]]|-| style="height:20px; width:200px; text-align:center;" |[[Water]] has 2 [[Hydrogen]] [[atom]]s and 1 [[Oxygen]] [[atom]].| style="height:20px; width:200px; text-align:center;" |[[Carbon Dioxide]] has 1 [[Carbon]] [[atom]] and 2 [[Oxygen]] [[atom]]s.| style="height:20px; width:200px; text-align:center;" |[[Methane]] has 1 [[Carbon]] [[atom]] and 4 [[Hydrogen]] [[atom]]s.| style="height:20px; width:200px; text-align:center;" |[[Ethanol]] has 2 [[Carbon]] [[atom]]s, 6 [[Hydrogen]] [[atom]]s and 1 [[Oxygen]] [[atom]].|} ==Key Stage 4=====Meaning===A [[Chemical Formula]] is a way to show the numbers of [[atom]]s of each [[element]] in a [[chemical]]. ===About Chemical Formulae===: '''Chemical Formulae''' show which [[element]]s are in a [[molecule]].: The number of each [[element]] in a [[molecule]] is shown with subscript after that [[element]].: Some '''chemical formulae''' have brackets which indicate that the [[element]]s in the bracket are multiplied by the number after the bracket.*MgBr₂: [[Magnesium Bromide]] with 1 [[Magnesium]] [[atom]] and 2 [[Bromine]] [[atom]]s.*CO₂: [[Carbon Dioxide]] with 1 [[Carbon]] [[atom]] and 2 [[Oxygen]] [[atom]]s.*Li₂O: [[Lithium Oxide]] with 2 [[Lithium]] [[atom]]s and 1 [[Oxygen]] [[atom]].*Al(OH)₃: [[Aluminium Hydroxide]] with 1 [[Aluminium]] [[atom]], with 3 lots of OH; 3 [[Oxygen]] [[atom]]s and 3 [[Hydrogen]] [[atom]]s.*Al₂(CO₃)₃: [[Aluminium Carbonate]] with 2 [[Aluminium]] [[atom]]s, and 3 lots of CO₃; 3 [[Carbon]] [[atom]]s and 9 [[Oxygen]] [[atom]]s. Some '''chemical formulae''' are written with the [[element]]s at specific points, not all grouped together, to show where different [[element]]s are [[Chemical Bond|bonded]]. This is called a [[Structural Formula|structural formula]].*CH₃COOH: [[Ethanoic Acid]] with 2 [[Carbon]] [[atom]]s, 2 [[Oxygen]] [[atom]]s and 4 [[Hydrogen]] [[atom]]s. This shows that one [[Carbon]] is [[Chemical Bond|bonded]] to three [[Hydrogen]] [[atom]]s while the other [[Carbon]] is [[Double Bond|double bonded]] to one [[Oxygen]] and has a [[Single Bond|single bond]] with an [[Oxygen]], which itself it bonded to a [[Hydrogen]].*CH₃CH₂COOH: [[Propanoic Acid]] with three [[Carbon]] [[atom]]s, two [[Oxygen]] [[atom]]s and 6 [[Hydrogen]] [[atom]]s. ===Examples==={| class="wikitable"| style="height:20px; width:200px; text-align:center;" |'''HCl'''| style="height:20px; width:200px; text-align:center;" |'''H₂SO₄'''| style="height:20px; width:200px; text-align:center;" |'''C₃H₈O'''| style="height:20px; width:200px; text-align:center;" |'''C₃H₈O'''|-|[[File:BallandStickHydrochloricAcid.png|center|200px]]|[[File:BallandStickSulphuricAcid.png|center|200px]]|[[File:BallandStickPropanol.png|center|200px]]|[[File:BallandStickPropan-2-ol.png|center|200px]]|-| style="height:20px; width:200px; text-align:center;" |[[Hydrochloric Acid]] [[molecule]]s have 1 [[Hydrogen]] [[atom]] and 1 [[Chlorine]] [[atom]].| style="height:20px; width:200px; text-align:center;" |[[Sulphuric Acid]] [[molecule]]s have 2 [[Hydrogen]] [[atom]]s, 1 [[Sulphur]] [[atom]] and 4 [[Oxygen]] [[atom]]s.| style="height:20px; width:200px; text-align:center;" |[[Propanol]] or [[Propan-1-ol]] has 3 [[Carbon]] [[atom]]s and 8 [[Hydrogen]] [[atom]]s 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|structural formula]] '''CH₃CH₂CH₅₂OH'''to show where the OH group is attached.| style="height:20px; width:200px; text-align:center;" |[[Isopropyl Alcohol]] or [[Propan-2-ol]] has 3 [[Carbon]] [[atom]]s and 8 [[Hydrogen]] [[atom]]s 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|structural formula]] '''CH₃CHOHCH₃''' to show where the OH group is attached.