Equations, chemical formulae and amount of substance

  • Created by: pladoo
  • Created on: 21-10-19 14:42

Equations, chemical formulae and amount of substance – topic 3
Balancing chemical equations

  • A chemical reaction can be represented by a chemical equation.
  • A chemical equation summary in word/symbols the change that is taking place
  • Magnesium reacting with the air
  • Magnesium + oxygen -> magnesium oxide

What information does this give about a reaction?

  • The elements/compounds reacting (reactants) and the product of the reactions (products)
  • The state of the reactants and products
  • Quantities of reactants and products

2Mg(s) + O₂(g) -> 2MgO(s)

This tells a person that Magnesium has two moles and is in a solid state and has an atomic mass of (48g) It also says that it reacts with (32g) of Oxygen to produce (80g) of solid magnesium oxide.

This equation does not tell us about

Energy changes in the reaction

The rate of the reaction

Conditions needed for the reaction.

Rules for writing a chemical equation

  • Write a word equation
  • Write the correct formulas for each reactant and product (O₂, not O as oxygen always comes in pairs.)
  • Check if the formula is balanced if it isn't balanced it, don’t change the small number.


Ion – A charged particle that has lost or gained electrons to fill the outer shell.

Not every element in the periodic table forms an ion, eg. Group 4 and group 8. Group 4 cannot form an ion as it requires too much energy to break the bonds. To create a full outer shell. Group 8 does form an ion as they already have a full outer shell.

Hydrogen and metals form positive ions whilst the non-metals – the hydrogen forms negative ions.



Ions in transition metals

In most cases, transition metals can form more than one type of ion (+/2+/3+), but there are some exceptions, silver only forms Ag+ ions, Zinc only forms Zn2+ and nickel only forms Ni2+.

An example of this is Copper and Iron

Copper can form Cu+ or it can form Cu2+ this can affect a compound as


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