Explain how atoms in elements can be rearranged to form new substances.
Recognise the difference between ionic and covalent bonding. Investigate the properties of ionic and covalent substances.
Rearranging Atoms
The law of conservation of mass tells us that the total mass of reactants in a chemical reaction always equals the total mass of the products. This is because atoms are not destroyed in a chemical reaction, they are just rearranged.
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When two elements react together to form a compound, atoms of the different elements combine with each other. For example, when magnesium reacts with chlorine, the magnesium and chlorine atoms bond together to make a new compound called magnesium chloride.
z Fig. 14.3.1
The rearrangement of atoms when hydrochloric acid reacts with sodium hydroxide
Magnesium zz Chlorine Magnesium chloride
When two compounds react, atoms in the reactants are also rearranged to form the new products. For example, the atoms of hydrochloric acid and sodium hydroxide rearrange to form salt and water.
How the atoms of each reactant rearrange to form the products salt and water
Sum of atoms of reactants = 5 Sum of atoms of products = 5
Figures 14.3.1 and 14.3.2 show that the total sum of the atoms in the reactants and the sum of the atoms in the products are the same. As a result, the mass also stays the same.
Chemical Bonds
We know that elements combine with each other to form compounds. To form a compound, the atoms of one element bond with the atoms of other elements.
Compounds form because they are more stable (have lower energy) than the atoms of the elements they are made of.
