Module 10 Understanding Chemical Reactions

Atoms and Isotopes

• recall that all atoms of the same element have the same number of protons
• recall the relative charges and relative masses of protons, neutrons and electrons
• understand the terms atomic number and mass number
• understand that isotopes are atoms of the same elements with the same number of protons and electrons, but different numbers of neutrons
• calculate the relative atomic mass of an element from relative masses and abundances of its isotopes

Chemical bonds

• recall that some elements combine by means of chemical reactions to form compounds, for example, water, carbon dioxide, sodium chloride and iron sulfide
• recall that an ion is an atom or group of atoms with a positive or negative charge
• recall that ionic bonds are formed between atoms of a metal and a non-metal, for example, sodium and chlorine forming sodium chloride
• recall that chemical bonding involves the transfer or sharing of electrons
• explain the formation of simple ionic compounds (for example, sodium chloride) in terms of transfer of electrons
• describe the structure of ionic compounds as a lattice structure, consisting of a regular arrangement of ions, held together by strong forces between them, forming crystals
• describe and explain the physical properties of giant ionic structures, including sodium chloride and magnesium oxide
• recall that covalent bonds are formed between atoms of some non metals to produce molecules (including hydrogen, nitrogen, oxygen, chlorine and hydrogen chloride)
• explain the formation of simple covalent molecules (e.g. hydrogen, hydrogen chloride, water, methane, carbon dioxide) in terms of shared electrons between non-metal atoms, using dot and cross diagrams
• describe the physical properties of simple molecular compounds
• understand that covalent bond formation can result in simple molecules (e.g. hydrogen, iodine) and giant structures (e.g. diamond and graphite)
• describe and explain the differences between the physical properties of simple molecular substances and those with giant molecular structures

Energy changes

• recall that changes of temperature often accompany reactions
• recall that an exothermic reaction is one in which thermal energy is given out
• recall that an endothermic reaction in one in which thermal energy is taken in
• understand that the breaking of bonds is endothermic and that the making of bonds is exothermic

Using chemical equations

• calculate the relative formula masses of simple compounds, given relative atomic masses
• use chemical equations quantitatively to determine the masses of substances used and produced
• determine the empirical formulae of simple compounds from reacting masses