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Chapter summary

  • A chemical bond is the physical process that causes atoms and molecules to be attracted to each other and held together in more stable chemical compounds.

  • Atoms are more reactive, and therefore more likely to bond, when their outer electron orbitals are not full. Atoms are less reactive when these outer orbitals contain the maximum number of electrons. This explains why the noble gases do not react.

  • Lewis notation is one way of representing molecular structure. In Lewis notation, dots and crosses are used to represent the valence electrons around the central atom.

  • When atoms bond, electrons are either shared or exchanged.

  • Covalent bonding occurs between the atoms of non-metals and involves a sharing of electrons so that the orbitals of the outermost energy levels in the atoms are filled.

  • A double or triple bond occurs if there are two or three electron pairs that are shared between the same two atoms.

  • The valency is the number of electrons in the outer shell of an atom which are able to be used to form bonds with other atoms.

  • Covalent compounds have lower melting and boiling points than ionic compounds. Covalent compounds are also generally flexible, are generally not soluble in water and do not conduct electricity.

  • An ionic bond occurs between atoms where there is a large difference in electronegativity. An exchange of electrons takes place and the atoms are held together by the electrostatic force of attraction between the resulting oppositely-charged ions.

  • Ionic solids are arranged in a crystal lattice structure.

  • Ionic compounds have high melting and boiling points, are brittle in nature, have a lattice structure and are able to conduct electricity when in solution.

  • A metallic bond is the electrostatic attraction between the positively charged nuclei of metal atoms and the delocalised electrons in the metal.

  • Metals are able to conduct heat and electricity, they have a metallic lustre (shine), they are both malleable (flexible) and ductile (stretchable) and they have a high melting point and density.

  • We can work out the relative molecular mass for covalent compounds and the formula mass for ionic compounds and metals.