Ionic, Covalent and Metallic Bonding

• ion

  an electrically charged atom or group of atoms formed by the loss or gain of electrons. The loss or gain of electrons takes place to gain a full outer shell of electrons, which is a more stable arrangement of electrons
• Ionization of metals and non-metals

  • all metals can lose electrons to other atoms to become positively charged ions (cations)
  • all non-metals gain electrons from other atoms to become negatively charged ions (anions)
• ionic compounds

  forms when metal atoms react with non-metal atoms and lose their outer electrons which non-metal atoms gain to form positive and negative electrons. Strong electrostatic forces of attraction between opposing charges hold the electrons together (ionic bond)

  • have a giant lattice structure, the atoms are arranged in an ordering and repeating fashion. Consist of a regular arrangement of alternating positive and negative ions
• properties of ionic compounds

  • usually solid at room temperature
  • high m.p. and b.p due to strong electrostatic forces acting between the oppositely charged ions. The forces act in all directions, and a lot of energy is required to overcome them.
  • good conductors of electricity in the molten state or solution, as they have ions that can move and carry a charge
  • poor conductors in the solid state as the ions are in fixed positions within the lattice and are unable to move
• covalent compounds

  forms when pairs of electrons are shared between atoms; only non-metal elements participate in covalent bonding. When two or more atoms are covalently bonded together, we describe them as 'molecules.'

  • many simple molecules exist in which two adjacent atoms share one pair of electrons a.k.a a single covalent bond (or single bond)
  • if two adjacent atoms share two pairs of electrons, two covalent bonds are formed, a.k.a a double bond
• small molecules

  compounds made up of molecules that contain just a few atoms covalently bonded together.

  • have covalent bonds joining the atoms together
  • intermolecular forces act between neighboring molecules
• Simple molecular compounds

  • Low melting point and boiling point
  • Only weak intermolecular forces acting between the molecules
  • Covalent compounds are usually liquids or gases at room temperature
  • As the molecules increase in size, the intermolecular forces also increase as there are more electrons available, causing the melting point and boiling point to increase
• Electrical conductivity in covalent compounds

  Poor, as there are no free ions or electrons to carry the charge. They do not conduct electricity at all in the solid state and are therefore insulators

  common insulators include:

  • Plastic coating around household electrical wiring
  • Rubber
  • Wood
• allotropes

  different atomic or molecular arrangements of the same element in the same physical state

  • allotropes of carbon is diamond and graphite which have giant covalent structures
  • giant covalent structures contain billions of non-metal atoms, each joined to adjacent atoms by covalent bonds, forming a giant lattice structure
• in a diamond

  • each carbon atom bonds with four other carbons, forming a tetrahedron.
  • all the covalent bonds are identical and very strong
  • no intermolecular forces
  • doesn't conduct electricity
  • very high m.p
  • extremely hard and dense but brittle they can be smashed fairly easily with a hammer
• in graphite

  • each carbon atom is bonded to three others, forming layers of hexagons, leaving one free electron per carbon atom, which becomes delocalized. These free (delocalized) electrons exist in between the layers and are free to move through the structure and carry charge, hence graphite can conduct electricity
  • covalent bonds between the layers are held together by weak intermolecular forces, hence the layers can slide over each other making the graphite slippery and smooth
• uses of graphite

  • pencils
  • as an industrial lubricant, in engines, and in locks
  • also used to make non-reactive electrodes for electrolysis
• silicon (IV) oxide


  a.k.a silicon dioxide or silica (SiO2), is a macromolecular compound that occurs naturally in sand and quartz. Each oxygen atom forms a covalent bond with 2 silicon atoms and each silicon atom in turn forms covalent bonds with 4 oxygen atoms

  • . A tetrahedron is formed with one silicon atom and four oxygen atoms, similar to a diamond.
• SiO2 has lots of very strong covalent bonds and no intermolecular forces so it has similar properties to diamonds.

  • very hard
  • very high boiling point
  • insoluble in water
  • does not conduct electricity
  • is cheap since it is available naturally and is used to make sandpaper and to line the inside of furnaces.
• Metallic bonding

  • Metallic bonding forms a massive metallic lattice, firmly holding together individual metal atoms. Within the metallic lattice, the atoms lose the electrons from their outer shell and become positively charged ions
  • the outer electrons no longer belong to a particular metal atom and are said to be delocalized, they move freely between the positive metal ions like a 'sea of electrons'
  • Metallic bonds are strong and are a result of the attraction between the positive metal ions and the negatively charged delocalised electrons.