BONDING IN METALS
Bonding in metals
Metal atoms have relatively few electrons in their outer shells. When they are packed together, each metal atom loses its outer electrons into a ‘sea’ of free electrons (or mobile electrons).
Having lost electrons, the atoms are no longer electrically neutral.
They become positive ions because they have lost electrons but the number of protons in the nucleus has remained unchanged.
Therefore the structure of a metal is made up of positive ions packed together.
These ions are surrounded by electrons, which can move freely between the ions.
- An ion is a charged particle made from an atom by the loss or gain of electrons.
- Metal atoms most easily lose electrons, so they become positive ions. In doing so they achieve a more stable electron arrangement, usually that of the nearest noble gas.
These free electrons are delocalized (not restricted to orbiting one positive ion) and form a kind of electrostatic ‘glue’ holding the structure together.
In an electrical circuit, metals can conduct electricity because the mobile electrons can move through the structure carrying charge.
His type of bonding (called metallic boding) is present in alloys as well. Alloys, for example solder and brass, will conduct electricity.
The physical properties of metals:
This strong bonding generally results in dense, strong materials with high melting and boiling points.
Usually a relatively large amount of energy is needed to melt or boil metals.
- Metals are good conductors of electricity because these ‘free’ electrons carry the charge of an electric current when a potential difference (voltage!) is applied across a piece of metal.
- Metals are also good conductors of heat. This is also due to the free moving electrons.
Non-metallic solids conduct heat energy by hotter more strongly vibrating atoms, knocking against cooler less strongly vibrating atoms to pass the particle kinetic energy on.
In metals, as well as this effect, the ‘hot’ high kinetic energy electrons move around freely to transfer the particle kinetic energy more efficiently to ‘cooler’ atoms.
- Typical metals also have a silvery surface but remember this may be easily tarnished by corrosive oxidation in air and water.
- Unlike ionic solids, metals are very malleable, they can be readily bent, pressed or hammered into shape.