IB Chemistry home > Syllabus 2016 > Structure and bonding > Properties of metals

Syllabus ref: 4.5

Physical properties of metals are those characteristics that do not involve chemical change. These include the conductivity, hardness, melting point, malleability etc.

Conductivity

All metals are conductors; it is the one characteristic that unites them. To conduct means to pass an electrical current and conductivity is a measure of how well a substance can conduct.

Electricity is a flow of electrons from a negative potential to a positive potential. When an electrical potential is applied to two ends of a metal wire, a metal can pass electrons from atom to atom, due to their delocalised electron layers.

In general, metals that have a high ionic charge, or those that easily release electrons are the best conductors.


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Melting point

The melting point of a metal may be used to assess the strength of its interparticular forces. The melting point is a function of the ionic charge on the metal ions in the lattice and their size (radius).

Example: Explain the difference in melting points between the values for sodium (98ºC) and magnesium (667ºC).

Sodium from group I forms ions with a single plus charge. Each atom only provides 1 electron to the delocalised electron cloud, responsible for holding the ions together.

Magnesium however forms ions with a 2+ charge, each atom providing two electrons to the charge cloud that holds the ions together.

An additional factor increasing the lattice strength of magnesium, is the smaller size of its ion compared to that of sodium. The magnesium 2+ ion has a higher charge density and a greater attractive force for the delocalised electron charge cloud.

There is also a third, more unpredictable factor, which is the actual packing of the metal atoms. Different metals may use one of several different packing schemes, or even a mixture of more than one.


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Malleability

Malleable means the ability to bend and stretch without breaking. Metals are generally malleable and can be shaped into almost any form, or drawn into wires (ductility). The reason lies in the microscopic structure of a metal.

Metallic structures are held together by a sea of electrons. This type of bonding is non-directional, i.e. it doesn't act in any specific direction. Consequently, the shape of a metal can be deformed and the structural integrity is maintained. After deformation, the force of attraction still holds all the ions in their new positions in the structure.


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Other metallic properties

Metals are usually hard, silvery, shiny, sonorous, and have high melting points.

There are of course many exceptions to these general properties. Lead, for example is difficult to polish into a shine. Mercury is a liquid at room temperature and gallium is very nearly so.

The only reliable metallic property is conductivity.


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