properties of metals using the metallic bonding model
Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A
level US grade
9-12 level Revision Notes
Explaining the physical
properties of metals
The giant metallic lattice of metal ions
All metals are lustrous and,
compared to non-metals, most metals are quite dense, hard (tough, high
tensile strength), with high melting/boiling points, though there notable
The strong metallic 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.
The stronger the attraction between the
atoms/ions in the giant metallic lattice, more kinetic energy of the
particles (metal atoms) is
needed to weaken the force between them sufficiently to break the giant
lattice down in melting and eventually sufficiently great enough to overcome the attractive forces to boil the metal.
Energy changes for the physical changes of state
of melting and boiling for a range of differently bonded substances are
compared in a section of
the Energetics Notes.
The strong bonding in metals gives
them a high tensile strength, so alloys like steel are used in building
construction, car bodies etc.
Metals are good conductors of electricity
Why are metals good conductors
Metals are good at conducting electricity because
these 'free' delocalised 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.
Why are metals good conductors
The fact that metals are good at conducting heat 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.
metals, as well as this effect, the 'hot' high kinetic energy electrons move
around freely to transfer the particle kinetic energy more efficiently to
This is a faster process than the transferring heat by the
kinetic energy of atom vibration.
So, where a material needs to be
a good heat conductor, metals quite naturally are used to make everything
from radiators, cooking pans etc.
Its also hand that they are both
strong and high melting when used as a saucepan!
Typical metals also have a silvery surface
but remember this may be easily tarnished by corrosive oxidation in air and
Although many metals will
corrode (oxidise) in the presence of air (oxygen) and water, the strong
bonding prevents them dissolving in water or any other laboratory solvent.
When metals like sodium 'dissolve in water, they do so via a chemical
reaction forming a soluble compound (sodium hydroxide), and do NOT
give a solution of sodium metal.
Unlike ionic and non-metallic element solids, metals are very
malleable - easy to bend or hammer into shape
Why are metals very malleable
and easily bent or pressed shaped?
Metals are be readily bent, pressed or hammered into shape
because the strong bonding is retained even when the metal is stressed (at least
up to a point!).
layers of atoms can slide over each other without fracturing
reason for this is the mobility of the electrons involved in the metallic
When planes of
metal atoms are 'bent' or slide the electrons can run in between the atoms and
maintain a strong bonding situation. This can't happen in ionic solids which
tend to be brittle and the layers of immobile ions fracture easily.
Unfortunately, sometimes a pure metal is
too malleable i.e. to weak for a given purpose, but this problem can be
overcome by alloying the metal with other elements, which are usually metals
too. The resulting alloy can be stronger and tailored to suite a particular
Metals usually have a high density
The strong bonding, particularly when
several electrons are delocalised per atom, draws the metal ions in the
metallic lattice close together, increasing the mass per unit volume i.e.
increasing the density compared to most non-metallic elements.
e.g. densities in g/cm3
(multiply by 1000 to convert to kg/m3)
non-metals: sulfur 2.0; bromine
3.1; carbon 2.25 (graphite) and 3.51 (diamond)
metals: aluminium 2.7 (unusually low);
iron 7.9; gold 19.3
For more on the properties and uses of metals
see Transition Metals and
Industrial Chemistry pages and the note and diagram below.
improved design, problems with fatigue and corrosion
Sub-index: Part 5
Metallic Bonding – structure and properties of metals
bonding and structure notes
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metals be made more useful? (useful links)
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