Part 5 Metallic Bonding,
Structure and Properties
Brown's Science-Chemistry Chemical Bonding GCSE/IGCSE/AS/A2 O Level Revision Notes
Metallic bonding is described and the properties of metals
are described and explained using the giant metal lattice structure model which
is used to explain the physical properties of metals
Part 1 Introduction - why do atoms bond together? (I
suggest you read 1st)
Ionic Bonding - compounds and properties
Covalent Bonding - small simple molecules and properties
Covalent Bonding - macromolecules and giant covalent structures
Metallic Bonding - structure and properties of metals
Part 6 More advanced concepts for
advanced level chemistry (in preparation, BUT a lot on
intermolecular forces (intermolecular
bonding) in Equilibria Part 8)
- structure and properties of metals
bonding model element/alloys * physical properties of
explain the properties of metals like iron or sodium we need a more
sophisticated picture than a simple particle model of atoms all
lined up in close packed rows and layers.
giant metallic lattice. The
crystal lattice of metals consists of ions (NOT atoms) surrounded by a 'sea of electrons'
forming another type of giant lattice.
- The outer electrons
(-) from the
original metal atoms are free to move around between the positive
metal ions formed (+).
- These free or 'delocalised'
electrons are the 'electronic glue' holding the particles together.
- There is a strong
electrical force of attraction between these free and mobile
electrons (-) and the 'immobile' positive metal ions (+)
and this is the metallic bond.
- Metallic bonding is not
directional like covalent bonding, it is like ionic bonding in the
sense that the force of attraction between the positive metal ions
and the mobile electrons acts in every direction about the fixed
(immobile) metal ions.
Metals can become
weakened when repeatedly stressed and strained. This can lead to
faults developing in the metal structure called 'metal fatigue'
or 'stress fractures'. If the metal fatigue is significant it can
lead to the collapse of a metal structure. So it is important
develop alloys which are well designed, well tested and will last
the expected lifetime of the structure whether it be part of an
aircraft (eg titanium aircraft frame) or a part of a bridge (eg
steel suspension cables).
Explaining the physical
properties of metals
This strong bonding generally results
in dense, strong materials with high melting and boiling points.
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 eg copper
wire in household wiring or electrical appliances.
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
Typical metals also have a silvery surface
but remember this may be easily tarnished by corrosive oxidation in air and
Unlike ionic solids, metals are very
malleable, they can be readily bent, pressed or hammered into shape. The
layers of atoms can slide over each other without fracturing
the structure (see below). The
reason for this is the mobility of the electrons. 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.
For more on the properties and uses of metals
see Transition Metals and Extra
Industrial Chemistry pages and the note and diagram below.
on Alloy Structure
- Shows the regular arrangement of the
atoms in a pure metal crystal and the white spaces show where the free
electrons are (yellow circles actually positive metal ions).
- Shows what happens when the metal is
stressed by a strong force. The layers of atoms can slide over each
other and the bonding is maintained as the mobile electrons keep in
contact with atoms, so the metal remains intact BUT a different
- Shows an alloy mixture. It is NOT a
compound but a physical mixing of a metal plus at least one other
material (shown by red circle), it can be another metal e.g. Ni, a
non-metal e.g. C or a compound of carbon or manganese, and it can be
bigger or smaller than iron atoms. Many alloys are produced to give
a stronger metal. The presence of the other atoms (smaller or
bigger) disrupts the symmetry of the layers and reduces the 'slip
ability' of one layer next to another. The result is a stronger
harder less malleable metal.
- The main point about using
alloys is that you can make up, and try out, all sorts of different
compositions until you find the one that best suits the required
purpose in terms of tensile/compression strength, malleability,
electrical conductivity or corrosion resistance etc.
Revision notes information to help revise KS4 Science
Additional Science Triple Award Separate Sciences GCSE/IGCSE/O level
Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel
GCSE Science/IGCSE Chemistry & OCR 21st Century Science, OCR Gateway Science WJEC/CBAC
GCSE science-chemistry CCEA/CEA GCSE science-chemistry
(and courses equal to US grades 8, 9, 10) basic aid notes for GCE Advanced
Subsidiary Level AS Advanced Level A2 IB Revise AQA OCR Edexcel Salters CIE,
CCEA/CEA & WJEC advanced level courses for pre-university students (equal to US grade 11 and grade 12
and Honours/honors level courses)
WHAT NEXT? - other pages to do with metals
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