Metallic bonding
The nature of the metallic bond
The structure of a metallic bond is quite different from covalent and ionic bonds. In a
metallic bond, the valence electrons are delocalised, meaning that an atom's electrons do
not stay around that one nucleus. In a metallic bond, the positive atomic nuclei (sometimes
called the “atomic kernels”) are surrounded by a sea of delocalised electrons which are
attracted to the nuclei (see figure below).
A microscopic model of metals
Definition 1: Metallic bond
Metallic bonding is the electrostatic attraction between the positively charged
atomic nuclei of metal atoms and the delocalised electrons in the metal.
Figure 1: Positive atomic nuclei (+) surrounded
by delocalised electrons (•)
Figure 2: Ball and stick model of copper
Properties of metals
1. Metals are shiny.
2. Metals conduct electricity because electrons are free to move.
3. Metals conduct heat because the positive nuclei are packed closely together and can
easily transfer the heat.
4. Metals have a high melting point because the bonds are strong and a high
density because of the tight packing of the nuclei.
Activity 1: Building models
Using coloured balls (or jellytots) and sticks (or toothpicks) build models of each type of
bonding. Think about how to represent each kind of bonding. For example, covalent
bonding could be represented by simply connecting the balls with sticks to represent the
molecules, while for ionic bonding you may wish to construct part of the crystal lattice.
Do some research on types of crystal lattices (although the section on ionic bonding only
showed the crystal lattice for sodium chloride, many other types of lattices exist) and try to
build some of these. Share your findings with your class and compare notes to see what
types of crystal lattices they found. How would you show metallic bonding?
Exercise 1: Bonding
Problem 1:
Give two examples of everyday objects that contain:
1. covalent bonds
2. ionic bonds
3. metallic bonds
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Answer 1:
Learners can give any reasonable suggestion, some ideas are given below:
a) Graphite in pencils, water, ammonia in cleaning fluid
b) Table salt, chalk, some rocks
c) Metal cutlery, metal jewellry
Problem 2:
Complete the table which compares the different types of bonding:
Covalent
Types of atoms involved
Nature of bond between atoms
Melting point (high/low)
Conducts electricity? (yes/no)
Other properties
Table 1
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Answer 2:
Ionic
Metallic
Covalent
Ionic
Metallic
Types of atoms
Mainly non-
Some non-metals
Metals only
involved
metals
and some metals
Nature of bonds
Sharing of
Transfer of
Delocalisation of
between atoms
electrons
electrons
electrons
Melting point
Low
High
High
No
Only when molten
Yes
(high/low)
Conducts
electricity?
or in solution
(yes/no)
Other properties
Poor
conductor of
Brittle
Malleable, shiny,
ductile
heat
Problem 3:
Complete the table below by identifying the type of bond (covalent, ionic or metallic) in each
of the compounds:
Molecular formula
H2SO4
Type of bond
FeS
NaI
MgCl2
Zn
Table 2
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Answer 3:
Zinc will conduct electricity most effectively as it is metallically bonded which means that it
has a 'sea' of electrons around it. These electrons can move and this allows conduction of
charge.
Problem 4:
Use your knowledge of the different types of bonding to explain the following statements:
1. A sodium chloride crystal does not conduct electricity.
2. Most jewellery items are made from metals.
3. It is very hard to break a diamond.
4. Pots are made from metals, but their handles are made from plastic.
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Answer 4:
a) In a solid ionic substance there are no free electrons and so charge cannot flow.
b) Metals are shiny and malleable. The malleability means that it can be formed into many
shapes. Jewelry is designed to be pretty and attractive and so shiny materials would be
preferred over non-shiny materials.
c) Diamond is covalently bonded. Covalent bonds are very strong bonds and it is hard to
break them.
d) Metal is a good conductor of heat, while plastic is a poor conductor of heat. When you
cook food you need the pot to be a good conductor of heat but the handles should be poor
conductors of heat so that you don't burn yourself.