Chemical Bonding
Chemical bonding is the start of all things great
atom is now ‘feeling’ more positive without that
and small. The ways in which atoms and
electron.
molecules bond together can determine how they
behave in different environments. Take table salt
and methane, for example.
If we consider these materials at a basic level
Chlorine, on the other hand, likes to take on other
electrons, having a ‘desire’ to do so. When
sodium donates its electron to chlorine, they form
an attraction force.
their bonding is very different. Sodium chloride
consists of positively charged Na+ ions and
negatively charged Cl- ions held together. This
attraction is known as ionic bonding and
describes the force in which opposite charges
attract, like magnets. Magnets have no literal
bond holding them together. In the same way
ionically bonded materials are not literally bonded
together but are held together by this attractive
force.
The diagram above shows how sodium gives its
electron to chlorine and forms the bonding force
between them. You may be familiar that table salt
is a crystal. This crystal character is a result of
the ionic bonding (attractive force) between the
Na and Cl over a larger lattice structure.
Methane is a covalently bonded material. This
bonding involves atoms sharing the electrons
they hold between them. We’ll discuss this
concept later on.
If it was possible to see the individual Na and Cl
atoms you’d see they look like the diagram
Back to table salt. Sodium (Na), being a metal,
above. This lattice is a large and heavy structure
likes to bond in a certain way. It feels a need to
which means that it is relatively heavy. This
lose an electron in order to bond. If you don’t
heavy nature of the substance prevents it from
know what an electron is have a look at “Atoms,
melting (going from solid to liquid) and
elements and isotopes”.
evaporating (liquid to gas) at lower temperatures.
The electron is given to chlorine to create the
Ionic and covalent bonding are very different. As
ionic bond. As electrons are negatively charged,
mentioned, covalent bonds share the electrons
when they are lost from the atom, they imbalance
directly between the respective atoms. Whereas,
the charge on the atom. This means that the
in ionic bonding, one of the atoms has gained an
electron
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and the other has lost one. Creating the attractive
You’ll probably recognise methane as a gas. We
force.
tend to find covalently bonded materials in all
Metals are bonded in a similar way to ionically
three states (solids, liquids and gases).
bonded materials. The difference being that the
attraction isn’t just felt between neighbouring
atoms but is felt over a larger number of atoms.
This delocalisation of bonding allows the
electrons to flow over the larger bonding area.
The conductive character of metals is created by
this delocalisation of electrons.
Conversely we typically see ionically bonded
materials as solids. This is because they form
materials which are large and heavy at a
molecular level. This means that they typically
have lower vapour pressures.
Definition:
Vapour pressure: the pressure exerted by a
vapour directly above its liquid as a result of
evaporation.
Covalent bonding, on the other hand, is more
Substances with lower vapour pressures don’t
common in non-metals, like methane. The atoms
tend to evaporate quickly. In the context of a
in methane, if you’re not familiar are carbon and
hazmat response, this means that a leak/ spill, of
hydrogen. You can see in the diagram below the
an ionically bonded substance, won’t spread
sharing of electron character of covalent bonding.
through lots of vapours being created- without
Each electron (blue and red) is shared by both
input from external factors. Conversely,
the hydrogen and the carbon.
covalently bonded substances are more likely to
evaporate; typically having a higher vapour
pressure.
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