AS Chemistry Chapter 1.4 - Bonding

edexcel as chem notes on bonding

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Chapter 1.4 ­ Bonding
Ionic compounds ­ Formed when metals react with non-metals. They are held together by a strong
electrostatic force of attraction between oppositely charged ions. This is called an ionic bond. The
ions are held in a giant lattice structure.
The lattice structure of a particular ionic compound is the arrangement of ions in a particular way
that maximises the attractive forces between oppositely charged ions and minimises the repulsion
between similarly charged ions.
Na - 1s² 2s² 2p
They have the same electronic configuration, so
Ne - 1s² 2s² 2p they are isoelectronic.
The radius of a positive ion is smaller than its elements atomic radius because the remaining
electrons are more strongly attracted to the positive nucleus.
Na Na
Negative ions are larger than the atom that formed them because the additional negative charge
means all the electrons are bound less tightly to the nucleus.
F Fe¯
When you pass x-rays through a crystal, they are scattered or diffracted by the electrons in the
atoms or ions in the structure producing a diffraction pattern known as electron density maps.
Electron density maps show that the exact arrangement of ions in an ionic lattice varies depending
on the relative sizes of the different ions present. ....................................................................................
E.g. In sodium chloride, each ion has 6 nearest neighbours, so the coordination number is 6. It has a
face-centred cubic structure. It forms a rock salt structure. ..................................................................
E.g. Caesium chloride has a coordination number of 8. It has a body-centred cubic structure.
Evidence for the existence of ions:-
Ionic compounds have high melting and boiling points, so this suggests that the particles
that make up ionic substances are held tightly to each other, so they must be positively and
negatively charged to have an attraction and thus make a strong bond.
Ionic compounds can conduct electricity when molten but not when solid. This shows that
when the ionic compound melts, the attraction between the ions is overcome.
In electrolysis the ions are attracted to the oppositely charged ions.

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Lattice Energy ­ Energy released when a lattice is formed. ........................................................................
E.g. Na(g) + Cl¯(g) H lat NaCl¯ (s)
The lattice energies of substances can be calculated by using a Born-Haber cycle...........................
E.g.…read more

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No distortion as the difference in electronegativity is high.
E.g. One ion is much more electronegative than the other.
+ -
The difference in electronegativity between the ions is very
small so there is more polarisation, and they behave partially
like a covalent bond.
The theoretical values are not always correct as it assumes that all ions are spherical and separate,
and that the electrons are evenly distributed across the ion.…read more

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