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Types of Bonding
Elements in groups 1 (1+ ions), 2 (2+ ions), 6 (2- ions), and 7 (1- ions) bond ionically. Positive and
negative ions are held together using electrostatic attraction, forming a giant ionic lattice. As there
are lots of electrostatic bonds, they are hard to break.
Ions are fixed in position in a solid, so they don't conduct electricity. In a liquid, the ions are free to
move, and they carry a charge. It takes lots of energy to break the large number of ionic bonds, and
so they have high melting points. Ionic compounds tend to dissolve in water, because water
molecules are polar, and tend to pull ions away from the lattice.
Covalent bonding is when electrons are shared. Molecules are held together by strong covalent
bonds. There can also be double bonds (e.g. CO2), and triple bonds (e.g. N2 nitrogen sometimes
forms triple bonds). They have low melting and boiling points, because the covalent bonds do not
need to be broken, only the Van der Waals forces or hydrogen bonds.
Giant covalent structures can also be formed. These are very strong because each atom is bonded to
multiple other atoms (e.g. carbon bonds with 4 other carbon atoms). This means 4 bonds need to be
broken to release a single carbon atom.
Graphite is a bit strange, because it is formed from sheets of hexagons with delocalised electrons.
This means that it can conduct electricity. The sheets are quite a long way apart (relative to covalent
bonds), and so it has a low density. Also, because the sheets are only held together using weak Van
der Waals forces, they can slide around (for use in dry lubricant), and be removed using cellotape.
Metals have giant structures the outermost shell of electrons in a metal atom is delocalised. This is
why metals conduct electricity, and heat (the delocalised electrons pass kinetic energy to each
other). Electrons act like glue, sticking the (positive) ions together. Therefore, the number of
delocalised electrons per atom affects the melting point. The more electrons there are, the more
"glue" there is, and so the higher the melting point.
Because there are no bonds, metals are malleable and ductile. The ions simply slide around (with
electrons). They are also insoluble, except in liquid metals, due to the strength of the electrostatic
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