N5 Chem | Bonding and Properties of Materials

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Within the National 5 Chemistry course, you will need to know:

Covalent bonding

Covalent bonds form between non-metal atoms.
A covalent bond forms when two positive nuclei are held together by their common attraction for a shared pair of electrons.
Diagrams can be drawn to show how outer electrons are shared to form the covalent bond(s) in a molecule.
7 elements exist as diatomic molecules through the formation of covalent bonds: H2, N2, O2, F2, Cl2, Br2, I2.
The shape of simple covalent molecules depends on the number of bonds and the orientation of these bonds around the central atom. These molecules can be described as linear, angular, trigonal pyramidal or tetrahedral.
More than one bond can be formed between atoms leading to double and triple covalent bonds.
Covalent substances can form either discrete molecular or giant network structures.

Covalent molecular substances:

have strong covalent bonds within the molecules and only weak attractions between the molecules
have low melting and boiling points as only weak forces of attraction between the molecules are broken when a substance changes state
do not conduct electricity because they do not have charged particles which are free to move Covalent molecular substances which are insoluble in water may dissolve in other solvents.

Covalent network structures:

have a network of strong covalent bonds within one giant structure
have very high melting and boiling points because the network of strong covalent bonds is not easily broken
do not dissolve

In general, covalent network substances do not conduct electricity. This is because they do not have charged particles which are free to move.

Ionic compounds

Ions are formed when atoms lose or gain electrons to obtain the stable electron arrangement of a noble gas.
In general, metal atoms lose electrons forming positive ions and non-metal atoms gain electrons forming negative ions.
Ion-electron equations can be written to show the formation of ions through loss or gain of electrons.
Ionic bonds are the electrostatic attraction between positive and negative ions.
Ionic compounds form lattice structures of oppositely charged ions with each positive ion surrounded by negative ions and each negative ion surrounded by positive ions.
Ionic compounds have high melting and boiling points because strong ionic bonds must be broken in order to break up the lattice.
Many ionic compounds are soluble in water. As they dissolve the lattice structure breaks up allowing water molecules to surround the separated ions.
Ionic compounds conduct electricity only when molten or in solution as the lattice structure breaks up allowing the ions to be free to move. Conduction in ionic compounds can be explained by the movement of ions towards oppositely charged electrodes.