Bonding & Structure in Relation to Properties of Substances

Bonding & Structure in Relation to Properties of Substances

What is Covalent Bonding?

Covalent bonds are formed when non-metal atoms share pairs of electrons with each other.
Each covalently-bonded atom’s outer energy level becomes full, resulting in a stable molecule.
In a covalent bond, the shared electrons are attracted by the nucleus of both atoms, which holds them together.
A dot-and-cross diagram can be used to show the electron arrangement in a covalently bonded molecule.

Properties of Covalent Substances

Substances with covalent bonds can be either simple molecules or giant covalent structures.
Simple molecules are usually gases or liquids with low melting and boiling points due to weak intermolecular forces.
However, they do not conduct electricity as they do not have free electrons or ions.
Giant covalent structures are solids with high melting and boiling points due to strong covalent bonds.

Examples of Covalent Substances

Oxygen (O2): Two oxygen atoms share two pairs of electrons, forming a double covalent bond.
Diamond (C): Every carbon atom forms four single covalent bonds with four other carbon atoms in a tetrahedron structure. It’s an example of a giant covalent structure.
Graphite (C): Each carbon atom forms three covalent bonds with three others, creating layers of hexagonal rings. It’s another example of a giant covalent structure.

Metallic Bonding and its Properties

Metallic bonds are formed when metal atoms share their outermost electrons.
Positive metal ions are arranged in a lattice and the shared electrons are delocalised over the whole structure, known as a ‘sea of electrons’.
Metallic substances are typically shiny, malleable, ductile and good conductors of heat and electricity due to the mobility of the delocalised electrons.

Ionic structures are formed from ions and have high melting points due to strong ionic bonds.
Metallic structures have high melting points and are good conductors due to delocalised electrons.
Simple molecular structures have low melting points due to weak intermolecular forces.
Giant covalent structures have very high melting points due to multiple strong covalent bonds.

Key Understanding Points

Understand the process of electron sharing or transfer in covalent and metallic bonding.
Know the properties of covalent and metallic substances.
Understand the properties of substances with different structures and how these relate to their bonding.
Be able to draw dot-and-cross diagrams to show the electron arrangement in covalently bonded molecules.