Covalent Substances

Covalent Substances 

 When atoms of non-metallic elements combine together they often share elecrons between them.

When an atom of hydrogen, H, and an atom of chlorine, Cl, combine to form hydrogen chloride, HCl, the atoms come close enough together for their outer electron (valence) shells to overlap. This can be represented by the diagram below:

In this way, the shared region of the electron shells bonds the two nuclei together.

In the above example of hydrogen chloride, the shared region of electron shells contains two electrons; one electron was supplied by the hydrogen atom, the other by the chlorine atom. A bond formed in this way is called a CONVALENT BOND. Hydrogen chloride is a COVALENT COMPOUND.

Since the new particle formed is a molecule, hydrogen chloride is described as being a SIMPLE MOLECULAR COMPOUND. Its structure is said to be SIMPLE MOLECULAR because it consists of individual molecules.

The bonding in hydrogen chloride can be represented bya dot-and-cross diagram: 

Simple Molecular Substances

Both elements and compounds can exist as simple molecular substances.

The elements hydrogen, fluorine, chlorine, bromine, iodine, oxygen and nitrogen all exist as DIATOMIC MOLECULES under normal conditions. ('Diatomic' means that the molecule containsTWO atoms).

The dot-and-cross diagrams for these molecules are as shown below: 

Notice that the dot-and-cross diagrams for the F2+, Cl2+, Br2 and I2 molecules are identical. THis is because they belong to the same group of elements, the halogens-Group7. Each halogen…