MYP Chemistry Covalent Bonding and Compounds International College Spain

Covalent Bonds Covalent bonding is the bonding that occurs between non-metal atoms A covalent bond is formed when a pair of electrons is shared between two atoms A covalent bond is usually represented by a single line A lone pair is any electrons not shared in a covalent bond

Valence electrons These are the electrons in the outer energy shell of the atom Full electrons shells are stable electron arrangements Atoms share electrons to attain full outer shells

The hydrogen molecule Each hydrogen atom has only one outer (valence) electron HH

The hydrogen molecule The outer energy shell can overlap to make it appear as if there were two electrons in each shell HH

The hydrogen molecule Now there are two electrons (with negative charges) in between the two (positive) nuclei of the hydrogen atoms. This holds the nuclei, together forming a covalent bond HH

Covalent structure Covalent substances are usually simple molecules such as oxygen and hydrogen gas O 2 and H 2 OO An oxygen molecule

Covalent structures Soft structures (only weak forces holding the molecules together) Low melting and boiling points - they are often gases or liquids at RT, e.g. O 2, N 2 Non-conductors (no charged particles) Insoluble in water Soluble in other covalent liquids (e.g. petrol, tetrachloromethane)

Giant covalent structures If the covalent bonds keep linking atoms together in a never ending way this gives rise to giant covalent molecules Examples include the element carbon and silicon and the compounds silicon dioxide Such structures have billions of very strong bonds and high melting and boiling points.

Graphite

Diamond

Silicon dioxide

Covalent summary Shared electron pairs Full outer shells Molecules Non-conductors (exception graphite) Two types – simple and giant Simple covalent substances v. low mp Giant covalent substances v. high mp