AS Chemistry: Bonding

A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei.In the formation of a simple covalent bond, each atom supplies one electron to the bond - but that doesn't have to be the case. A co-ordinate bond is a covalent bond in which both electrons came from the same atom.

Th reaction between ammonia and hydrogen chloride:If these colourless gases are allowed to mix, a thick white smoke of solid ammonium chloride is formed.

Co-ordinate bonding:A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei.In the formation of a simple covalent bond, each atom supplies one electron to the bond - but that doesn't have to be the case. A co-ordinate bond is a covalent bond in which both electrons come from the same atom.

The reaction between ammonia and hydrogen chloride:If these colourless gases are allowed to mix, a thick white smoke of solid ammonium chloride is formed.Ammonium ions, NH4+, are formed by the transfer of a hydrogen ion from the hydrogen chloride to the lone pair of electrons on the ammonia molecule.

When the ammonium ion is formed, the fourth hydrogen is attacked by a dative covalent bond, because only the hydrogen's nucleus is transferred from the chlorine to the nitrogen. The hydrogen's electron is left behind on the chlorine to form a negative chloride ion.One the ammonium ion has been formed, it is impossible to tell any difference between the dative covalent and ordinary covalent bonds. Although the electrons are show differently in the diagram, there is no difference in reality.

Representing co-ordinate bonds:In simple diagrams, a co-ordinate bond is shown by an arrow. The arrow points form the atom donating the lone pair to the atom accepting it.

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