There are three different types of bond: ionic, covalent (including coordinate) and metallic bonding. The basic cause of bonding is the same in each case, this is that the positively charged nuclei and negatively charged electrons are arranged in a way that the electrostatic attractons outweigh the repulsions.
- A covalent bond has a pair of electrons with opposed spins shared between two atoms with each atom giving one electron.
Each atom gives one electron to form a bond pair in which the electron spins are opposed.
- A coordinate bond is a covalent bond in which both electrons come from one of the atoms
This is the same as a covalent bond except that both electrons which form the bond pair come from the same atom
- A ionic bond is a bond formed by the electrical attraction between the positive and negative ions (cations and anions)
One atom gives one or more electrons to the other and the resulting cation (+) and anion (-) attract one another electrically. It normally forms a lattice in which each cation is surrounded by several.
Attractive and repulsive forces
All bonding results from electrical attractions and repulsions between the protons and electrons, with attractions outweighing repulsions.
In covalent bonds the electrons in the pair between the atoms repel one another but this is overcome by their attractions to both nuclei. If atoms get too close together the nuclei and the inner electrons will repel those of the other atom so the bond has a certain length. Also the electron spins must be opposite for the bonds to form.
In ionic bonding cations and anions are arranged so that each cation is surrounded by several anions and vice versa to maximise attraction and minimise repulsion. Again repulsions from inner elcetrons and nuclei prevent the ions from getting too close together.
This important bond type is discussed in Solid structures, it essentially consists of a lattice of positive ions held together by a 'sea' of delocalised electrons given up by each atom.
Electronegativity and bond polarity
In a covalent bond the electron pair isn't usually shared exactly evenly between the two atoms unless they're the same. Therefore one atom takes up a slightly negative charge and the other slightly positive, the bond is now said to be polar. These small charges are written over atoms using the symbols δ+ and δ-. Coordinate bonds are always polar, since the atom giving both electrons to the bond cannot completely lose its right over one electron.
- Electronegativity is a…