Late in the nineteenth century, Werner conceived of a variable coordination number for some atoms to explain the properties of complex inorganic molecules.
He suggested that bonding in organic compounds was only an extension of his concept rather than some different phenomenon.
In Werner’s terminology, valence indicates the number of bonds that an atom can form.
Coordination number refers to the number of groups connected to a given atom.
Since many compounds contain multiple bonds between atoms, valence and coordination number are not necessarily the same.