How To Calculate Coordination Number?

Short tutorial on what is coordination number and how to calculate coordination number with a neat example.

Calculate Coordination Number of an Element

In coordination chemistry, the coordination number is the number of donor atoms attached to the central ion. Coordination numbers are normally between 2 and 9. The number of bonds depends on the size, charge, and electron configuration of the metal ion and the donor atoms.

The maximum coordination number for a metal is related to the electronic configuration of the metal ion and to the ratio of the size of the donor atoms and the metal ion. Large metals and small donor atoms lead to high coordination numbers. Small metals with large donor atoms lead to low coordination numbers.
Let us learn here how to calculate coordination number of an element with a simple example.
Steps on How to Calculate Coordination Number?
Step 1: Identify the central atom in the chemical formula.
Step 2: Locate the atom, molecule, or ion nearest the central metal atom.
Step 3: Add the number of atoms of the nearest atom/molecule/ions. The central atom may only be bonded to one other element. If the central atom is in the middle of the formula, you will need to add up the atoms in the entire molecule.
Step 4: Find the total number of nearest atoms. If the metal has two bonded atoms, add both numbers together.
Coordination Numbers Examples:

Example 1: Consider a methane molecule whose chemical formula is CH4. The central carbon atom is bonded to four hydrogen atoms, so its coordination number is 4.
Example 2: Consider ethylene molecule whose formula is H2C=CH2, the coordination number of each carbon is 3, where each C is bonded to 2H + 1C for a total of 3 atoms.

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