six
An atom in a simple cubic lattice structure contacts six other atoms, so it has a coordination number of six. In a simple cubic lattice, the unit cell that repeats in all directions is a cube defined by the centers of eight atoms, as shown in Figure 4.

The coordination number is the number of ions that immediately surround an ion of the opposite charge within a crystal lattice. If you examine the figure below, you will see that there are six chloride ions immediately surrounding a single sodium ion.

For a simple cubic lattice, it is 6.

coordination number, also called Ligancy, the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours in a complex or coordination compound or in a crystal.

6
The simple cubic has a coordination number of 6 and contains 1 atom per unit cell.

For FCC and HCP systems, the coordination number is 12. For BCC it’s 8.

In NaCl crystal, each sodium ion is surrounded by 6 chloride ions and each chloride ion is surrounded by 6 sodium ions. So, the coordination number of NaCl as per definition will be 6:6.

The coordination number for the simple cubic structure is 6, whereas it is 8 and 12 for BCC and FCC respectively.

The coordination number of an atom in a molecule or polyatomic ion is found by counting the number of atoms bound to it (note: not by counting the number of chemical bonds).

CHEMISTRY GLOSSARY In a cubic close-packed (ccp) arrangement of atoms, the unit cell consists of four layers of atoms. The top and bottom layers (a) contain six atoms at the corners of a hexagon and one atom at the center of each hexagon. The atoms in the second layer (b) fit into depressions in the first layer.

In an fcc lattice the face centre atoms are the nearest atoms and one corner atom is surrounded by 4 faces in the x-plane, 4 faces in the y-plane and 4 faces in the z-plane. So, every corner atom is surrounded by (4 × 3) = 12 face centre atoms. Since they are the nearest they form the coordination number.

The number of other particles that each particle in a crystalline solid contacts is known as its coordination number. For a polonium atom in a simple cubic array, the coordination number is, therefore, six. Figure 3.

This arrangement of ions give the Na + ion as well as the Cl – ion a coordination number of 6. Each unit cell thus contains 4 Na + and 4 Cl -, with stoichiometry NaCl (Figure 7B). There are compounds where not all the octahedral holes are filled. In the case of cadmium chloride, CdCl 2 (Figure 8), the large chloride ions form a fcc framework.

In the case of polyatomic ions and molecules, the coordination number corresponding to a given atom can be calculated by counting the total number of atoms it is bonded to, be it a single bond or a double/triple bond.

The coordination number of a diamond is 4, as each carbon atom rests at the center of a regular tetrahedron formed by four carbon atoms. Here are the steps for identifying the coordination number of a coordination compound .