The unit cell of nickel arsenide is shown here. (b) What is the empirical formula?

A unit cell is the smallest repeating unit in a crystal lattice that reflects the symmetry and structure of the entire crystal. It defines the arrangement of atoms, ions, or molecules in three-dimensional space. Understanding the dimensions and contents of the unit cell is crucial for determining the empirical formula of a compound, as it provides insight into the ratio of different types of atoms present.

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It is derived from the composition of the unit cell, indicating how many atoms of each element are present in the smallest repeating unit. For compounds like nickel arsenide, determining the empirical formula involves analyzing the number of nickel and arsenic atoms within the unit cell.

The coordination number is the number of nearest neighboring atoms surrounding a central atom in a crystal structure. It is essential for understanding the geometry and stability of the crystal lattice. In the case of nickel arsenide, knowing the coordination number helps in identifying how the nickel and arsenic atoms are arranged and how they interact within the unit cell, which is vital for calculating the empirical formula.