Write the formula for a complex formed between ni2 and nh3, with a coordination number of 5.

An atom's coordination number in a molecule refers to the number of atoms attached with the central atom. The coordination number in chemistry illustrates the number of neighbor atoms in regard to a central atom. The coordination number can differ from as low as two to as high as sixteen. The value of the coordination number relies upon the comparative sizes of the central atoms and the ligands and by the charge from the ion's electronic configuration.  

The NH₃ is a neutral ligand. Thus, the formula for a complex produced in between Ni²⁺ and NH₃ with a coordination number 5 will be [Ni(NH₃)₅]²⁺.

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.