How do you write "calcium + nitrogen -> calcium nitride"?
Calcium is a metal, so its formula will simply be
Nitrogen is a diatomic molecular compound, making it
Since calcium nitride is an ionic compound, by evaluating its constituent ions we can determine its formula. The calcium ion is a 2+ ion, or
Balancing the equation, then, you will notice that the number of nitrogens on each side balances However, on the left side of the equation we have
I have also provided the states of each reactant and the product at room temperature, though without further information on reaction conditions these cannot be confirmed as correct and so I recommend leaving them out unless there is further advice given.
It may seem unnatural to refer to these species as "calciums" and the like, but it is important to be aware that we are not always talking in terms of atoms: in this case, we may also be referring to the ions on the right hand side of the equation.