What is the balanced equation for the copper oxide formation?

When the unbalanced equation of the formation of CuO is:

Cu  +  O2 → CuO

now the number of O atoms are not equal on both sides of the equation.

as O atoms on the left side 2 atoms and on the right side 1 atom. 

so we will put 2 CuO instead of CuO 

now the number of O atoms on both sides are equal 2

but now the number of Cu atoms are not equal on both sides so, we put 2 Cu instead of Cu.

∴ the final balanced equation of CuO formation is:

2Cu +  O2 → 2CuO

Density and pressure