why there is a negative charge on cyanide..
Because it has 13 protons and 14 electrons.
Are the three bonds between c and N in cyanide ion are all covalent??
Yes. As it is isoelectronic with N
2, it is perhaps more helpful to think of it as C
- and N, each sharing 3 electrons. The formal negative charge is on the C (imagine removing a proton from N
2).