What hybrid orbitals are used by the Nitrogen atoms in H2N-NH2?
The molecule H2N-NH2, also known as hydrazine, each Nitrogen atom has 3 bond pairs (two N-H and one N-N bonds) and one lone pair. So, the steric number of each Nitrogen atom is,
steric number=number of bond pairs + number of lone pairs
steric number=3 + 1 = 4
The number 4 correlates to sp3 hybridization. Also, by looking at hydrazine’s structure, it’s obvious that lone pairs are not next to a pie bond, so the steric number will contribute to the actual state of hybridization and not fall within any exception.
(Read the hybridization concept from the chapter Covalent Bond, part of the Introductory Organic Chemistry course, for the detailed explanation, examples, calculating steric numbers and exceptions.)
The orbital diagram gives a clearer picture of hybridization.
Each nitrogen atom in H2N-NH2 has five valence electrons distributed in s and p-orbitals. Each Nitrogen atom's s and p orbitals mix to form sp3 hybrid orbitals. Note that the lone pair is also part of the sp3 hybrid orbitals.
The hybrid orbitals are oriented in trigonal pyramidal shape around the central atom of Nitrogen to minimize inter-electronic repulsions.
The s-orbitals of Hydrogen overlap to form the N-H (sp3-s) bond, and the sp3 orbitals of two Nitrogen overlap to form the N-N (sp3-sp3) bond forming hydrazine NH2-NH2 molecule. The lone pairs are oriented away to avoid interelectronic repulsions.
(More tutorials on sp3, sp2, and sp hybridization are covered in the Introductory Organic Chemistry course.)