How would you calculate the formal charge of each atom in the following compounds: #NO#, #AlH_4^-# ?

Question

How would you calculate the formal charge of each atom in the following compounds:  #NO#, #AlH_4^-# ?

Avery Adams · Accepted Answer

How do you calculate the charge? Sum up the electrons, and sum up the nuclear charges, and the charge is the difference.

For #"tetrahydroaluminate anion"#, we know that there is a negative charge on the ion. The charge is formally centred on the aluminum nucleus, because it is associated with 4 bonding electrons rather than 3. Another way to look at the aluminate ion is as the alkali metal hydride adduct of #AlH_3#, i.e. #LiH*AlH_3#. Lithium aluminum hydride can still potentially deliver up to 4 equiv of hydride. For #NO#, this has a problematic Lewis representation with an odd electron. #N=O# is reasonable. We have #5+6# valence electrons to distribute. Around oxygen there are 2 lone pairs; around nitrogen there is one lone pair, and one single electron. Each centre is thus neutral.

Cooper Adams · Answer

undefined For NO: Nitrogen has a formal charge of 0, and oxygen has a formal charge of -1.

For AlH₄⁻: Aluminum has a formal charge of +1, and each hydrogen has a formal charge of 0.