Which molecule would you predict would be more stable: be2− 2 or be2?

   
 C2^2+ will or will not exist? 
 Because of sp mixing Ď3> Ď€1; assume Ď*2 antibonding that is not always the case (can be approximately nonbonding): 
 C2^2+ = 6e- Ď1(2e-) Ď*2 (2e-) Ď€1(2e-) Ď3(0e-) Ď€2*(0e-) Ď4(0e-) * 
 Bond Order (bo) = [ÎŁ (bonding e-) - ÎŁ (antibonding e-)]/2 
 = [4 (Ď1(2e-)Ď€1(2e-)) -2 (Ď*2 (2e-))] = 1 
 So it is bonding and predicted to exist. 
 b. Li2 will or will not exist? 
 (cf H2!) Li2 = 2e Ď1(2e-) Ď*2 (0e-) bo = 1; should (and does) exist 
 c. Be2^2+ will or will not exist? 
 Be2^2+ = 2e Ď1(2e-) Ď*2 (0e-) bo = 1; should exist 
 d. Li2^2- will or will not exist? 
 Li2^2- 4e- Ď1(2e-) Ď*2 (2e-) bo = 0; will not exist