( ( ( This ( shared pair ) ) ( of electrons ) ) ( ( is ( called ( a ( chemical bond ) ) ) ) . ) )
(ROOT (S (NP (NP (DT This) (VBN shared) (NN pair)) (PP (IN of) (NP (NNS electrons)))) (VP (VBZ is) (VP (VBN called) (NP (DT a) (JJ chemical) (NN bond)))) (. .)))
This shared pair of electrons is called a chemical bond .
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NNS electrons)) (VP (VBP are) (VP (VBN shared) (ADVP (RB equally)))))) (, ,) (NP (PRP it)) (VP (VBZ is) (VP (VBN called) (NP (NN nonpolar) (NNS bonds)))) (. .)))