( ( ( A ( double bond ) ) ( between ( two atoms ) ) ) ( ( is ( ( ( formed ( by ( ( the sharing ) ( of ( ( ( ( ( ( two pairs ) ( of electrons ) ) , ) ( one ( in ( a ( sigma bond ) ) ) ) ) and ) ( one ( in ( a ( pi bond ) ) ) ) ) ) ) ) ) , ) ( with ( ( electron density ) ( concentrated ( on ( ( two ( opposite sides ) ) ( of ( the ( internuclear axis ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (JJ double) (NN bond)) (PP (IN between) (NP (CD two) (NNS atoms)))) (VP (VBZ is) (VP (VBN formed) (PP (IN by) (NP (NP (DT the) (NN sharing)) (PP (IN of) (NP (NP (NP (CD two) (NNS pairs)) (PP (IN of) (NP (NNS electrons)))) (, ,) (NP (NP (CD one)) (PP (IN in) (NP (DT a) (NN sigma) (NN bond)))) (CC and) (NP (NP (CD one)) (PP (IN in) (NP (DT a) (NN pi) (NN bond)))))))) (, ,) (PP (IN with) (NP (NP (NN electron) (NN density)) (VP (VBN concentrated) (PP (IN on) (NP (NP (CD two) (JJ opposite) (NNS sides)) (PP (IN of) (NP (DT the) (NN internuclear) (NNS axis)))))))))) (. .)))
A double bond between two atoms is formed by the sharing of two pairs of electrons, one in a sigma bond and one in a pi bond, with electron density concentrated on two opposite sides of the internuclear axis.
(ROOT (S (NP (DT A) (JJ double) (NN bond)) (VP (VBZ consists) (PP (IN of) (NP (NP (CD one) (NN sigma) (NN bond)) (CC and) (NP (CD one) (NN pi) (NN bond))))) (. .)))