( ( Because ( it ( ( takes ( two electrons ) ) ( to ( form ( a ( covalent bond ) ) ) ) ) ) ) ( , ( we ( ( can ( calculate ( ( the number ) ( of ( ( nonbonding ( electrons ( in ( the molecule ) ) ) ) ( by ( ( subtracting ( two electrons ) ) ( from ( ( the ( total number ) ) ( of ( ( valence electrons ) ( for ( ( each bond ) ( in ( the ( skeleton structure ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Because) (S (NP (PRP it)) (VP (VBZ takes) (NP (CD two) (NNS electrons)) (S (VP (TO to) (VP (VB form) (NP (DT a) (JJ covalent) (NN bond)))))))) (, ,) (NP (PRP we)) (VP (MD can) (VP (VB calculate) (NP (NP (DT the) (NN number)) (PP (IN of) (S (VP (VBG nonbonding) (NP (NP (NNS electrons)) (PP (IN in) (NP (DT the) (NN molecule)))) (PP (IN by) (S (VP (VBG subtracting) (NP (CD two) (NNS electrons)) (PP (IN from) (NP (NP (DT the) (JJ total) (NN number)) (PP (IN of) (NP (NP (JJ valence) (NNS electrons)) (PP (IN for) (NP (NP (DT each) (NN bond)) (PP (IN in) (NP (DT the) (NN skeleton) (NN structure)))))))))))))))))) (. .)))
Because it takes two electrons to form a covalent bond, we can calculate the number of nonbonding electrons in the molecule by subtracting two electrons from the total number of valence electrons for each bond in the skeleton structure.
(ROOT (S (NP (NNP Valence)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (JJ covalent) (NNS bonds))))) (SBAR (S (NP (DT an) (NN atom)) (VP (MD can) (VP (VB form))))))) (. .)))
Valence is the term for the number of covalent bonds an atom can form.