( ( Except ( at ( the ( 1s level ) ) ) ) ( , ( ( atoms ( with ( ( two electrons ) ( in ( their ( outer ( energy level ) ) ) ) ) ) ) ( ( are ( inclined ( to ( lose ( two electrons ) ) ) ) ) ; ) ) ) )
(ROOT (S (PP (IN Except) (PP (IN at) (NP (DT the) (JJ 1s) (NN level)))) (, ,) (NP (NP (NNS atoms)) (PP (IN with) (NP (NP (CD two) (NNS electrons)) (PP (IN in) (NP (PRP$ their) (JJ outer) (NN energy) (NN level)))))) (VP (VBP are) (ADJP (JJ inclined) (S (VP (TO to) (VP (VB lose) (NP (CD two) (NNS electrons))))))) (: ;)))
Except at the 1s level, atoms  with two electrons in their outer energy level are inclined to lose two electrons;
(ROOT (S (NP (NP (NNS Electrons)) (PP (IN in) (NP (NP (DT the) (JJ outer) (NN energy) (NN level)) (PP (IN of) (NP (DT an) (NN atom)))))) (VP (VBP are) (VP (VBN called) (NP (JJ valence) (NNS electrons)))) (. .)))