( ( A ( lithium atom ) ) ( ( has ( ( ( a ( ( still heavier ) nucleus ) ) and ) ( three electrons ) ) ) . ) )
(ROOT (S (NP (DT A) (NN lithium) (NN atom)) (VP (VBZ has) (NP (NP (DT a) (ADJP (RB still) (JJR heavier)) (NN nucleus)) (CC and) (NP (CD three) (NNS electrons)))) (. .)))
A lithium atom has a still heavier nucleus and three electrons.
(ROOT (S (NP (NNP Lithium)) (VP (VBZ has) (NP (CD three) (NNS electrons))) (. .)))