Chemistry
State why water has two lone pairs of electrons in it's covalent molecule while ammonia has one lone pair.
Chemical Bonding
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Answer
Water contains two hydrogen atoms and one oxygen atom. The hydrogen atom [1] has one electron in it's valence shell while the oxygen atom [2,6] has 6 electrons in it's valence shell. Two hydrogen atom share one electron each and two unshared pairs of electrons are left as lone pairs as shown in the diagram below :
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In the case of ammonia, it contains three hydrogen atoms and one nitrogen atom. Nitrogen atom [2,5] has five valence electrons and hydrogen atom [1] has one valence electron. In ammonia, each of the three hydrogen atoms are bonded to the nitrogen atom by a pair of shared electrons. Thus, the nitrogen atom in ammonia is left with one lone pair of electrons as shown in the diagram below:
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