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How do nitrogen and hydrogen atoms bond to form a molecule of ammonia ( )?
A nitrogen atom has 7 electrons, and an electron configuration of . A hydrogen atom has only 1 electron, and an electron configuration of .
Nitrogen has 5 valence electrons meaning that 3 electrons are unpaired. Hydrogen has 1 valence electron and it is unpaired.
Each hydrogen atom needs one more electron to complete its valence energy shell. The nitrogen atom needs three more electrons to complete its valence energy shell. Therefore three pairs of electrons must be shared between the four atoms involved. The nitrogen atom will share three of its electrons so that each of the hydrogen atoms now have a complete valence shell. Each of the hydrogen atoms will share its electron with the nitrogen atom to complete its valence shell ( [link] ).
The above examples all show single covalent bonds , where only one pair of electrons is shared between the same two atoms . If two pairs of electrons are shared between the same two atoms, this is called a double bond . A triple bond is formed if three pairs of electrons are shared.
How do oxygen atoms bond covalently to form an oxygen molecule?
Each oxygen atom has 8 electrons, and their electron configuration is .
Each oxygen atom has 6 valence electrons, meaning that each atom has 2 unpaired electrons.
Each oxygen atom needs two more electrons to complete its valence energy shell. Therefore two pairs of electrons must be shared between the two oxygen atoms so that both valence shells are full. Notice that the two electron pairs are being shared between the same two atoms, and so we call this a double bond ( [link] ).
You will have noticed in the above examples that the number of electrons that are involved in bonding varies between atoms. We say that the valency of the atoms is different.
In the first example, the valency of both hydrogen and chlorine is one, therefore there is a single covalent bond between these two atoms. In the second example, nitrogen has a valency of three and hydrogen has a valency of one. This means that three hydrogen atoms will need to bond with a single nitrogen atom. There are three single covalent bonds in a molecule of ammonia. In the third example, the valency of oxygen is two. This means that each oxygen atom will form two bonds with another atom. Since there is only one other atom in a molecule of , a double covalent bond is formed between these two atoms.
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