= Bond pair
= Bonding pair
{synonym}
A <bond pair> is an <electron pair> allocated to a connection between two <chemical atoms> in a <Lewis structure>. A single line stands for one <bond pair>, or two <electrons>. A double connection contains two <bond pairs>, or four <electrons>; a triple connection contains three <bond pairs>, or six <electrons>. A <bond pair> is shared bookkeeping for the combined arrangement, rather than two distinguishable <electrons> each permanently owned by one endpoint.
In <water>, two <bond pairs> use $2\times2=4$ of the eight <valence electrons>. In <Ammonia>, three <bond pairs> use $3\times2=6$ of the eight <valence electrons>. In $\mathrm{O=C=O}$, each C=O connection contains two <bond pairs>, so there are four <bond pairs> in the entire <carbon dioxide> <molecule>. Counting connections and counting <bond pairs> therefore give different answers for multiple connections.
The same <bond pair> is treated differently for different questions: both endpoints count its two <electrons> for the <octet rule>, whereas each endpoint receives just one <electron> for <formal charge>. Neither convention asserts equal physical <electron density> at the endpoints. For electronic shapes, occupancy, and <energy>, see <molecular orbital theory> rather than treating a <bond pair> line as an entire <wavefunction>.
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