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One chemical that is an exception to the octet rule is BCl3, or boron trichloride. Boron is a group 13 element, meaning it has 3 valence electrons. So each of these three valence electrons forms a single bond with a chlorine atom. This gives a total of 3*2=6 electrons surrounding boron, which is two less than the standard octet. As a result, BCl3 is a highly reactive compound and it acts as a Lewis acid, meaning that it readily accepts a pair of electrons from an electron donor to make an octet.
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