hep·tad /ˈhɛpˌtæd/
七個,七個成套之物,七價原子
Hep·tad n. Chem. An atom which has a valence of seven, and which can be theoretically combined with, substituted for, or replaced by, seven monad atoms or radicals; as, iodine is a heptad in iodic acid. Also used as an adjective.
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heptad
n : the cardinal number that is the sum of six and one [syn: seven,
7, VII, sevener, septet]