n. 七个, 成七的一组, 七价原子

[化] 七价物; 七价的

[医] 七价元素

[ noun ]
the cardinal number that is the sum of six and one
<noun.quantity>

Heptad \Hep"tad\, n. [L. heptas the number seven. Gr. ?, ?, fr.
"epta` seven.] (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.