原子数，原子价，化合价。

The number of atoms in a molecule.

(化学)有五个原子价的。

(Chemistry) having a valence of five.

钾在化合物中的原子价是1。

Potassium in compounds has valence 1.

加上钪和钇，一起组成稀土金属。它们的原子都有相似的配置，以及相似的物理和化学行为，最常见的原子价是3和4。

With scandium and yttrium they make up the rare earth metals. their atoms have similar configurations and similar physical and chemical behaviour; the most common valences are3and4