English Dictionary

francium

/ˈfɹansɪəm/

noun

The chemical element (symbol Fr) with an atomic number of 87. It is an intensely radioactive alkali metal that is not found in nature. / (countable) A single atom of this element.

Francium is a highly reactive alkali metal.

意味（1）

The chemical element (symbol Fr) with an atomic number of 87. It is an intensely radioactive alkali metal that is not found in nature.

The most elusive element of all, however, appears to be francium, which is so rare that it is thought that our entire planet may contain, at any given moment, fewer than twenty francium atoms.

意味（2）

(countable) A single atom of this element.

Notice that franciums are balanced without even thinking in moles, atoms, or whatever.