A substance that is made up of molecules, each of which
contains two iodine atoms is called an element.
A species of atoms having the atomic number and the same
number of protons in their atomic nuclei (i.e. the same atomic number, or Z).
is called a chemical element or simply element. 118 elements were already
identified, and the first 94 of them occur on Earth naturally, while the
remaining 24 are synthetic elements. Even with chemical means, elements cannot
be broken down into simpler substance. The most common element in the Earth’s
crust that is known to mankind is oxygen.
