Why don’t you have friends?
Answer:
The atomic numbers of both are 54 while the mass numbers are 131 and 133 respectively.
Explanation:
- The number of protons = Atomic number. So, if the atom has 54 protons and it remained unchanged, then the two types of atoms of this element both have atomic numbers of 54.
- On the other hand, mass number is the sum of protons and neutrons
So, if type 1 has protons = 54 and neutrons = 77: mass number = 54 + 77 = 131
if Type 2 has protons = 54 and neutrons = 79: mass number = 54 + 77 = 133
(Since the possibility of atoms of the same element to have different mass numbers but the same atomic number is called isotopy). The two types of atoms with mass numbers 131 and 133 described are isotopes.
Iodine is one of seven elements that usually form as diatomic molecules. These other "diatomics" are

and

. They typically bond to themselves.
Iodine has seven valence electrons. Using valence shell electron pair repulsion (VSEPR) theory, we can predict the Lewis dot structure for

. We see there are fourteen electrons, and we can make a covalent bond, leaving three lone pairs on each atom. The bond replaces two electrons, so the number of electrons shared is two.