Question

A species with a charge of -1 contains 57 electrons and 80 neutrons. What is the identity of the species. Note: The species shown may be hypothetical.

Answer 1

In a neutral atom, the number of protons is equal to the number of electrons.

Given that the charge on the ion of the element is -1. This means that there is one electron more than the number of protons in the element.

The atomic number = Number of protons = 57 -1 = 56

Element with atomic number 56 is Barium.

Mass number of the element = Number of protons + Number of neutrons

                                                = 56 + 80 = 136

So the identity of the species: $^{136}Ba^{-}$