In h2−, how many electrons occupy the mo shown?

Atomic number of H = 1

Valence electron configuration = 1s¹

When 2 H atoms combine, two 1s orbitals overlap resulting in the formation of a sigma bond.

H₂ Molecular configuration = σ1s²

In H₂⁻ there is an addition of 1 electron which goes to occupy the σ* antibonding orbital:

H₂⁻ = σ1s² σ*1s¹

Thus, 3 electrons will occupy the MO of H2⁻ in which:

2 electrons are bonding

1 electron antibonding

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.