Question

If an ion ${\mathrm{E}}^{2+}$ contains $12$ neutrons and $10$ electrons, then what is the atomic number and mass num­ber of the element? Identify the element.

Answer 1

Given:

Number of neutrons$=12$

Number of electrons$=10$

Formula used:

1. Atomic number$=$number of electrons in an atom$=$number of protons in an atom
2. Mass number$=$Number of protons$+$Number of neutrons

Calculate the atomic number of the element:

The $+2$ charge on ${\mathrm{E}}^{2+}$ ion indicates that an ${\mathrm{E}}^{2+}$ ion is formed when atom $\mathrm{E}$ loses two electrons.

Thus,

Total electrons in the atom $\mathrm{E}$$=$Number of electrons lost by $\mathrm{E}$$+$Number of electrons in ${\mathrm{E}}^{2+}$

Total electrons in the atom $\mathrm{E}$$=2+10$

Total electrons in the atom $\mathrm{E}$$=12$

Atomic number$=$number of electrons in an atom$=12$

Thus, atomic number of the element is $12$.

Calculate the number of protons of the element:

Number of protons in an atom$=$Atomic number

Thus,

Number of protons in an atom$=12$

Calculate the mass number of the element:

Mass number$=$Number of protons$+$Number of neutrons

Mass number$=12+12$

Mass number$=24$

Thus, mass number of the element is $24$.

Identify the element:

The atomic number of the element is $12$.

Thus, the element is Magnesium $\mathbf{\left(}\mathbf{Mg}\mathbf{\right)}$.