Question

Identify the common property amongst beryllium, magnesium and calcium in the modern periodic table.

• A. Same number of electrons in the atom.
• B. Same number of electrons in the outermost shell.
• C. Same number of shells occupied by the electrons.
• D. Their atomic radii is the same.

Answer 1

The correct option is B Same number of electrons in the outermost shell.

The table given below is showing the distribution of electrons in the shells of the given elements:
$$\begin{array}{ccccc}\text{Elements}& \text{K-shell}& \text{L-shell}& \text{M-shell}& \text{N-shell}\\ \text{Beryllium}& \text{2}& \text{2}& \text{0}& \text{0}\\ \text{Magnesium}& \text{2}& \text{8}& \text{2}& \text{0}\\ \text{Calcium}& \text{2}& \text{8}& \text{8}& \text{2}\end{array}$$
As seen from the table, b​eryllium, magnesium and calcium have the same number of electrons (two) in the outermost shell. These three elements belong to the second group of the modern periodic table and are called alkaline earth metals. The atomic radii increase as we go down in a group. So, the given elements will not have the same atomic radii.