Write the electronic configuration of two elements X and Y whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element X reacts with element Y. Draw electron-dot structure of the product and also state the nature of the bond formed between both the elements.

1. Electronic Configuration:

• Element $X$ (Atomic number = $20$): $2, 8, 8, 2$ (Calcium, a metal)
• Element $Y$ (Atomic number = $17$): $2, 8, 7$ (Chlorine, a non-metal)

1. Molecular Formula:

Element $X$ has $2$ valence electrons and needs to lose $2$ electrons to achieve a stable octet, forming $X^{2+}$. Element $Y$ has $7$ valence electrons and needs to gain $1$ electron to achieve a stable octet, forming $Y^-$.

To balance the charges, one atom of $X$ transfers its $2$ valence electrons to two atoms of $Y$ (each taking $1$ electron).

Therefore, the molecular formula of the compound is $XY_2$.

1. Nature of Bond:

The bond formed between element $X$ and element $Y$ is an ionic bond (or electrovalent bond), because it is formed by the complete transfer of electrons from a metal ($X$) to a non-metal ($Y$).

1. Electron-Dot Structure:

Chemical representation of electron transfer:

$$X^{\bullet}_{\bullet} + 2 \cdot \ddot{Y}: \rightarrow [X]^{2+} 2\left[ :\ddot{Y}: \right]^{-}$$