Question

Which of the following elements has the highest melting point?
A) ${\text{Ba}}$
B) ${\text{Sr}}$
C) ${\text{Ca}}$
D) ${\text{Be}}$

Answer 1

We are given four elements barium $\left( {{\text{Ba}}} \right)$, strontium $\left( {{\text{Sr}}} \right)$, calcium $\left( {{\text{Ca}}} \right)$ and beryllium $\left( {{\text{Be}}} \right)$. All the four elements belong to group 2 of the periodic table. To solve this we must know the trend in melting point of the group 2 of the periodic table. The melting point depends on the atomic size.

Complete solution: We know that the temperature at which the solid and liquid forms of a pure substance exist in an equilibrium is known as melting point. In simple words, the temperature at which a solid is converted to liquid is known as melting point.
To convert the solid to liquid, the bonds between the atoms of solid are broken. To break these bonds energy is supplied to the solid in the form of heat.
We are given four elements barium $\left( {{\text{Ba}}} \right)$, strontium $\left( {{\text{Sr}}} \right)$, calcium $\left( {{\text{Ca}}} \right)$ and beryllium $\left( {{\text{Be}}} \right)$. All the four elements belong to group 2 of the periodic table.
The atomic numbers of the given elements in the group 2 of the periodic table are as follows:
Beryllium $\left( {{\text{Be}}} \right)$-4
Calcium $\left( {{\text{Ca}}} \right)$-20
Strontium $\left( {{\text{Sr}}} \right)$-38
Barium $\left( {{\text{Ba}}} \right)$-56
We know that as the atomic number increases the size of the atom increases. As the atomic size increases the bonds between the atoms become weaker.
As the bonds become weaker less amount of energy is required to break these bonds. This results in the lowest melting point.
Thus, the bond strength in beryllium $\left( {{\text{Be}}} \right)$ will be the highest.
Thus, the element having the highest melting point is ${\text{Be}}$.

Therefore, the correct answer is (D).

Note: We can also solve this by using the trend in melting point of the group 2 elements in the periodic table. The trend in melting point for group 2 is that as we go down the group from top to bottom, the melting point decreases. The elements are arranged in the order beryllium $\left( {{\text{Be}}} \right)$-4, calcium $\left( {{\text{Ca}}} \right)$-20, strontium $\left( {{\text{Sr}}} \right)$-38, barium $\left( {{\text{Ba}}} \right)$-56. Thus, the element having the highest melting point is ${\text{Be}}$.