Question

The molar mass of I_2 is 254gmol, and that of astatine (At2) is 420gmol. Which one has the higher melting point and why?

A. I_2, because it has less molar mass, and, therefore, the dispersion forces between molecules are smaller.
B. I_2, because it has the higher molar mass, and, therefore, the dispersion forces between molecules are higher.
C. At2, because it has higher molar mass, and, therefore, stronger dispersion forces.
D. At2, because it has less molar mass, and, therefore, stronger dispersion forces.

Answer 1

At2 has a higher melting point than I2 because its higher molar mass leads to stronger London dispersion forces, which increases the energy required to overcome these intermolecular forces.

Step-by-step explanation:

When comparing the melting points of I2 and At2, we should consider intermolecular forces, particularly London dispersion forces, which are pivotal in determining these physical properties.

The melting point of a substance will typically increase with stronger intermolecular forces. In this case, since At2 has a higher molar mass than I2, it is expected to exhibit stronger dispersion forces.

The correct answer to the question is: C. At2, because it has higher molar mass, and, therefore, stronger dispersion forces.

This occurs because larger and heavier molecules have more electrons that can contribute to temporary dipoles causing stronger intermolecular attraction. Hence, a substance like At2 will have a higher melting point compared to I2 due to these increased dispersion forces.