Question

the melting and boiling points of some of the halogens are shown in the table. which of these options is the best prediction for the melting point and boiling point of bromine?

melting point = -7 °c and boiling point = 59 °c
melting point = 89 °c and boiling point = 59 °c
melting point = -7 °c and boiling point = 12 °c
melting point = 89 °c and boiling point = 12 °c

Explanation:

Identify the periodic trend

The halogens (Group 17) show a clear trend down the group.
As molecular mass increases, intermolecular forces strengthen.
Thus, melting and boiling points increase down the group.

Analyze the given data

For melting points:

• Chlorine (Period 3): \(-102\ ^\circ\text{C}\)
• Iodine (Period 5): \(114\ ^\circ\text{C}\)

Bromine (Period 4) must lie between these values:

$$-102\ ^\circ\text{C} < T_m < 114\ ^\circ\text{C}$$

For boiling points:

• Chlorine (Period 3): \(-34\ ^\circ\text{C}\)
• Iodine (Period 5): \(184\ ^\circ\text{C}\)

Bromine (Period 4) must lie between these values:

$$-34\ ^\circ\text{C} < T_b < 184\ ^\circ\text{C}$$

Evaluate the options

Let us test the given options:

• Option 1: \(T_m = -7\ ^\circ\text{C}\), \(T_b = 59\ ^\circ\text{C}\). Both values fit the ranges.
• Option 2: \(T_m = 89\ ^\circ\text{C}\), \(T_b = 59\ ^\circ\text{C}\). Here, \(T_m > T_b\), which is physically impossible.
• Option 3: \(T_m = -7\ ^\circ\text{C}\), \(T_b = 12\ ^\circ\text{C}\). Fits ranges, but bromine is liquid at room temperature.
• Option 4: \(T_m = 89\ ^\circ\text{C}\), \(T_b = 12\ ^\circ\text{C}\). Here, \(T_m > T_b\), which is physically impossible.

Confirm physical states

Bromine is well-known as a liquid at room temperature (\(25\ ^\circ\text{C}\)).
For a substance to be liquid at room temperature:

$$T_m < 25\ ^\circ\text{C} < T_b$$

This confirms \(T_m = -7\ ^\circ\text{C}\) and \(T_b = 59\ ^\circ\text{C}\) is correct.

Answer:

• (A) Melting point = -7 °C and boiling point = 59 °C (Correct answer)
• (B) Melting point = 89 °C and boiling point = 59 °C
• (C) Melting point = -7 °C and boiling point = 12 °C
• (D) Melting point = 89 °C and boiling point = 12 °C