Consider two ionic compounds containing the same anion but different cations: Compound 1 has a melting point of 801 °C, and Compound 2 has a melting point of 770 °C. Which of the following choices best predicts the likely identities of the cations in these compounds and explains the physical reason for their difference in melting point? Ion 1 Ion 2 Reasoning A) K+ Na+ Potassium is larger than sodium, so the London Dispersion Forces (LDFs) in Compound 1 are stronger than they are in Compound 2. This means that more energy is required to break
Consider two ionic compounds containing the same anion but different cations: Compound 1
has a melting point of 801 °C, and Compound 2 has a melting point of 770 °C. Which of the
following choices best predicts the likely identities of the cations in these compounds and
explains the physical reason for their difference in melting point?
Ion 1 Ion 2 Reasoning
A) K+ Na+
Potassium is larger than sodium, so the London Dispersion Forces (LDFs)
in Compound 1 are stronger than they are in Compound 2. This means
that more energy is required to break the LDFs, resulting in a higher
melting point.
B) K+ Na+
Potassium is more massive than sodium, so the gravitational forces
holding Compound 1 together are stronger than in Compound 2. Thus,
more energy is required to break the gravitational forces, resulting in a
higher melting point.
C) Na+ K+
Sodium is more electronegative than potassium, so the dipole-dipole forces
in Compound 1 are stronger than they are in Compound 2. This means
that more energy is required to break the dipole-dipole forces, resulting in
a higher melting point.
D) Na+ K+
Sodium is more electronegative than potassium, so the covalent bonds in
Compound 1 are more polar than they are in Compound 2. This means
that more energy is required to break the covalent bonds, resulting in a
higher melting point.
E) Na+ K+
Sodium has a smaller ionic radius than potassium, so the electrostatic
attraction between the ions in Compound 1 is stronger than it is in
Compound 2. Thus, more energy is needed to break the ionic bonds,
resulting in a higher melting point.
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