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Chapter 11: Problem 7

The compounds \(\mathrm{Br}_{2}\) and ICl have the same number of electrons, yet \(\mathrm{Br}_{2}\) melts at \(-7.2^{\circ} \mathrm{C}\) and ICl melts at \(27.2^{\circ} \mathrm{C} .\) Explain.

Short Answer

Expert verified
ICl has a higher melting point than Br2 even though both have the same number of electrons because ICl has stronger intermolecular dipole-dipole forces due to the difference in electronegativity between iodine and chlorine atoms, whereas Br2 has comparatively weaker London dispersion forces as it's a nonpolar molecule consisting of identical bromine atoms.

Step by step solution

01

Understanding the types of bonds

Firstly, it's important to understand the type of bonds in both molecules. The compound Br2 is a diatomic molecule consisting of two bromine atoms joined by a covalent bond, while ICl is a heteronuclear diatomic molecule, which is formed by a covalent bond between iodine and chlorine atoms. Covalent bonds involve the sharing of electrons between atoms.
02

Identifying intermolecular forces

We then move to the identification of the type of intermolecular forces in both compounds. In a molecule of Br2, the atoms are identical, so there is no difference in electronegativity, and the molecule is nonpolar. Hence, the intermolecular force acting between Br2 molecules is London dispersion forces (LDF). On the other hand, ICl molecule has atoms with different electronegativities, which makes the molecule polar. Consequently, its intermolecular forces are dipole-dipole forces (along with LDF).
03

Explaining the difference in melting points

Now we can explain the difference in melting points using the information about intermolecular forces. The dipole-dipole forces in ICl are stronger than the London dispersion forces in Br2. So, it requires more energy (or a higher temperature) to break the intermolecular forces in ICl than in Br2. That's the reason ICl has a higher melting point than Br2, despite both having the same number of electrons.

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