Q15. Classify the molecules as polar or nonpolar.

Background

Topic: Molecular Polarity

This question tests your understanding of how to determine whether a molecule is polar or nonpolar based on its Lewis structure, molecular geometry, and the electronegativity of its atoms.

Key Terms and Concepts:

• Polarity: A molecule is polar if it has a net dipole moment due to uneven distribution of electrons (as a result of differences in electronegativity and molecular shape).

• Nonpolar: A molecule is nonpolar if the electron distribution is symmetrical and there is no net dipole moment.

• Lewis Structure: Shows the arrangement of atoms and lone pairs in a molecule.

• Molecular Geometry: The 3D arrangement of atoms in a molecule, which affects polarity.

Step-by-Step Guidance

1. Examine the Lewis structure of each molecule. Identify the central atom and the surrounding atoms or groups.

2. Determine the molecular geometry (shape) for each molecule using VSEPR theory. For example, is it trigonal pyramidal, tetrahedral, linear, etc.?

3. Assess the electronegativity differences between the central atom and the surrounding atoms. Are the bonds polar?

4. Consider the symmetry of the molecule. If the polar bonds are arranged symmetrically, the dipoles may cancel, resulting in a nonpolar molecule. If not, the molecule is polar.

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Q16. Amino acids differ from each other by their unique branching “R” groups. Study the branching “R” group of the amino acid serine and choose the single most important type of intermolecular force that the side chain of serine experiences with water.

Background

Topic: Intermolecular Forces

This question is about identifying the strongest type of intermolecular force between the side chain of serine (which contains an -OH group) and water molecules.

Key Terms and Concepts:

• Intermolecular Forces: Forces of attraction between molecules, including dispersion forces, dipole-dipole interactions, hydrogen bonds, and ionic bonds.

• Hydrogen Bond: A strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (N, O, or F).

• Serine Side Chain: Contains an -OH group, which can participate in hydrogen bonding with water.

Step-by-Step Guidance

1. Identify the functional group present in the side chain of serine (look for -OH, -NH2, etc.).

2. Recall which intermolecular forces are possible for molecules containing -OH groups (hydrogen bonding is especially important here).

3. Compare the strength of hydrogen bonds to other intermolecular forces (dispersion, dipole-dipole, ionic) in the context of serine and water.

4. Decide which force is the most significant for the interaction between the serine side chain and water.

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