Question

Why do dipole-dipole interactions occur between molecules of \(\mathrm{CO}\) and molecules of NO? 1\. They both contain at least one electronegative element. 2\. They both have dipole moments. 3\. One is more polar than the other. 4\. They both contain oxygen.

Short answer

Dipole-dipole interactions occur between CO and NO molecules because they both contain at least one electronegative element and have dipole moments, leading to the formation of polar bonds. The electronegativity difference between the atoms in these molecules and their molecular shape allows for dipoles to form and interact with each other.

Step-by-step solution

Examine the Electronegativity of Elements

The electronegativity difference between atoms plays a key role in determining the polarity of a molecule. Carbon monoxide (CO) has a polar bond due to the electronegativity difference between carbon and oxygen. Nitrogen monoxide (NO) has a polar bond due to the electronegativity difference between nitrogen and oxygen.

Determine the Dipole Moments

In addition to the electronegativity difference, the presence of a dipole moment demonstrates that a molecule has dipole-dipole interactions. CO and NO molecules both have dipole moments as the electrons are not shared equally between the atoms and the molecular shape allows for a dipole to form.

Compare Polarities

The polarity of a molecule can impact the strength of dipole-dipole interactions, but having different polarities does not prevent interactions from occurring. Comparing the polarities of CO and NO is not necessary to explain why dipole-dipole interactions occur between these two molecules.

Check for Oxygen Presence

Both CO and NO molecules contain oxygen, but the presence of oxygen alone is not enough to explain the occurrence of dipole-dipole interactions. The key factors are the polarity of the bonds and the presence of dipole moments in both molecules. Based on this analysis, the best answer is: 1. They both contain at least one electronegative element. 2. They both have dipole moments.

Key concepts

Electronegativity

Electronegativity is a fundamental chemical concept, referring to the ability of an atom to attract shared electrons in a chemical bond.

Imagine atoms in a molecule as players in a tug-of-war game. Electronegativity then is akin to the strength of each player. Elements such as fluorine, oxygen, and nitrogen are like the strongest players, exerting greater pull on the electrons. When these atoms are in a bond with less electronegative atoms, like hydrogen or carbon, they tend to 'win' the electron tug-of-war, creating a polarized bond where electrons are not shared equally.

This imbalance in electron distribution can lead to an asymmetrical electron cloud around the molecule, setting the stage for various intermolecular interactions, including dipole-dipole interactions.

Polarity of Molecules

While electronegativity tells us about the pull of individual atoms, the polarity of molecules is all about the team dynamics—how these atoms come together to form a molecule. A molecule is polar when there is a significant difference in electronegativities among its atoms, leading to a separation of charge.

Think of it like a schoolyard pick, with atoms selecting bonding partners. Some pairs will be more balanced in their electron-sharing (nonpolar), while others are mismatched, leading to one atom hoarding more electrons (polar).

Understanding Molecular Geometry

The shape of a molecule also plays a significant role in its polarity. Even if a molecule has polar bonds, if the shape is symmetrical, the polarities cancel out, and the molecule is nonpolar. So, both the arrangement of atoms and the type of atoms are crucial for molecule polarity.

Dipole Moments

Dipole moments are like arrows pointing from the positively charged end of a molecule to the negatively charged end. They are a vector quantity, which means they have both magnitude and direction, determined by the difference in electronegativity and the distance between the charged ends.

In the dance of molecules, the dipole moment is the choreography showing the imbalance in the electron dance. Larger differences in electronegativity and longer distances result in stronger dipole moments.

Intermolecular Attractions

Dipole moments are the reason why some molecules are attracted to each other. They line up so that the positive end of one molecule is near the negative end of another, creating an intermolecular dance that holds substances together and significantly affects properties like boiling points and solubility. In the case of CO and NO, their dipole moments invite them into this dance of attraction, leading to dipole-dipole interactions.