How to Identify the Intermolecular Force a Compound Has: London Dispersion, Dipole Dipole, H-Bonding

Summary

This video explains how to identify the type of intermolecular forces (IMFs) present in different substances. It distinguishes intermolecular forces from intramolecular bonds and outlines the three main IMFs: London dispersion, dipole–dipole interactions, and hydrogen bonding. The presenter demonstrates how to determine polarity using Lewis structures and a simple checklist, then applies these rules to various molecular examples. By the end, viewers learn how molecular structure and polarity dictate which IMFs a substance exhibits, along with tips and patterns to quickly recognize them in chemistry problems.

Takeaways

• 😀 Intermolecular forces (IMFs) are the attractions between molecules, distinct from intramolecular forces, which are the bonds within molecules.
• 😀 The three main types of intermolecular forces are London dispersion forces, dipole-dipole interactions, and hydrogen bonding.
• 😀 Nonpolar molecules only experience London dispersion forces.
• 😀 Polar molecules have both London dispersion forces and dipole-dipole interactions.
• 😀 Molecules with hydrogen directly bonded to fluorine, oxygen, or nitrogen (HF, HO, or HN) will experience all three types of IMFs: London dispersion, dipole-dipole, and hydrogen bonding.
• 😀 Carbon dioxide (CO2) is nonpolar, meaning it only has London dispersion forces.
• 😀 SF4 is polar because it has lone pairs on the central atom, which means it experiences London dispersion and dipole-dipole forces, but no hydrogen bonding.
• 😀 CH3NH2 has an NH bond, so it experiences London dispersion forces, dipole-dipole interactions, and hydrogen bonding.
• 😀 Any compound composed only of carbon and hydrogen (like C5H12) is nonpolar and will only experience London dispersion forces.
• 😀 Neon (Ne), being a single atom and nonpolar, also experiences only London dispersion forces.
• 😀 HCl is polar because chlorine is more electronegative than hydrogen, so it experiences London dispersion forces and dipole-dipole interactions, but not hydrogen bonding.

Q & A

What is the definition of intermolecular forces (IMFs)?

Intermolecular forces (IMFs) are the attractions between molecules. They differ from intramolecular forces, which are the bonds within a molecule, like covalent bonds between atoms.

What are the three main types of intermolecular forces?

The three main types of intermolecular forces are London dispersion forces, dipole-dipole interactions, and hydrogen bonding.

How do you determine which intermolecular forces a compound has?

You determine the intermolecular forces by first checking if the compound is polar or nonpolar. Nonpolar compounds only have London dispersion forces, while polar compounds also have dipole-dipole interactions. If a molecule has hydrogen attached to fluorine, oxygen, or nitrogen (HF, HO, or HN), it will also exhibit hydrogen bonding.

What is the rule for compounds that are nonpolar?

A compound is nonpolar if the central atom has no lone pairs and all surrounding atoms are identical. Nonpolar compounds only have London dispersion forces.

Why does carbon dioxide (CO2) only have London dispersion forces?

Carbon dioxide is nonpolar because its Lewis structure shows that the central carbon atom has no lone pairs and the two oxygen atoms are identical. Since it is nonpolar, it only has London dispersion forces.

What makes sulfur tetrafluoride (SF4) polar, and which intermolecular forces does it have?

Sulfur tetrafluoride is polar because the central sulfur atom has a lone pair, making the molecule asymmetrical. Therefore, it has London dispersion forces and dipole-dipole interactions but no hydrogen bonding.

What intermolecular forces are present in CH3NH2 (methylamine)?

Methylamine (CH3NH2) has all three intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonding. This is because it has an NH group, which is capable of hydrogen bonding.

What is a simple rule for determining if a compound with only carbon and hydrogen is nonpolar?

Any compound that consists solely of carbon and hydrogen atoms (like C5H12 or C4H10) is nonpolar and will only have London dispersion forces.

What type of intermolecular forces does neon (Ne) have?

Neon is a noble gas and consists of single atoms. It is nonpolar and has only London dispersion forces.

How can you determine if a compound has hydrogen bonding?

A compound has hydrogen bonding if it contains an H atom directly bonded to fluorine, oxygen, or nitrogen (HF, HO, or HN). This enables strong dipole-dipole interactions leading to hydrogen bonding.