Molecular Polarity: Chemistry

Describe and classify multiple chemistry terms correctly

What is electronegativity?

An atom’s ability to attract shared electrons in a chemical bond.

What makes a bond polar?

Two bonded atoms have different electronegativities, so electrons are shared unequally. The more electronegative atom becomes slightly negative, and the other becomes slightly positive.

What is a polar molecule?

A molecule with an uneven distribution of charge overall because its bond dipoles do not cancel.

What determines whether a molecule is polar or nonpolar?

Both bond polarity and molecular shape. The shape determines whether the bond dipoles cancel.

Why is CO₂ nonpolar but H₂O polar?

• CO₂: Linear and symmetrical. Its two polar C=O bonds pull in opposite directions and cancel.

• H₂O: Bent. Its O–H bond dipoles do not cancel, so the molecule is polar

Can a molecule have polar bonds but be nonpolar overall?

Yes. If its symmetrical shape causes the bond dipoles to cancel, like CO₂ or CCl₄ …Remember: Polar bonds do not automatically mean a polar molecule!

What are intermolecular forces?

Attractions between separate molecules. They help determine melting point, boiling point, and other physical properties.

What are London dispersion forces (LDFs)?

Attractions caused by temporary changes in electron distribution. They occur in all atoms and molecules, including nonpolar molecules.

What are dipole-dipole forces?

Attractions between the positive end of one polar molecule and the negative end of another polar molecule.

What is hydrogen bonding?

A particularly strong type of attraction between molecules when hydrogen is bonded directly to N, O, or F, and is attracted to N, O, or F on a neighboring molecule.

How do you identify which IMFs a substance has?

• All molecules: London dispersion forces.

• Polar molecules: also dipole–dipole forces.

• Molecules with H directly bonded to N, O, or F: also hydrogen bonding.

How do you compare IMF strength?

Intermolecular force (IMF) strength depends on molecular size, shape, and surface area in addition to the type of interaction.

How do stronger intermolecular forces affect boiling point?

Stronger attractions require more energy to overcome, so the boiling point is generally higher.

How do intermolecular forces affect evaporation?

Stronger forces make it harder for molecules to escape into the gas phase, so evaporation is generally slower.

Why does water have a relatively high boiling point?

Water molecules form hydrogen bonds, which require extra energy to overcome.

How do stronger forces affect melting point?

Stronger attractions often lead to higher melting points, although molecular shape and how particles pack in a solid also matter.

What is overcome when a molecular substance boils?

The intermolecular forces between molecules are overcome, not the covalent bonds within each molecule.

Why do molecular compounds generally have lower melting and boiling points than ionic compounds?

Molecular compounds usually have attractions between separate molecules, while ionic compounds have strong electrostatic attractions between oppositely charged ions

What holds an ionic compound together?

Strong electrostatic attractions between oppositely charged ions in a crystal lattice.

Why do ionic compounds usually have high melting points?

A large amount of energy is needed to overcome the strong attractions between their ions.

Why are ionic solids brittle?

When their layers shift, ions with the same charge can line up beside one another. They repel, causing the crystal to crack

Why do ionic compounds conduct electricity when molten or dissolved, but not when solid?

Molten and dissolved ionic compounds have mobile ions that carry charge. In a solid, the ions are fixed in place.

What are typical properties of molecular compounds?

They generally have lower melting and boiling points than ionic compounds and usually do not conduct electricity because they lack freely moving charged particles.

Why do some molecular substances dissolve in water while others do not?

Water is polar, so it generally dissolves polar substances better than nonpolar ones. Dissolving depends on whether the new attractions between solute and solvent particles are favourable compared with the attractions already present.

How do you explain a compound's properties using its forces?

Identify the particles, identify the attractions between them, and explain how those attractions affect the property.

Example: NaCl has strong attractions between ions, giving it a high melting point. Solid NaCl cannot conduct electricity because its ions cannot move freely.