Chemical Polarity & IMF

What two factors determine a molecule’s polarity?

The difference in electronegativity between atoms and the asymmetry of the molecule’s structure

How does molecular polarity influence physical properties?

It affects surface tension, solubility, and melting/boiling points

What causes partial charges (δ+ and δ–) in a bond?

Unequal sharing of electrons between atoms with different electronegativities

Which elements are considered highly electronegative?

Fluorine (F), Oxygen (O), and Nitrogen (N)

If the electronegativity difference (ΔEN) is less than 0.4, what type of bond is formed?

Nonpolar covalent bond

If ΔEN is between 0.4 and 1.7, what type of bond is formed?

Polar covalent bond

If ΔEN is greater than 1.7, what type of bond is formed?

Ionic bond

What two factors determine whether a molecule as a whole is polar?

The polarity of its individual bonds and its molecular geometry (symmetry)

Why do polar molecules have a net dipole?

Because their bond dipoles do not cancel out due to asymmetrical arrangement

Why do polar molecules have higher boiling points than nonpolar molecules?

Stronger intermolecular forces (dipole-dipole or hydrogen bonding) require more energy to overcome

Why do polar molecules dissolve in water?

Because water is polar and interacts via dipole-dipole and hydrogen bonding (“like dissolves like”)

What structural feature makes a molecule nonpolar?

Either equal electron sharing or a symmetrical arrangement of polar bonds that cancel out dipoles

What are typical examples of nonpolar molecules?

Fats, oils, and waxes

Why do nonpolar molecules have lower boiling points?

They rely on weak London dispersion forces for intermolecular attraction

What are hybrid molecules in terms of polarity?

Molecules with both polar and nonpolar regions that can interact with both oil and water

What are surfactants, and why can they interact with both polar and nonpolar substances?

Surfactants have dual regions — a polar “head” and a nonpolar “tail” — allowing them to interact with both types of substances

What are Van der Waals forces?

Weak intermolecular forces that include dipole-dipole interactions and London dispersion forces

Between what types of molecules do dipole-dipole forces occur?

Between polar molecules

How do dipole-dipole forces align molecules?

The positive end of one molecule aligns with the negative end of another

What causes London dispersion forces (LDF)?

Temporary instantaneous dipoles caused by the random movement of electrons

Why do all substances, even nonpolar ones, experience London dispersion forces?

Because all atoms and molecules have electrons that can shift temporarily to create dipoles

How does molecular size affect London dispersion forces?

Larger molecules with more electrons have stronger LDF due to greater polarizability

Which type of intermolecular force is the weakest?

London dispersion forces (LDF)

Which type of intermolecular force is the strongest?

Hydrogen bonding

Under what condition does hydrogen bonding occur?

When hydrogen is covalently bonded to N, O, or F and is attracted to a lone pair on another N, O, or F

Give examples of bonds capable of hydrogen bonding.

N–H, O–H, and F–H

How do hydrogen bonds affect boiling and melting points?

They raise both by increasing the strength of intermolecular attractions

What molecular feature leads to hydrogen bonding in water?

The O–H bonds and the lone pairs on oxygen atoms

What is the principle of solubility summarized as?

“Like dissolves like”

Give an example of two polar substances that are miscible.

Water and ethanol

Give an example of two nonpolar substances that are miscible.

Oil and gasoline

Why are polar and nonpolar substances immiscible?

Because their intermolecular forces are incompatible — polar molecules attract each other more strongly than they do nonpolar molecules

How does polarity influence the formation of a lattice structure in solids like ice?

Hydrogen bonds create an organized lattice arrangement, increasing structure and lowering density