Chem 1220: Lecture 1

Question 1

What determines the state of a substance?

Answer 1

It’s a balance between kinetic energy (keeps particles apart and moving) and attractive forces (intermolecular forces that bring molecules together).

Question 2

What are the types of intermolecular forces from weakest to strongest?

Answer 2

1. Dispersion Forces (weakest)
2. Dipole-Dipole Forces
3. Hydrogen Bonding
4. Ion-Dipole Forces (strongest)

Question 3

What is electronegativity?

Answer 3

The tendency of an atom to attract electrons in a chemical bond.

Question 4

What is bond polarity?

Answer 4

When electrons in a covalent bond are not shared equally. Can be nonpolar covalent bond or polar covalent bond, resulting in partial charges (δ+ and δ-).

Question 5

What factors affect dispersion forces?

Answer 5

1. Size of electron cloud
2. Molecular mass
3. Surface area
4. Polarizability of electron cloud.

Question 6

What is hydrogen bonding?

Answer 6

A special type of dipole-dipole force between a hydrogen atom bonded to a highly electronegative atom (N, O, or F) and another highly electronegative atom.

Question 7

Why can ionic substances dissolve in polar solvents like water?

Answer 7

Due to ion-dipole forces - interactions between ions and polar molecules that make it possible for ionic substances to dissolve in polar solvents.

Question 8

Why is water (H2O) a liquid at room temperature while oxygen (O2) is a gas?

Answer 8

H2O has hydrogen bonding (stronger IMFs) while O2 only has dispersion forces (weaker IMFs), resulting in a much higher boiling point for water (100°C) compared to oxygen (-183°C).