Liquids, Solids, and Intermolecular Forces (Chapter 11) – Study Notes

Liquids, Solids, and Gases: A Molecular Comparison

States of Matter: Gases, Liquids, and Solids

The physical state of a substance—gas, liquid, or solid—is determined by the arrangement and energy of its particles. Each state has distinct properties regarding shape, volume, and particle movement.

• Gas: Particles have low density, move freely, and both shape and volume are indefinite.

• Liquid: Particles are closer together, have higher density, indefinite shape, but definite volume.

• Solid: Particles are tightly packed, have high density, definite shape, and definite volume.

State	Density	Shape	Volume
Gas	Low	Indefinite	Indefinite
Liquid	High	Indefinite	Definite
Solid	High	Definite	Definite

Additional info: The state of matter is influenced by temperature and pressure, which affect particle energy and interactions.

Kinetic Molecular Theory

The kinetic molecular theory explains the behavior of particles in different states. The state of a substance depends on the balance between the kinetic energy of its particles and the intermolecular forces holding them together.

• Kinetic energy increases with temperature and tends to keep particles apart.

• Intermolecular forces work to keep particles together.

• When kinetic energy overcomes intermolecular forces, substances change state (e.g., solid to liquid, liquid to gas).

Example: Heating a solid increases particle motion, eventually overcoming attractive forces and causing melting.

Intermolecular Forces: The Forces That Hold Condensed States

Types of Forces

Intermolecular forces are the attractions between molecules, atoms, or ions, and are responsible for the physical properties of liquids and solids. They are generally much weaker than intramolecular (covalent or ionic) bonds.

• Intermolecular force: Attraction between molecules, atoms, or ions due to charges, partial charges, or temporary charges.

• Intramolecular force: Bond within a molecule, holding atoms together (e.g., covalent or ionic bonds).

Type of Force	Occurs Between	Relative Strength
Intramolecular	Atoms within a molecule	Strong
Intermolecular	Separate molecules	Weak

Example: Water molecules are held together by covalent bonds (intramolecular), but interact with other water molecules via hydrogen bonds (intermolecular).

Role of Intermolecular Forces in States of Matter

Intermolecular forces are responsible for the existence of liquids and solids. The strength of these forces determines melting and boiling points, viscosity, and other physical properties.

• Strong intermolecular forces result in higher melting and boiling points.

• Weak intermolecular forces result in substances that are gases at room temperature.

Example: Geckos can climb smooth surfaces due to intermolecular forces between their feet and the wall.

Summary Table: Properties of States of Matter

State	Particle Arrangement	Intermolecular Forces	Movement
Gas	Far apart	Weak	Rapid, random
Liquid	Close, but not fixed	Moderate	Flow past each other
Solid	Fixed, orderly	Strong	Vibrate in place

Additional info: The transition between states (melting, boiling, freezing) involves changes in kinetic energy and intermolecular forces.