Intermolecular Forces and States of Matter

General Chemistry II - Chapter 1: Kinetic Molecular Model and Intermolecular Forces of Attraction in Matter

• This chapter explores the kinetic molecular theory and intermolecular forces governing the properties of solids and liquids.
• The kinetic molecular theory explains the properties of solids and liquids in terms of intermolecular forces of attraction.
• Matter exists in three fundamental states: solid, liquid, and gas.
• Solids have a fixed shape and volume. Molecules in a solid are closely packed and vibrate in fixed positions, with limited motion.
• Liquids have a fixed volume but take the shape of their container. Molecules in a liquid are close together but can move past each other, with greater freedom of motion than in solids.
• Gases have neither a fixed shape nor a fixed volume. They expand to fill the container they occupy. Molecules in a gas are far apart and have high speeds and complete freedom of motion.

Section 1.1: Kinetic Molecular Theory of Solids and Liquids

• The kinetic molecular theory explains the properties of solids and liquids.
• All matter is composed of tiny particles in constant motion.
• Particle speed is proportional to temperature. Increased temperature leads to greater molecular speeds in solids, liquids, and gases.
• Different phases differ in the distances between particles, in the freedom of motion of particles, and in the extent to which particles interact.

Kinetic Molecular Theory

• All matter is made up of tiny particles.
• These particles are in constant motion.
• The speed of the particles is proportional to the temperature.
• Increased temperature means greater distances between particles, greater freedom of motion, and greater extent of particle interactions in solids, liquids, and gases.

States of Matter

• Solid: Fixed shape and volume. Particles packed closely together, vibrating in fixed positions.
• Liquid: Fixed volume but takes the shape of its container. Particles close together but can move past each other.
• Gas: Neither fixed shape nor volume. The particles are far apart and move freely.

Activity 1

• Compare distances among molecules in solids, liquids, and gas, ranking them in order of increasing distance.
• Describe the characteristic movement of molecules in each state (solid, liquid, gas).
• Describe the arrangements of molecules in each state.
• Arrange the three phases of matter in order of increasing volume of empty space between the molecules.

Properties of Matter

• Volume/Shape: Gases fill the entire volume of their container, liquids maintain a fixed volume but assume the shape of the container, and solids maintain both fixed volume and shape.
• Density: Solids > Liquids > Gases.
• Compressibility: Gases are highly compressible, liquids are essentially incompressible, and solids are almost incompressible.
• Molecular Motion: Solids – vibration, Liquids – molecules can move past each other, Gases – particles have high speeds and move randomly in all directions.

Intermolecular Forces of Attraction

• Intermolecular forces are attractive forces between molecules or particles in solids or liquids.
• These forces are weaker than the forces within molecules (intramolecular forces).
• The attractive forces collectively categorized under "van der Waals forces".

Types of Intermolecular Forces

• Dipole-Dipole: Attraction between oppositely charged ends of polar molecules.
• Hydrogen Bonding: Strong dipole-dipole interaction between a hydrogen atom covalently bonded to a small, highly electronegative element (e.g., O, N, F). This is a special type of dipole-dipole attraction.
• Ion-Dipole: Interaction between an ion (positive or negative) and a polar molecule. Explaining ionic compounds solubility in polar molecules like water.
• London Dispersion Forces: Weakest intermolecular force, resulting from temporary, instantaneous dipoles due to uneven electron distribution in nonpolar molecules or in nonpolar regions of larger molecules.
• Dipole-Induced Dipole: Interaction between a polar molecule and a nonpolar molecule, where the polar molecule induces a temporary dipole in the non-polar molecule.

Activity 2

• Determine the type of intermolecular force present in various substances (e.g., SO2, N2, HF, CO2, Ne, MgCl2 dissolved in H2O).
• Justify the determination of the type of intermolecular force in individual substances.

Section 1.3: Intermolecular Forces and Properties of Liquids

• Liquids lack a simple or regular structure
• Properties of liquids are examined at a particulate level
• Capillary action, surface tension, vapor pressure, and boiling point of liquids are explained by their intermolecular forces.

Surface Tension

• The elastic force in the surface of a liquid.
• Energy required to increase the surface area of a liquid by a unit area.
• Manifested as a skin-like effect on the surface of the liquid.
• Allows small objects to float on the surface of water, like needles and paper clips, and helps explain the shape of water droplets. Liquids with stronger intermolecular attractions generally exhibit higher surface tension.

Capillary Action

• The tendency of liquids to rise in narrow tubes or be drawn into small openings.
• A result of intermolecular attraction between the liquid and solid materials.
• Explains how water moves up plants or how liquids are drawn into narrow capillaries or tubes. Two driving forces: cohesion (attraction between liquid molecules) and adhesion (attraction between liquid and container wall materials).
• The relative strength of cohesion versus adhesion determine whether the liquid surface is convex or concave inside the capillary.

Viscosity

• The resistance of a liquid to flow.
• Described as the thickness or thinness of a liquid.
• Liquids with stronger intermolecular forces tend to have higher viscosity. Longer chained molecules have higher viscosity.

Vapor Pressure

• The pressure exerted by the vapor of a liquid (or solid) in equilibrium with the liquid (or solid) phase.
• The vapor pressure is affected by temperature. Increased temperatures increase vapor pressure.
• The substance has a relatively strong vapor pressure where its molecules are relatively weaker. Stronger intermolecular attractions decrease vapor pressure

Boiling Point

• The temperature at which the vapor pressure of a liquid equals the external pressure.
• The higher the external pressure , the higher the boiling point.
• Intermolecular forces influence the amount of energy needed for the liquid to reach its boiling point. Stronger intermolecular forces result in a higher boiling point.

Heat of Vaporization

• The amount of energy required to vaporize one mole of a substance at its boiling point.
• Energy application to a liquid disrupting intermolecular forces allowing the molecules to enter a gaseous state. The stronger the intermolecular forces, the higher the heat of vaporization.

Structure and Properties of Water

• At room temperature, pure water is a colorless, odorless, and tasteless liquid.
• Solid water (ice) is less dense than liquid water. Its solid form has an open structure due to hydrogen bonding, increasing the space between molecules.
• Water has unusual high values for heat capacity and heat of vaporization due to hydrogen bonding.

Types and Properties of Solids

• Solids are classified as crystalline or amorphous based on the arrangement of their particles.
• Crystalline solids have a highly ordered arrangement of particles with a defined crystal structure, while amorphous solids have disorder in their structure.

Phase Changes

• Phase changes are transformations of matter from one physical state (solid, liquid, gas) to another.
• Phase changes involve changes in the molecules' order.

Phase Diagrams

• A visual representation of the pressure and temperature conditions under which a substance can exist in different physical states – solid, liquid, vapor.
• Phase diagrams can be used to determine if a substance will exist as a solid, liquid or gas at certain temperatures and pressures.

Features of Phase Diagrams

• Phase diagrams show different phases of substance at various pressure and temperatures.
• The curves/lines dividing the phases represent points of equilibrium among the different phases.
• The triple point is the specific temperature and pressure where three phases coexist (solid, liquid and gas). It's the combination of pressure and temperature where all three phases exist at equilibrium.
• The critical point is the temperature and pressure beyond which the liquid and gas phases merge into a supercritical fluid.

Test your knowledge of intermolecular forces (IMFs) and their effects on the states of matter. Questions cover the Kinetic Molecular Theory, IMF types and strength, phase arrangement, hydrogen bonding, solubility, capillary action, and more.