Kinetic Molecular Model and Intermolecular Forces

Study Notes

Matter exists in three states: solid, liquid, and gas
Particles of all these states are in constant random motion
Kinetic energy is proportional to absolute temperature; higher temperature means faster particles
Solids have the slowest particle speed, followed by liquids, and gases have the fastest speed
Gas particles are more disordered than liquids and solids
Solids have minimal particle motion, primarily vibration with frequencies too fast to see
Intermolecular forces are crucial in determining the properties of solids and liquids.

Intermolecular forces (IMFs) are attractive forces between molecules
These forces are weaker than the forces holding atoms together within a molecule (intramolecular forces)
IMFs influence properties such as melting and boiling points, vapor pressure, and viscosity of substances
Several types of IMFs exist, including dipole-dipole, hydrogen bonding, ion-dipole, London dispersion forces, and dipole-induced dipole forces

Dipole-dipole forces exist between polar molecules
One end of a polar molecule (the dipole) attracts the oppositely charged end of another dipole
Polarity arises from uneven electron distribution due to differences in electronegativity between atoms in a molecule

A special type of dipole-dipole force
Occurs when hydrogen is bonded to a small, highly electronegative atom (like N, O, or F)
These bonds are relatively strong due to the high electronegativity and small size of these atoms
Hydrogen bonding is essential in determining properties of water, ethanol, etc.

Attractive forces between an ion and a polar molecule
Ions are attracted to the partial oppositely charged ends of polar molecules
This interaction is crucial for the dissolution of ionic compounds in polar solvents like water

Weakest type of IMF
Arises from temporary, instantaneous dipoles created by fluctuations in electron distribution in nonpolar molecules
The temporary dipoles induce temporary dipoles in neighboring molecules
The strength of London dispersion forces increases with increasing molecular size and surface area

Interaction between polar and nonpolar molecules
Polar molecules induce temporary dipoles in nonpolar molecules through their own dipole
This results in a temporary attraction between the polar and nonpolar molecules

Surface Tension: The resistance of a liquid to increase its surface area
Capillary Action: The ability of a liquid to flow in narrow spaces against gravity due to intermolecular forces (cohesion and adhesion)
Viscosity: The resistance of a liquid to flow. Higher viscosity means slower flow.
Vapor Pressure: The pressure exerted by the vapor of a liquid in equilibrium with the liquid at a given temperature

The temperature at which a liquid's vapor pressure equals the external atmospheric pressure
Increasing temperature increases the kinetic energy of liquid molecules, eventually overcoming intermolecular forces, allowing the liquid to boil
Higher intermolecular forces lead to higher boiling points

Liquid water is colorless, odorless, and tasteless at room temperature, turns to ice (~0 degrees C, 1 atm) and turns to steam (~100 degrees C, 1 atm)
Water's properties are unique due to hydrogen bonding
This results in: High specific heat, high boiling point, solid state (ice) is less dense than liquid water (ice floats)

Solids are classified as crystalline and amorphous.
Crystalline solids have a highly regular arrangement of particles, while amorphous solids lack a regular pattern
Crystalline solids contain a well-defined crystal lattice, a 3D structure which defines the position of individual components (atoms/ions/molecules) inside the crystal.
Different types of crystalline solids (ionic, metallic, molecular, and network) exist with different constituent components and bonds