General Chemistry II - Kinetic Molecular Theory and Intermolecular Forces Flashcards

Flashcards on Kinetic Molecular Theory and Intermolecular Forces

Kinetic Molecular Theory

Matter is composed of tiny particles which are always in motion.

Kinetic Energy

Energy in motion.

Factors that influence the state of matter

Depends on the kinetic energy (which is a function of temperature) and intermolecular forces that exist between molecules.

Postulate #1 of Kinetic Molecular Theory

Matter is made of particles that are constantly in motion and this energy in motion is called kinetic energy.

Postulate #2 of Kinetic Molecular Theory

The amount of kinetic energy in a substance is related to its temperature. Increased temperature means higher energy & greater speed.

Postulate #3 of Kinetic Molecular Theory

There is space between particles. The amount of space between particles is related to the substance’s state of matter.

Postulate #4 of Kinetic Molecular Theory

Phase changes happen when the temperature of the substance changes sufficiently.

Postulate #5 of Kinetic Molecular Theory

There are attractive forces in between particles called intermolecular forces. The strength of these forces increases as particles get closer together.

Solids

Particles are compacted and compressed; no room for movement; can only vibrate; intermolecular forces are stronger; much denser than liquids and gases.

Liquids

Particles are also compressed; there is very little empty space between particles; molecules are held together by one or more attractive forces.

Gases

Particles are not compressed; move freely in space; space between particles is greater; attractive forces are insignificant.

Intermolecular forces

Exists between molecules whereas intramolecular forces exists between the atoms of a molecule.

London/Dispersion Forces

Temporary Dipoles, occurs in nonpolar molecules, strength of attraction is low, effect on boiling/melting points is low elevation, effect on freezing points is low elevation.

Dipole-Dipole

Permanent Dipoles, occurs in polar molecules, strength of attraction is medium, effect on boiling/melting points is medium elevation, effect on freezing points is low elevation.

Hydrogen Bonds

Permanent Polar Dipoles between H & F, O, N, occurs in polar molecules, strength of attraction is medium-high, effect on boiling/melting points is high elevation, effect on freezing points is low elevation.

Ion-Dipole

Full ion and dipole, occurs in polar molecules, strength of attraction is high, effect on boiling/melting points is high elevation, effect on freezing points is zero elevation.

Why ice floats on liquid water

In liquid water, water molecules are close together but move freely, allowing for a relatively high density. When water freezes, the molecules form a crystalline structure maintained by hydrogen bonds. This structure spaces the molecules farther apart than in liquid water, resulting in a lower density.

Biological significance of ice floating on liquid water

When ice forms on the surface of lakes and ponds, it insulates the water below, prevents the entire body of water from freezing, allowing aquatic life to survive through the winter, distributes the mixing of water layers in lakes, provides unique habitats.

Polarity

A state or a condition having both positive and negative charges, especially in case of magnetic or an electrical pole.

Electric dipole

Dipole refers to “two poles”, meaning there is a positive and negative pole within a molecule. Polar attraction happens when two opposite charges are near each other. The negative end of one molecule is attracted to positive end of the other

Physical Properties

Physical properties of substances are affected by the attractive forces between particles. Greater attraction between molecules means more energy is required to overcome these attractive forces.

INTRAMOLECULAR Forces

To form molecules which are stable, there should be sharing or transfer of electrons which is called intramolecular bonding.

INTERMOLECULAR Forces

Exists between molecules which influences the phase/state of matter and is responsible for the non-ideal behavior of gases and has more influence on condensed states of matter – liquids and solids.

Intramolecular Forces

The force that keeps those atoms stick to one another, is known as intramolecular force or interatomic force.

Intermolecular force

The force that exists between and among molecules, atoms and ions.

Coloumb’s law with Intermolecular forces

Like charges repel and unlike charges attract. And due to constant and random movement of electrons along the outer shell of an atom, a force of attraction between molecules takes place.

London Dispersion Force

The weakest among all, but present in all condensed phases of matter regardless of the nature of atoms or molecules. The only kind of IMF in symmetrical nonpolar substances like O2 and CO2 and monoatomic species like noble gas.

London Dispersion Force cause

Atoms or molecules can develop a temporary or instantaneous dipole if its electrons are asymmetrically distributed and this ‘on – the – spot dipole’ can, as a result, distort the electrons of a neighbouring atom or molecule, producing an induced dipole.

London Dispersion Force Significance

These attractive forces become significant when the species – atoms and molecules are very close. Because on the average, the valence electrons of larger atoms and molecules are farther from the attractive force of the nucleus, they exhibit larger dispersion forces. And the larger the mass the stronger is the London Dispersion Force.

Dipole – Dipole Interactions

Slight charges that are equal but opposite are created when electrons are unequally shared between constituent atoms of some molecules. Whenever the distribution of electrons is not symmetrical (asymmetrical), the molecule has a dipole moment.

Attractive Interactions of Dipole – Dipole Interactions

The molecules orient in which the slightly positive end (δ+) is near the slightly negative end (δ−).

Hydrogen Bonding or H-Bond

Occurs when the hydrogen in a molecule is bonded to a highly electronegative atom– fluorine, oxygen or nitrogen (F,O,N).

Ion-Dipole Forces

A force that acts between an ion (either cation or anion) and a polar molecule.

Ion-Dipole Forces

the dissolution process and its strength depends on the charge and size of the ion and on the magnitude of the dipole moment and size of the molecule.

Melting point

Temperature at which solid turns into liquid

Boiling point

Temperature at which a liquid turns into gas.

Melting Point and Boiling Point

Heat is needed to break the force of attraction between molecules to reach the melting or boiling point.

Solubility

The ability of a solid, liquid, or gaseous chemical substance (referred to as the solute) to dissolve in solvent (usually a liquid) and form a solution.

Why don’t water and oil mix?

Oil is composed of non-polar molecules; these molecules have no charge which are more attracted to each other than to water molecules.

Polar Molecules

Soluble in water, low volatility, Relatively high melting and boiling points for their molar mass, denser than non-polar, very few are gases, most are liquids and solids, solid have crystal lattices.

Non- Polar Molecules

Not soluble in water, Volatile, Low melting and boiling points, Not very dense, small molecules are gases; larger ones are liquids or soft solid.

London Dispersion Force Strength and Molecular Mass

The strength of London dispersion forces is stronger with increasing molecular mass as well as its melting and boiling point.

Hydrogen Bond Exception

The polar molecule with such hydrogen and electronegative atom would have the strongest van der Waals forces.

Unique physical properties of water

High surface tension, high boiling point, and low density.

Surface tension

The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules.

Density

A measure of the mass in a unit volume.

Viscosity

A measure of a fluid's resistance to flow. Higher the intermolecular forces, higher will be the viscosity.

Vapor Pressure

The pressure exerted by the gas in equilibrium with a solid or liquid in a closed container at a given temperature.