Niamat ullahPost Rn BScN

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The fundamental difference between states of matter is the distance between particles.

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Because in the solid and liquid states particles are closer together, we refer to them as condensed phases.

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The state a substance is in at a particular temperature and pressure depends on two antagonistic entities:

◦ The kinetic energy of the particles

◦ The strength of the attractions between the particles

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intramolecular force is any force that holds together the atoms making

up a molecule or compound. They contain all types of chemical bond. They are stronger than intermolecular forces, which are present between atoms or molecules that are not actually bonded.

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Intermolecular forces are forces of attraction or repulsion which act

between neighboring particles (atoms, molecules or ions). They are weak compared to the intramolecular forces, the forces which keep a molecule together

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Attraction between 2 oppositely charged ions◦ Ions - charged atoms

◦ formed bytransferring e-

from a metal to a nonmetal

◦ ions form a 3-D crystal lattice

NaCl

Attraction between neutral atoms◦ formed by sharing e- between two nonmetals.

◦ A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding.

◦ covalent bonds result in discrete molecules

Cl2 H2ONH3

Nonpolar Covalent Bond

• e- are shared equally

• usually identical atoms

Polar Covalent Bond

• e- are shared unequally between 2

different atoms

• results in partial opposite charges

+ -

IONIC COVALENT

Electrons

Melting

Point

Soluble in

Water

Conduct

Electricity

Other

Properties

transferred from

metal to nonmetal

high

yes

(solution or liquid)

yes

crystal lattice of ions,

crystalline solids

shared between

nonmetals

low

no

usually not

molecules, odorous

liquids & gases

The attractions between molecules are not nearly as strong as the intramolecular attractions that hold compounds together.

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They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.

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These intermolecular forces as a group are referred to as van der Waals forces.

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Van der Waals forces' is a general term used to define the attraction of intermolecular forces between molecules. There are two kinds of Van der Waals forces: weak London Dispersion Forces and stronger dipole-dipole forces.

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Intermolecular Forces

Dipole-Dipole Forces

Attractive forces between polar molecules

Orientation of Polar Molecules in a Solid

So higher dipole, larger attractive force. life saving son

A fourth type of force, ion-dipole interactions are an important force in solutions of ions.

The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents.

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Intermolecular Forces

Ion-Dipole Forces

Attractive forces between an ion and a polar molecule

Ion-Dipole Interaction

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Molecules that have permanent dipoles are attracted to each other.◦ The positive end of one is

attracted to the negative end of the other and vice-versa.

◦ These forces are only important when the molecules are close to each other.

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The more polar the molecule, the higher is its boiling point.

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While the electrons in the 1s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom.

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At that instant, then, the helium atom is polar, with an excess of electrons on the left side and a shortage on the right side.

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Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1.

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London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

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These forces are present in allmolecules, whether they are polar or non polar.

The tendency of an electron cloud to distort in this way is called polarizability.Polarizability is the ability for a molecule to be polarized. It is a property of matter

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The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger dispersion forces than short, fat ones (like neopentane).

This is due to the increased surface area in n-pentane.

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The strength of dispersion forces tends to increase with increased molecular weight.

Larger atoms have larger electron clouds, which are easier to polarize.

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The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong.

We call these interactions hydrogen bonds.

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The strength of the attractions between particles can greatly affect the properties of a substance or solution.

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Properties of Liquids

Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area.

Strong intermolecular forces

High surface tension

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Resistance of a liquid to flow is called viscosity.

It is related to the ease with which molecules can move past each other.

Viscosity increases with stronger intermolecular forces and decreases with higher temperature.

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Surface tension results from the net inward force experienced by the molecules on the surface of a liquid.

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Properties of Liquids

Cohesion is the intermolecular attraction between like molecules

Adhesion is an attraction between unlike molecules

Adhesion

Cohesion

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