Each state of matter, from a microscopic viewpoint, can be described by:

•The distance between the constituent units.

•The attractive forces within and

between the constituent units.

•The motion of the constituent units within

the substance.

•The orderly arrangement of the constituent units

within the substance.

Why is learning, about the structure of

substances, so important?

Well, ask yourself these questions: •Can the graphite in a pencil become a diamond? (They are both made up of the same building material - Carbon).

•How does a virus, that once only affected an animal, turn into a deadly virus for humans?

Understanding the structure of materials provides the answers to these questions!!!!!!!

•The motion of their particles is that they can only vibrate = very low kinetic energy.•The distance between the particles is very small = very low potential energy.•The attractive forces between the particles is very good = very low potential energy.

•The degree of disorder (entropy) is very small.

Properties of the

Solid State, continued:

• Possess a definite shape.

• Possess a definite volume.

• Cannot be compressed unless under extremely high pressures.

• Possess an extremely slow diffusion rate = very low kinetic energy.

(Diffusion is the ability to mix naturally without external forces.)

Solids at room temperature:

1. All Ionic compounds

2. All Covalent network substances.

3. All metals (except mercury).

4. All Molecular compounds if they have a large molecular mass.

* all light to medium-massed molecules exist as gases

or liquids depending upon the strength of their

inter-particle attractive forces.

•Their particles’ motion capabilities are not only vibrations, but also rotation abilities and restricted translation ability = medium kinetic energy.

•They also have very small distances between their particles so are not compressible under ordinary pressures = medium potential energy.

•They have medium forces of attraction between those particles = medium potential energy.

Properties of the Liquid State, continued:

• Possess an indefinite shape.

• Possess a definite volume.

• Medium diffusion rate =

medium Kinetic Energy.

•They have mediocre

entropy for their

degree of disorder.

More interesting properties/terms of the liquids:

Viscosity: The resistance to flow (opposite of fluidity)

Depends on the size, shape, and chemical nature of the molecules.

In general:

• the greater the inter-molecular forces, the greater the viscosity.

• the greater the molecular mass, the greater the viscosity.

• the lower the KE, the greater the viscosity.

Surface Tension:

Is a property of a liquid that imparts membrane-like behavior to its surface.

The larger the inter-molecular forces, the greater the surface tension.

It is the reason that a needle can be supported on the surface of a glass of water. COHESION! (remember “H-bonding”)

“Wetting” occurs when the attractive forces between a liquid and a solid particle is greater than the internal cohesive forces in the liquid.

Capillary Action: the attraction between glass and water

The meniscus of a liquid is determined by its surface tension and its interaction with its container.

Water has a concave meniscus.

The surface of glass contains Si - O - H groups. As a result, the water appears to crawl up the glass walls creating a negative or concave meniscus.

A Convex Meniscus

Mercury is nonpolar by nature and has very strong bonds between the mercury atoms and so there is no significant attraction between them and the glass. Thus, mercury tends to pull away from the glass surface and you get a positive meniscus.

GAS:

•They have all kinds of motion ability- vibrational, rotational, and unrestricted translational = high kinetic energy.

•They have huge distances between their particles - 1000 times greater than their own diameter = high potential energy.

•The attractive forces between their particles are considered negligible = high potential energy.

Properties of the gases:

•Do not have a definite volume or shape.

•Fastest diffusion rate = greatest kinetic energy.

•Greatest distance between their particles = greatest potential energy.

•They have very high entropy for their degree of disorder.

Gases:

Examples of a Liquid and a Gas at room temperature:

Many molecular compounds are either liquids or gases at room temperature, unless of course they have a very high molecular mass.

# 1: Water (melts at 0 °C, boils at 100 °C) so is a liquid at room temperature.

#2: Nitrogen (melts at -210 °C and boils at -195 °C) so, is definitely a gas at room temperature.

Have you figured out how KE and PE are related to structure

and motion?KE = related to the motion of the particles. The faster a molecules velocity the greater the KE (directly proportional). KE = 0.5 mv2

PE = related to the distance between the particles making up the substance. The greater the distance the greater the PE (directly proportional). PE is also related to the number and strength of the attractive forces between the particles. The greater the number and/or strength of the forces the LOWER the PE (inversely proportional).

Chemical reactions are dependent upon:

•Specific characteristics of the type of particles (atoms, ions, or molecules) that make up the reactants.

•Total energy of the reactants which can be related to the physical state of the reactants

A comparison of the States of Matter

The Chart: Starting with Ionic Crystals

Particles in Crystals:

+ and - ions

Principal Attractive forces between the particles:

Very strong electrostatic attractions between the ions

Melting points and boiling points:

High

Ionic Crystals, Continued:

Electrical conductivity in liquid/solid state:

High/none

Characteristics of crystal:

Hard and brittle. Most dissolve in polar solvents.

Conditions of Formation:

EN value difference 1.8 or higher.

Ionic Examples

CaCO3 has a MP = 1339 °C (102.5 atm)

NaCl has a MP = 804 °C)

The Chart: The Covalent Network Crystals

Particles in Crystals:

Atoms (the whole crystal is one giant macromolecule.

Principal Attractive forces between the particles:

Covalent bonds that are very strong.

Melting points and boiling points:

High.

Covalent Network, Continued:

Electrical conductivity in liquid/solid state:

Depends, see examples

Characteristics of crystal:

Very hard and insoluble in most liquids.

Conditions of Formation:

Most formed by elements in Family 14.

A Covalent Network Crystal Example

More covalent examples:

The carbon atoms in graphite are strongly joined by covalent bonds, but only within a plane, unlike the 3D network of bonds in diamond. These planes of carbon atoms simply stack together one on top of the other, with only very weak forces between them. The planes of carbon atoms can then easily slip over each other, and graphite is therefore an important lubricant !

Synthetic diamonds can be made at 2700 C and a pressure of 800,000 lbs./sq.inch

The Chart: Metallic Crystals

Particles in Crystals:

+ metal atom kernels plus mobile electrons (remember “hot potato)

Principal Attractive forces between the particles:

Metallic bonds which are strong.

Melting points and boiling points:

Most are high.

Metallic Crystals, Continued:

Electrical conductivity in liquid/solid state:

High/High

Characteristics of crystal:

Most are hard, malleable, ductile, and tenacious. Conductive of heat. Soluble in other metals (alloys). Insoluble in most liquids.

Conditions of Formation:

Made of atoms on the left side of chart = low EN values.

Metallic Crystal Examples

Gold’s MP = 1064 °C and its BP = 2808 °C.

Tungsten’s MP = 3410 °C and its BP = 5900 °C.

The Chart: Polar Covalent Crystals.

Particles in Crystals:

Polar molecules.

Principal Attractive forces between the particles:

Electrostatic attraction between dipoles = intermediate strength. H bonds being the strongest.

Melting points and boiling points:

Intermediate

Polar Molecular Crystals, Continued:

Electrical conductivity in liquid/solid state:

Very low for both states.

Characteristics of crystal:

Transparent,brittle, break very easily (even more so than ionic). Soluble in polar solvents.

Conditions of Formation:

Asymmetricalmolecules with polar covalent bonds (0.5-1.7 EN difference).

Polar Covalent Crystal Example

The Chart: The Nonpolar Covalent Crystals.

Particles in Crystals:

Atoms or nonpolar molecules.

Principal Attractive forces between the particles:

London dispersion (Van der Waals)

Melting points and boiling points:

Low

Nonpolar Molecular Crystals, Continued:

Electrical conductivity in liquid/solid state:

Extremely low for both.

Characteristics of crystal:

Very soft. Soluble in nonpolar solvents and in solvents that are nonpolar/polar.

Conditions of Formation:

Symmetrical molecules or those with nonpolar bonds (EN difference of 0.4 or lower).

Nonpolar Covalent Crystal Examples

While a saturated fatty acid is a straight molecule on the average, the double bond in an unsaturated fatty acid produces a kink in the molecule. Due to these kinks, unsaturated fatty acids don't pack together as compactly, making them more “fluid” at room or body temperature.