Solids and Liquids

Intermolecular

Forces

Solids

Liquids

Multiple Select

which state/states of matter takes the shape of the container

• solid

• liquid

• gas

Multiple Select

which state/states of matter cannot be compressed under normal conditions

• solid

• liquid

• gas

Kinetic Molecular Theory

• Recall the kinetic molecular theory was developed to explain the

behavior of gases, the theory also applies to liquids and solids. However,
the forces of attraction between particles as well as their energy of
motion must be considered when applying the kinetic molecular theory
to the solid and liquid states.

Liquids

• Forces of attraction keep molecules closely packed

in a fixed volume, but not in a fixed position.

• Liquids are much denser than gases because of the

stronger intermolecular forces holding the particles together.

• Large amounts of pressure must be applied to

compress liquids to very small amounts.

Density & Compression

At standard temperature and pressure (25⸰C and 1 atm of pressure) liquids are much denser than gases. The density of a liquid is much greater than that of its vapor under the same conditions.

Density & Compression

• Liquid water is about 1250 times denser

than water vapor at standard temperature
and pressure, however, both particles of the liquid and the vapor have the same average kinetic energy as they are at the same temperature. The higher density of the liquid is due to the intermolecular forces that hold the particles together.

Liquids cannot be compressed unlike
gases because liquid particles are already tightly packed, and an enormous amount of pressure must be applied to reduce the volume of a liquid by a very small amount.

Liquids

Is the ability to flow and diffuse;
liquids and gases are fluids.

Fluidity

Viscosity

Is a measure of the resistance of a
liquid to flow and is determined by
the type of intermolecular forces,
size, the shape of particles, and
temperature.

• Gases and liquids are fluids because

they can flow and diffuse.

• Liquids usually diffuse more slowly

than gases at the same temperature
as the intermolecular forces of
attraction interfere with the flow,
however, liquids are less fluid than
gases.

•

The particles of a liquid are
close enough for attractive
forces to slow their movement as they flow past one another.

Liquids and Fluidity

Example
A comparison between water and natural gas leaking in a basement.
• Water remains in the basement unless the amount of water released

exceeds the volume of the basement.

• Natural gas will not stay in the basement, it will diffuse throughout the

house.

Liquids and Viscosity

Not all liquids have viscosity, scientists
discovered superfluids. Scientists cooled
liquid below -270.998⸰C and discovered
that the properties of the changed. The
superfluid helium lost viscosity (resistance
to flow).

Liquids and Viscosity

•

The stronger the intermolecular
attractive forces, the higher the viscosity.

•

In this diagram of glycerol, it is the
hydrogen bonding that makes it so
vicious.

Why is glycerol (glycerin) viscous?
The figure shows the bonding between two glycerol molecules and two
water molecules. The hydrogen atoms of each water molecule are
attached to the oxygen atoms in the two glycerol molecules forming
hydrogen bonds (strongest intermolecular force) with other glycerol
molecules.
The red dots in the figure shows where the hydrogen bonds form between molecules.

Liquids and Viscosity

Particle size and shape

Liquid A and liquid B, both have similar
attractive forces. If the molecules in
liquid A are more massive than the
molecules in liquid B, liquid A will have
greater viscosity. (The massive
molecules move on average more
slowly than the smaller molecules)

The size and shape of particles also affect viscosity.

The kinetic energy of a particle
depends on the mass and the velocity of the particle.

Temperature

Increasing the temperature decreases viscosity because the added energy allows the molecules to overcome intermolecular forces and flow more freely.

Liquids and Viscosity

Particle size and shape

Larger molecules create greater viscosity.
Long chains of molecules result in a higher
viscosity: cooking oils and motor oils.

Why do long-chain liquid molecules, such as
cooking oils and motor oils have a higher
viscosity than shorter, more compact
molecules, assuming the molecules exert the same type of attractive forces?
Within, the long chains, there is less distance
between atoms on neighboring molecules and, thus, a greater chance of attraction between atoms

Liquids and Viscosity

Why as the temperature increases the viscosity decreases?
An increase in temperature increases the average kinetic energy of the
molecules. The added energy makes it easier for the molecules to
overcome the intermolecular forces that keep the molecules from
flowing.
Suppose you pour oil into a frying pan; the oil tends not to spread across the bottom of the frying pan until you hear it.

Liquids and Viscosity

Why motor oil keeps the moving parts of an internal
combustion engine lubricated?
Because temperature changes affect the viscosity of motor oil. People used to use
different motor oil blends in winter and summer. The motor oil used in winter was
designed to flow at low temperatures and the motor oil used in summer was more
viscous so that it could maintain enough viscosity on extremely hot days or during
long trips.

Nowadays, additives in motor oil help adjust the viscosity so that the same oil blend can be used all year. Molecules in the additives are compact spheres with relatively low viscosity at low temperatures, at high temperatures, the shape of the additive molecules changes to long chains, and the chains get tangled with the oil molecules, which increases the viscosity of the oil.

Multiple Choice

What is the term for the resistance of a liquid to flow?

• fluidity

• viscosity

• temperature

Multiple Choice

As the temperature of a liquid increases, the viscosity

• increase

• decrease

• doesn't change

Multiple Choice

Water droplets are mainly formed by what force?

• Hydrogen bond

• Viscosity

• dipole-dipole

• dispersion force

Surface Tension

Intermolecular forces do not have an equal effect on all particles in a liquid.

Particles in the middle of a liquid are attracted to
particles above them, below them, and to either
side. For particles at the surface of the liquid, there are no attractions from above to balance the attractions from below. Thus, there is a net
attractive force pulling down on particles at the
surface.

The surface tends to have the smallest possible
area and to act as though it is stretched tight like the head of a drum. For the surface area to
increase, particles from the interior must move to the surface, however, it takes energy to overcome the attractions holding these particles in the area.

•

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

•

Surface tension is a measure of the inward pull by particles in the interior.

•

The stronger the attraction between particles the stronger the surface tension. Example:Water

Surface Tension

Surfactants are compounds that lower the surface tension of water.

Surface tension is why water alone will not clean
your clothes, you need soap to break down the
hydrogen bonds so the water will carry the dirt
away.

Surfactants

Water has a high surface tension because its molecules can form multiple hydrogen bonds.

Why are drops of water shaped like
spheres?
Because the surface area of a sphere is
smaller than the surface area of any other shape similar in volume.

Surfactants

How does the surface tension of the water allow the
spider to stand on top of the water?
Surface tension affects the top layer of water, causing it to behave like a stretched elastic sheet. It occurs
because the particles at the surface of the water have
no attractions from above to balance the attractions
from below, thus, there is a net attractive force pulling
down on particles at the surface.

The same forces that allow the spider to stay dry on the surface of the water also make it difficult to use water alone to remove dirt from skin and clothing.

Because dirt particles cannot penetrate the surface of the waterdrops, water alone cannot remove the dirt.

Soaps and detergents decrease the surface tension of water by disrupting the
hydrogen bonds between water molecules. When the hydrogen bonds are broken, the water spreads out allowing the dirt to be carried away by the water.

Cohesion and Adhesion

Cohesion is the force of
attraction between identical molecules.

Adhesion is the force of
attraction between
molecules that are different.

Why does the surface of the water in a narrow tube or a
straw form a meniscus (the surface dips in the center)?
Because of the two forces at work; cohesion and adhesion.
The adhesive forces between water molecules and silicon
dioxide in glass are greater than the cohesive forces
between water molecules, the water rises along the inner
walls of the cylinder.

Cohesion and Adhesion

Capillary Action

Capillary action is the upward movement of
liquid into a narrow cylinder or capillary tube.

How can paper towels absorb large
amounts of water?
Water is drawn by capillary action into the narrow spaces between the
cellulose fibers in paper towels, and
the water molecules form hydrogen
bonds with the cellulose molecules.

Multiple Choice

the interactive force that exist between water molecules and sides of a graduated cylinder is______.

• surface tension

• cohesion

• capillary action

• adhesion

Multiple Choice

Surface tension is the property of water in which...

• water spills easily.

• water molecules at the surface tend to stick together.

• water tends to be see-through.

• Water molecules in the middle tends to stay apart.

Multiple Choice

The ascension of liquids through slim tube, cylinder or permeable substance due to adhesive and cohesive forces interacting between the liquid and the surface is called_____.

• adhesion

• cohesion

• capillarity

• surface tension

Multiple Choice

Cohesion force

• Are the attraction of molecules to the container walls

• Are the attraction of molecules within a liquid

• Are important for upward movement in capillary action

Solids

Why do solids have a definite shape and volume?
There must be strong attractive forces acting between particles in a solid for a substance to be a solid rather than a liquid at a given temperature. These forces limit the motion of the particles to only vibrations around fixed locations in the solid.

Density of Solids

The particles in a solid are more closely packed than those in a liquid, therefore, most solids are denser than most liquids.
When the liquid and solid states of a substance coexist, the solid always sinks into the liquid, because it is denser than the liquid. This is because the particles in a solid are closely packed.

Solids

Why ice floats in water?
Because water is less dense as a solid than it is as a
liquid. As water freezes, each H2O molecule can
form hydrogen bonds with up to four neighboring
molecules, resulting in the molecules being far apart and less closely packed.

Solids

solids with atoms, ions, or
molecules arranged in an orderly, geometric shape.
A unit cell is the smallest
arrangement of atoms in a crystal lattice that has the same
symmetry as the whole crystal.

Crystalline solids

Amorphous solids

Solids in which the particles are
not arranged in a regular,
repeating pattern.
Amorphous solids form when
molten material cools quickly.
Rubber and many plastics are
amorphous solids.

Solids

Crystalline solids are classified into five categories based on the types of particles they contain and how those particles are bonded together.

Type

Unit Particles

Characteristics of Solid Phase Examples

Atomic

Atoms

✓Soft to very soft, ✓Very low melting points & Poor conductivity

Group 18
elements

Molecular

Molecules

✓Fairly soft, ✓Low to moderately
high melting points &
✓Poor conductivity

I2, H2O, NH3,
CO2, C12H22O11
(table sugar)

Covalent
Network Atoms connected by covalent bonds

✓Very hard, Very high melting points &✓Often poor conductivity

Ionic

Ions

✓Hard ✓Brittle, ✓High melting points &✓Poor conductivity

NaCl, KBr,
CaCO3

Metallic

Atoms surrounded by mobile valence electrons

✓Soft to hard, ✓Low to very high melting points, ✓Malleable and ductile &✓Excellent conductivity

All metallic
elements

Diamond (C) and
quartz (SiO2)

Solids

•

Carbon exists in different forms in the same state- solid, liquid, or
gas, such an element is called an allotrope.

Multiple Choice

The type of solid that has a highly arrangement of particles.

• crystalline solids

• amorphous solids

• viscous liquid

Multiple Choice

In amorphous solids, the atoms or molecules are held together in a completely random formation.

• True

• False

Classwork

Answer the following questions

(1) Liquid water is about 1250 times denser than water vapor at standard temperature and pressure. Discuss.

(2) Explain why Liquids cannot be compressed unlike gases.

(3) Compare between water and natural gas leakage in a basement.

(4) Long chain liquid molecules, as cooking oils and motor oils have a higher viscosity than shorter more compact molecules, assuming the molecules exert the same type of pressure. Discuss.

(5) Explain how motor oil keeps moving parts of an internal combustion engine lubricated

(6) Drops of water are shaped like spheres. Evaluate.

(7) Explain how the surface tension of water allow a spider to stand on the surface of water.

(8) Explain how surfactants remove dirt from clothes.

(9) Paper towels are able to absorb large amounts of water. Conclude.

(10) Ice is the solid state of water and it floats on the surface of water. Elaborate