kinetic mol theory.pptx

Kinetic Molecular Model of
Liquids and Solids

Matter can exist in three main different states: namely, solid, liquid,
and gas. The most common example of which is water. You only have
to think about water to appreciate how different the three states of
matter are. Steam bathing, drinking, and ice skating are all done in
contact with water in its various forms. But how do these states of
matter differ from each other? Understanding the kinetic molecular
model of the three states will answer this question.

Kinetic Molecular Theory
The Kinetic Molecular Theory (KMT) is a model used to explain
the behavior of matter. It is based on a series of postulates.
Some of the postulates of KMT are as follows:
 Matter is made of particles that are constantly in motion. This energy in motion is
called kinetic energy.
 The amount of kinetic energy in a substance is related to its temperature.
 There is space between particles. The amount of space in between particles is
related to the substance's state of matter.
 Phase changes happen when the temperature of the substance changes
sufficiently.
 There are attractive forces in between particles called intermolecular forces. The
strength of these forces increases as particles get closer together.

Figure 1: A Representation of the
Solid, Liquid, and Gas States. (a)
Solid O2 has a fixed volume and
shape, and the molecules are packed
tightly together. (b) Liquid
O2 conforms to the shape of its
container but has a fixed volume; it
contains relatively densely packed
molecules. (c) Gaseous O2 fills its
container completely—regardless of
the container’s size or shape—and
consists of widely separated
molecules. (https://bit.ly/3hrR4PX)

FOCUS: The Condensed State: Liquids and Solids
 In liquids, the molecules are so close together that there is very little empty
space between them. Liquids are much more difficult to compress, and they are
much denser at normal conditions.
 Molecules in a liquid are held together by one or more types of attractive forces.
However, the molecules can move past one another freely. Liquids can flow, can
be poured and assumes the shape of its container.
 In a solid, molecules are held tightly in position with virtually no freedom of
motion. There is even less empty space in a solid than in a liquid.
 Solids are almost incompressible and possess definite shape and volume.

Compare the properties of solids and liquids by completing the table based on the
kinetic molecular model. Provide a short description of each characteristic for the
given state of matter
CHARACTERISTIC SOLID LIQUID
Intermolecular force
Shape
Volume
Density
Compressibility
Arrangement of particles
Motion of molecules
Fluidity

Types of Intermolecular Forces
 Intermolecular Forces
are attractive forces that act between molecules or
particles in the solid or liquid states. Generally, these
attractive forces are much weaker than bonding forces.
The different types of intermolecular forces are the
following:
I. London Dispersion forces – these forces of
attraction result from temporary dipole moments
induced in ordinarily nonpolar molecules.

 These forces are present between all types of molecules due to the movement of
electrons.
 As electrons move around the nucleus, an uneven distribution causes momentary
charge separations. Slightly positive sides of a molecule are attracted to the slightly
negative sides of the adjacent molecule.
 An Illustration of London Dispersion Forces using Helium atoms (2 electrons)

Dipole-dipole forces are attractive forces between polar
molecules (molecules that possess dipole moments).
• In polar molecules the electrons are unevenly distributed because some elements are more
electronegative than others. The partial negative side of one molecule is attracted to the partial
positive side of another molecule.
• This type of force is stronger than the dispersion forces because polar molecules have a
permanent uneven distribution of electrons. The nature of attraction is electrostatic and can be
understood in terms of Coulomb’s law: The larger the dipole moment, the stronger the attraction.

III. Hydrogen bond is a special type of dipole-dipole interaction between the
hydrogen atom in a polar bond, such as N‒H, O‒H, or F‒H, and an electronegative
O, N, or F atom.
 Hydrogen bonds between water molecules are
particularly strong.
 The interaction is written as A ‒ H ••• B or A ‒ H
••• A
A and B represent O, N, or F; A ‒ H is one
molecule or part of a molecule and A or B is a
part of another molecule; the dotted line
represents the hydrogen bond.
 Examples of hydrogen bonding in water (H2O),
ammonia (NH3) and hydrogen fluoride (HF):

 Factors Affecting Strength of Intermolecular Forces
Melting points and boiling points of substances can be used as indicators of strength of
intermolecular forces operating in given solids and liquids.
When a solid melt, or a liquid boil, the particles move away from each other. As they do,
intermolecular forces of attraction are broken. The stronger the intermolecular forces to be broken,
the larger the amount of energy needed to break them, hence, the higher the melting point for
solid to liquid transformation, and boiling point for liquid to gas transformation.

Crossword Puzzle
Directions: Complete the crossword by filling in the boxes to form a word that fits each clue.
Disregard space between two-word phrases or hyphens.
1. This is a special case of a very strong
dipole-dipole interaction.
4. The force that holds atoms together in
a molecule.
6. Intermolecular forces present among
symmetrical nonpolar substances.
8. The attractive force between
molecules.
Down:
2. This is an intermolecular force that acts
between an ion and a polar molecule.
3. A collective term used to define the
attraction of intermolecular forces.
5. These are attractive forces between
polar molecules.

Properties of Liquids
The properties of liquids that were observed are consequences of the interactions of
particles that make up the liquid.
I. Surface Tension- is the measure of the elastic force in the surface of a liquid.

 It is the amount of energy required to stretch or increase the surface of a liquid by a
unit area.
 It is manifested as some sort of skin on the surface of a liquid or in a drop of liquid.
 Molecules within a liquid are pulled in all directions by intermolecular forces.
Molecules at the surface are pulled downward and sideways by other molecules, not
upward away from the surface.
 These intermolecular forces tend to pull the molecules into the liquid and cause the
surface to tighten like an elastic film or “skin”.
 Liquids that have strong intermolecular forces also have high surface tension.

I. Viscosity- is a measure of a fluid’s resistance to flow. The greater the viscosity, the slower the
liquid flows.
It is expressed in units of centipoise. The table below
gives viscosities of liquids of some pure substances.
Water has viscosity of 1 centipoise or 0.001 Pa/s at 20oC.
Substances with lower viscosities include carbon
tetrachloride and benzene. Glycerol has a resistance to
flow of more than a thousand times greater

• Liquids that have strong
intermolecular forces have higher
viscosities than those that have weak
intermolecular forces.
• Viscosity decreases as
temperature increases: hot molasses
flows much faster than cold
molasses. The viscosities of some
familiar liquids in the table beside
were measured at 20 OC, except for
lava (ranges between 700 to
1200OC.
Table 2. Viscosities of some common liquid

III. Vapor Pressure
• The equilibrium vapor pressure is the
maximum vapor pressure of a liquid at a given
temperature and that it is constant at a constant
temperature. It increases with temperature.
• When temperature is high, more molecules
have enough energy to escape from the liquid.
At a lower temperature, fewer molecules have
sufficient energy to escape from the liquid
• The stronger the intermolecular forces of
attraction, the lower the vapor pressure of a
liquid.
Figure 7. Vapor pressure of water vs.
temperature, adapted from Teaching Guide
for SHS General Chemistry 2, CHED and
Philippine Normal University

IV. Boiling point- is the temperature at which the
vapor pressure of a liquid is equal to the external
pressure.
• A liquid boil when its vapor pressure equals the
pressure acting on the surface of the liquid.
• The normal boiling point is the temperature at
which the liquid converts to a gas when the external
pressure is 1 atm. The normal boiling point of water
is 100oC.
• The boiling points of substances often reflect
the strength of the intermolecular forces operating
among the molecules. At the BP, enough energy
must be supplied to overcome the attractive forces
among molecules before they can enter the vapor
phase.

V. Molar Heat of Vaporization
• The molar heat of vaporization (ΔHvap) is the energy required to vaporize 1 mole of a liquid at a given
temperature. H is the symbol for enthalpy, which means heat content at a given standard condition.
• The heat of vaporization may be considered a measure of the strength of intermolecular forces in a
liquid. If the intermolecular attraction is strong, it takes a lot of energy to free the molecules from the liquid
phase and the heat of vaporization will be high.
• It is easier to vaporize acetone (lower Hvap) than water (higher Hvap) at a given temperature, and more
acetone escapes into the vapor phase at a given temperature. Acetone is a polar substance but has no H-
bonding. It has weaker intermolecular forces than water, and therefore acetone molecules are held less
tightly to one another in the liquid phase.
• A practical way to demonstrate differences in the molar heat of vaporization is by rubbing acetone on
your hands. Compare what is felt when water is used. Acetone has a lower ΔHvap than water so that heat
from our hands is enough to increase the kinetic energy of these molecules and provide additional heat to
vaporize them. As a result of the loss of heat from the skin, our hands feel cool.

True or False. Write TRUE is the statement is correct and FALSE if otherwise.
1. The vapor pressure is higher for a substance with stronger IMFA.
2. The boiling point of a substance is directly proportional to its heat of vaporization.
3. The normal boiling point is the boiling point of the liquid when the vapor pressure is 1 torr.
4. Acetone has a higher ΔHvap than water.
5. When temperature is high, more molecules have enough energy to escape from the liquid

2. Although steel is denser than water, a steel needle or paper clip placed carefully lengthwise on
the surface of still water can be made to float. Explain at a molecular level how this is possible:

Water: A Very Unusual Liquid
Structure and Properties of Water
Water is an essential substance to life. It is the
most abundant compound on earth and comprises
about more than 60% of the human body. But it is
also one of the most unusual substances on earth.
At room temperature, pure water is a colorless,
odorless, and tasteless liquid. It turns to ice, its
solid form, at 0OC and 1 atm. At 100OC, it
becomes gas, commonly termed steam.
• Water is a good solvent.
A unique property of water is its ability to dissolve a large variety of chemical substances. It
dissolves salts and other ionic compounds, as well as polar covalent compounds such as alcohols
and organic substances that can form hydrogen bonds with water. Gases like oxygen and carbon
dioxide will dissolve in water meaning that some animals do not need to breathe air to respire
but they must still be able to absorb oxygen and excrete carbon dioxide. Water is sometimes
called the universal solvent because it can dissolve so many things.

• Water has a high specific heat.
(Specific heat is the amount of heat or energy needed to raise the temperature of one gram
of a substance by 1oC) The specific heat of water is 1 calorie/g-oC (4.18 J/g-oC), one of the
highest for many liquids. Water can absorb a large amount of heat even if its temperature
rises only slightly. To raise the temperature of water, the intermolecular hydrogen bonds
should break. The converse is also true; water can give off much heat with only a slight
decrease in its temperature. This allows large bodies of water to help moderate the
temperature on earth.
• The boiling point of water unusually high
Many compounds similar in mass to water have much lower boiling points. The strong intermolecular
forces in water allow it to be a liquid at a large range of temperatures.
• Solid water is less dense, and in fact floats on liquid water.
Unlike all other liquids, the molecules in solid water are farther apart than they are in liquid water. When
solid water forms, the hydrogen bonds result in a very open structure with unoccupied spaces, causing the
solid to occupy a larger volume than the liquid. This makes ice less dense than liquid water, causing ice to
float on water.

1. Water is a good solvent
Relate this property to the role of water in plant nutrition
Answer: __________________________________________________________________
2. Water has a high specific heat.
Relate this property to changing climate and the capacity of bodies of water to act as
temperature buffer:
Answer: __________________________________________________________________
3. The boiling point of water unusually high
Relate this property to questions on small water bodies drying up:
Answer: __________________________________________________________________
4. Solid water is less dense, and in fact floats on liquid water.
Relate this property to the survival of aquatic organisms in temperate countries:
Answer: __________________________________________________________________
Answer the following questions:

Solids and their Properties
A solid is like a liquid in that particles are in contact with each other. Solids are unlike liquids
in that the intermolecular forces are strong enough to hold the particles in place. At low
enough temperatures, all substances are solids (helium is the lone exception), but the
temperature at which the solid state becomes the stable phase varies widely among
substances, from 20 K (−253°C) for hydrogen to over 3,900 K (3,600°C) for carbon.
General Types of Solids
Solids can be categorized into two groups: the
crystalline solids and the amorphous solids.
The differences in properties of these two groups of
solids arise from the presence or absence of long-
range order of arrangements of the particles in the
solid.

Features that can be used to distinguish a crystalline solid from an amorphous solid.
• Arrangement of particles
The components of a solid can be arranged in two general ways: they can form a regular repeating
three-dimensional structure called a crystal lattice, thus producing a crystalline solid, or they can
aggregate with no particular long-range order and form an amorphous solid (from the Greek
ámorphos, meaning “shapeless”).
1. Crystalline solids are arranged in fixed geometric patterns or lattices. Examples of crystalline solids
are ice and sodium chloride (NaCl), copper sulfate (CuSO4), diamond, graphite, and sugar
(C12H22O11). The ordered arrangement of their units maximizes the space they occupy and are
essentially incompressible.
2. Amorphous solids have a random orientation of particles. Examples of amorphous solids are glass,
plastic, coal, and rubber. They are considered super-cooled liquids where molecules are arranged in a
random manner similar to the liquid state.

• Behavior when heated
The presence or absence of long-range order in the structure of solids results in a difference in the
behavior of the solid when heated.
a) The structures of crystalline solids are built
from repeating units called crystal lattices. The
surroundings of particles in the structure are
uniform, and the attractive forces experienced
by the particles are of similar types and
strength. These attractive forces are broken by
the same amount of energy, and thus, crystals
become liquids at a specific temperature (i.e.
the melting point). At this temperature,
physical properties of the crystalline solids
change sharply.

b) Amorphous solids soften gradually when they are heated. They tend to melt over
a wide range of temperature. This behavior is a result of the variation in the
arrangement of particles in their structures, causing some parts of the solid to melt
ahead of other parts.

Identify the following samples of solids as AMORPHOUS or CRYSTALLINE.
1. Diamond ________________________
2. Plastic ________________________
3. Alum ________________________
4. Gel ________________________
5. Mica ________________________
6. Polymer ________________________
7. Rock salt ________________________
8. Snowflakes ________________________
9. Glass ________________________
10. Wax ________________________
Describe the difference in structure of crystalline and amorphous solids through a graphic
organizer.

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