General Chemistry 2
Science, Technology, Engineering, and Mathematics
Lesson 1
Kinetic Molecular
Theory of Matter

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Have you ever bought an ice cream on a hot summer
day?
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If yes, then you must
have noticed how ice
cream, when taken
out of the freezer,
takes a definite
shape, but when
exposed in the
summer heat, slowly
loses its form and
melts. 3

In this lesson, you will be learning about
theories governing the different
states of matter. You will learn the
relationship of the different
macroscopic properties of matter to
that of its molecular interactions.
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What does the kinetic
molecular theory state?

Learning Competency
At the end of the lesson, you should be able to do the following:
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Use the kinetic molecular model to explain
properties of liquids and solids
(STEM_GC11IMF-IIIa-c-99).

Learning Objectives
At the end of the lesson, you should be able to do the following:
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● Explain the kinetic molecular theory of matter.
● Compare and contrast the different states of
matter based on the kinetic molecular theory.

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● The kinetic molecular theory of matter provides an
overview of the microscopic properties of molecules or
atoms and their interactions.
● It describes the microscopic properties of matter
and how they translate to the state and other
properties of matter.
Kinetic Molecular Theory of Matter

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It states that
1. Matter is composed of small particles.
2. The molecules interact with one another through
attractive forces. The strength of these forces is
related to the distance between the particles.
Kinetic Molecular Theory of Matter

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It states that
3. These molecules are always in constant random
motion.
4. The temperature of a substance is a measure of the
average kinetic energy of the molecules.
Kinetic Molecular Theory of Matter

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Matter Is Composed of Small Particles
Kinetic Molecular Theory of Matter
Earlier atomic models

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Matter Is Composed of Small Particles
● Atoms are the building blocks of matter.
Kinetic Molecular Theory of Matter
gold bar gold atoms

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Matter Is Composed of Small Particles
● Matter can also exist as molecules.
Kinetic Molecular Theory of Matter
drop of water water molecules

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Matter Is Composed of Small Particles
● Matter can also exist as molecules.
Kinetic Molecular Theory of Matter
table salt sodium and chloride ions

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Molecules Interact through Attractive Forces
● The attractive forces between molecules are known as
the intermolecular forces.
● The stronger the interaction between two molecules,
the smaller their distance will be.
Kinetic Molecular Theory of Matter

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Molecules Interact through Attractive Forces
Kinetic Molecular Theory of Matter
solid liquid gas

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Solids
● Solids have particles with
strong intermolecular
forces such that their
particles are very close to
one another.
particles of solid

Liquids
● Liquids have intermediate
intermolecular forces.
This makes liquid particles
farther from one another
compared to those in
solids.
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particles of liquid

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Gases
● Gases have particles that are
very far apart from one
another due to weak
intermolecular forces.
particles of gas

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Molecules Are in Constant Random Motion
● All molecules are in constant random motion.
● The extent of their motion varies depending on the
temperature and strength of the interaction
between the particles.
Kinetic Molecular Theory of Matter

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Nanoscale Representation of Matter
Kinetic Molecular Theory of Matter
molecules in ice molecules in water molecules in steam

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Solids
● Solids, due to their strong
intermolecular forces, have
restricted motion.
● The particles of solids are
only able to vibrate back
and forth around a specific
point or location.
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particles of solid

Liquids
● Liquids, having
intermediate
intermolecular forces, are
able to move past each
other.
● Since their particles are still
close to one another, the
motion is restricted to
small distances as they
will collide with another
molecule.
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particles of liquid

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Gases
● Gases, having weak
intermolecular forces, are
able to move in relatively
long distances before
colliding with another
molecule.
● This happens because the
particles are very far apart
from one another.
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particles of gas

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Temperature Is a Measure of the Average KE
Kinetic Molecular Theory of Matter
heat increases
KE increases

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Matter can be described in terms of its physical state.
It can either be solid, liquid, or gas.
States of Matter
solid
(ice)
liquid
(water)
gas
(steam)

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States of Matter
State of
Matter
Shape Volume Compressibility
solid fixed shape fixed volume virtually
incompressible
liquid depends on the
container
fixed volume only slightly
compressible
gas depends on the
container
assumes the volume
of the container
very
compressible

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States of Matter
Particulate Drawings of Solid, Liquid, and Gas

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How can the kinetic
molecular theory explain
the properties of each state
of matter?

Based on the kinetic molecular theory of
matter, the state of a matter is determined
by two factors—temperature and
strength of intermolecular forces.

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As explained by KMT:
● At lower temperatures, intermolecular forces
determine the state of a substance.
● Substances with intermediate to strong
intermolecular forces will form a condensed phase,
either solid or liquid.
● Those with weak intermolecular forces will be in the
gaseous state.
Properties of the States of Matter

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How does the kinetic
molecular theory explain
phase changes?

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● Recall that a higher temperature means a higher
average kinetic energy.
● This means that the particles will have enough energy
to move around faster.
● Increasing the temperature also weakens the
intermolecular forces of attraction.
Phase Changes

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Melting
● The molecules in ice vibrates
back and forth to a specific
location since it is in the
solid phase.
● Increasing the temperature
will provide enough kinetic
energy to overcome their
strong intermolecular forces.
● The solid becomes a liquid in
a process called melting.

Vaporization
● When liquid water is
heated, its particles are able
to move past one another
in relatively longer
distances.
● The process in which liquid
is converted to a gas is
called vaporization.
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Did You Know?
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Ice-skating is
possible since the
molecules in ice are
farther apart than
they are in liquid
water.

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How does the kinetic molecular theory
describe phases and phase changes?

Let’s Sum It Up!
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● The kinetic molecular theory states that:
○ Matter is composed of small particles.
○ The molecules interact with one another through
attractive forces. The strength of these forces is
related to the distance between the particles.
○ These molecules are always in constant random
motion.
○ The temperature of a substance is a measure of the
average kinetic energy of the molecules.

Let’s Sum It Up!
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● Solids have particles with strong
intermolecular forces that cause the
particles to be close together.
● This causes the particles’ motion to be
restricted to vibrations.

Let’s Sum It Up!
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● Liquids have particles with intermediate
intermolecular forces that cause the
particles to be farther apart from each other
than in solids.
● This allows the particles to move about but
in relatively short distances.

Let’s Sum It Up!
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● Gases have particles with negligible
intermolecular forces that cause the
particles to be very far apart from one
another.
● Due to the large distances between particles,
the molecules are able to move in long
distances.

Let’s Sum It Up!
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● The average kinetic energy of the molecules
can be measured by determining the
temperature.

Let’s Sum It Up!
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● The physical state of matter is affected by
both kinetic energy and intermolecular
forces.
○ At low temperatures, intermolecular forces
dominate.
○ At high temperatures, the molecules have higher
kinetic energy and will be able to overcome the
intermolecular forces present.

Challenge Yourself
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Describe the phase changes using the
kinetic molecular theory. Evaluate
whether the changes require an
increase or decrease in temperature.

Bibliography
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Brown T.L. et al. Chemistry: The Central Science. Pearson Prentice -Hall, 2005.
Boundless. “Kinetic Molecular Theory and Gas Laws.” Boundless Chemistry. Accessed August 12,
2016. https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/gases-
5/kinetic-molecular-the
Chang, Raymond, and Kenneth A. Goldsby. General Chemistry: the Essential Concepts. New York:
McGraw-Hill, 2014.
Petrucci, Ralph H. General Chemistry: Principles and Modern Applications. Toronto, Ont.: Pearson
Canada, 2011. Print.
Silberberg, Martin S. Principles of General Chemistry. New York: McGraw-Hill, 2013.