General
Chemistry 2
Quarter 3 – Week 1 - Module 1
Kinetic Molecular Model
Target
The lesson explores the kinetic molecular theory and how it pertains
to the properties of solids and liquids. You'll learn the Kinetic Molecular Theory
explains the properties of solids and liquids in terms of intermolecular forces of
attraction and the kinetic energy of the individual particles. After reading this
learning material, you are expected to:
Use the kinetic molecular model to explain properties of liquids and
solid STEM_GC11IMFIIIa-c-99)
Describe and differentiate the types of intermolecular forces
(STEM_GC11IMFIIIa-c-100)
Before going on, check how much you know about this topic.
Answer the pretest on the next page and write your answer in
¼ sheet of paper.
JUMPSTART
Direction: Select the letter of the correct answer and write in ¼ sheet of paper.
1. Which of the following is NOT a characteristic of liquids?
A. Liquids have the ability to flow.
B. The particles of a liquid are not attracted to each other.
C. The particles of liquids are closer together than particles of gases.
D. Liquids conform to the shape of their container.
2. Which of the following explains that liquids cannot be compressed easily?
A. The particles are too far apart.
B. The particles are arranged in a fixed position.
C. The particles are too close together to be squished any closer.
D. The particles are free to move and simply move away from each
other when we try to squish them
3. When NaCl dissolves in water, aqueous Na+ and Cl ions result. What do you
call the force of attraction that exists between Na+ and H2O?
A. dipole-dipole
C. hydrogen bonding
B. ion-ion
D. ion-dipole
4. Which of the following is NOT a characteristic of liquids?
A. Liquids have the ability to flow.
B. The particles of a liquid are not attracted to each other.
C. The particles of liquids are closer together than particles of gases.
D. Liquids conform to the shape of their container.
5. Kinetic-molecular theory makes several assumptions about _______________.
A. The size and energy of the molecules.
B. The motion and energy of the molecules.
C. The motion and size of the molecules
D. The size and weight of the molecules
Discover
Kinetic Molecular Theory
Take a glass of water. Drop a few drops of red food coloring in it. What happens?
The red food coloring drops should make their way down the glass of water slowly,
spread out and finally tint all of the water a reddish color. Why does this happen?
It happens because both substances are made out of molecules that are constantly
moving. These molecules have energy; one of the fundamental principles of the
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 increase as particles get closer together.
Now, let us investigate two kinds of forces, or attractions, that operate in a
molecule—intramolecular and intermolecular. Intramolecular forces are the
forces that hold atoms together within a molecule. Intermolecular forces are forces
that exist between molecules.
INTERMOLECULAR FORCES (IMF) are relatively weaker than the
forces within the molecules forming bonds (intramolecular forces) Intramolecular
Forces hold atoms together in a molecule. The intermolecular forces of attraction in
a pure substance are collectively known as van der Waals forces; Dipole-dipole,
Hydrogen bonding, Ion-dipole, London dispersion
1. Dipole-dipole forces. These forces occur when the partially positively charged part
of a molecule interacts with the partially negatively charged part of the neighboring
molecule. The prerequisite for this type of attraction to exist is partially charged
ions—for example, the case of polar covalent bonds such as hydrogen
chlorideDipole-dipole interactions are the strongest intermolecular force of attraction.
2. Hydrogen bonding: This is a special kind of dipole-dipole interaction that occurs
specifically between a hydrogen atom bonded to either an oxygen, nitrogen, or
fluorine atom. The partially positive end of hydrogen is attracted to the partially
negative end of the oxygen, nitrogen, or fluorine of another molecule. Hydrogen
bonding is a relatively strong force of attraction between molecules, and
considerable energy is required to break hydrogen bonds. This explains the
exceptionally high boiling points and melting points of compounds like water and
hydrogen fluoride. Hydrogen bonding plays an important role in biology; for
example, hydrogen bonds are responsible for holding nucleotide bases together
in and RNA.
3. Ion-dipole . The ions and the oppositely charged ends of the polar water
molecules overcome the attraction between ions themselves. Each ion becomes
separated and water molecules cluster around it.
4.
1. London dispersion forces, under the category of van der Waal forces: These are
the weakest of the intermolecular forces and exist between all types of molecules,
whether ionic or covalent—polar or nonpolar. The more electrons a molecule has,
the stronger the London dispersion forces are. For example, bromine has more
electrons than chlorine, so bromine will have stronger London dispersion forces
than chlorine, resulting in a higher boiling point for bromine, compared to
chlorine.. Also, the breaking of London dispersion forces doesn’t require that much
energy, which explains why nonpolar covalent compounds like methane oxygen,
and nitrogen—which only have London dispersion forces of attraction between the
molecules—freeze at very low temperatures.
The types of intermolecular forces in a liquid depend on the chemical
make up of the liquid itself. Strength of intermolecular force is related to the type of
intermolecular force, but it is also affected by the amount of kinetic energy in the
substance. The more kinetic energy, the weaker the intermolecular forces. Liquids
have
more
kinetic
energy than solids, so
the
intermolecular
forces between liquid
particles tend to be
weaker. Liquids do not have
a simple or regular structure, but many of their
properties can be explained qualitatively by viewing them at the particulate level.
Below are the properties of liquids and their intermolecular forces.
1. Surface tension allows needles and paper clips to float in water if placed carefully
on the surface. It also explains why drop of water are spherical in shaped. These
intermolecular forces tend to pull the molecules into the liquid and cause the surface
to tighten like an elastic film or “skin”. 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. The liquids
that have strong Intermolecular forces also have high surface tension
2. Capillary action is the tendency of a liquid to rise in narrow tubes or be drawn
into small openings such as those between grains of a rock. Capillary action, also
liquid to rise, is a result of intermolecular attraction between the liquid and solid
materials. Example of capillary actions.
There are two types of forces are involved in capillary action:
Cohesion is the intermolecular attraction between like molecules (the
liquid molecules).And Adhesion which is an attraction between unlike molecules
(such as those in water and in the particles that make up the glass tube).
3.Viscosity. The viscosity of liquid Depends on their intermolecular attraction. The
stronger the intermolecular force, the higher is the liquid’s viscosity. Example is oil
which has long-chained substances that has greater intermolecular forces because
there are more atoms that can attract one another, contributing to the substance’s
total attractive forces. Also with honey, a concentrated solution of sugar, is also highly
viscous because of the hydrogen bonding that forms as a result of the numerousOH groups of sugar molecule.
Substances with relatively strong intermolecular forces will have low vapor
pressure because the particles will have difficulty escaping as a gas.
Example:
1.Wate (H O),
2
(Hydrogen Bonding) has vapor pressure of 0.03 atm.
2.Ethyl Ether
(C H O), dipole-dipole & London Force ) has vapor pressure at 0.68
4 10
atm.
4. Boiling point. The boiling point of a liquid is the temperature at which its vapor
pressure is
equal to the external or atmospheric pressure .Increasing the
temperature of a liquid raises the kinetic energy of its molecules, until such point
where the energy of the particle movement exceeds the intermolecular forces that
hold them together.The greater intermolecular force, the higher the energy needed to
increase the kinetic energy of the molecules to break these forces.
5. Molar Heat of vaporization ( H
vap
) is the amount of heat required to vaporize one
mole of substance at its boiling point.T he application of heat disrupts the
intermolecular forces of attraction of the liquid molecules and allows them to
vaporize. Boiling point generally increases as molar heat of vaporization increases.
6. The
molecules.
H
vap
is also determined by the strength of intermolecular forces between
Let us continue on the properties of solids and their intermolecular forces. As
you should remember from the kinetic molecular theory, the molecules in solids are
not moving in the same manner as those in liquids or gases. Solid molecules simply
vibrate and rotate in place rather than move about. Solids are generally held together
by ionic or strong covalent bonding, and the attractive forces between the atoms,
ions, or molecules in solids are very strong. In fact, these forces are so strong that
particles in a solid are held in fixed positions and have very little freedom of
movement. Solids have definite shapes and definite volumes and are not
compressible to any extent.
There are two main categories of solids—crystalline solids and amorphous
solids. Crystalline solids are those in which the atoms, ions, or molecules that make
up the solid exist in a regular, well-defined arrangement. The smallest repeating
pattern of crystalline solids is known as the unit cell, and unit cells are like bricks
in a wall—they are all identical and repeating. The other main type of solids are called
the amorphous solids. Amorphous solids do not have much order in their
structures. Though their molecules are close together and have little freedom to
move, they are not arranged in a regular order as are those in crystalline solids.
Common examples of this type of solid are glass and plastics.
There are four types of crystalline solids:
Ionic solids—Made up of positive and negative ions and held together by electrostatic
attractions. They’re characterized by very high melting points and brittleness and are
poor conductors in the solid state. An example of an ionic solid is table salt, NaCl.
Molecular solids—Made up of atoms or molecules held together by London
dispersion forces, dipole-dipole forces, or hydrogen bonds. Characterized by low
melting points and flexibility and are poor conductors. An example of a molecular
solid is sucrose.
Covalent-network (also called atomic) solids—Made up of atoms connected by
covalent bonds; the intermolecular forces are covalent bonds as well. Characterized
as being very hard with very high melting points and being poor conductors.
Examples of this type of solid are diamond and graphite, and the fullerenes. As you
can see below, graphite has only 2-D hexagonal structure and therefore is not hard
like diamond. The sheets of graphite are held together by only weak London forces!