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Chapter 11 : The States of Matter
Physics SF 017 Part III : Properties of Matter
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Chapter Outline :
11.1 Molecular Bonding
11.2 Solids, Liquids and Gases
11.3 Crystalline solid
11.4 Amorphous Solids and Polymers
11.5 Intermolecular Forces
11.6 Potential Energy between Molecules
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At the end of this topic, student should be able to :
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1. Explain molecular ionic, covalent, Van der Waals and
hydrogen bonds.
2. Distinguish between Solids, Liquids and Gases basedon arrangements of atoms and simple model of Kinetic
Theory.
3. Describe the properties ofCrystalline Solid by
referring to ionic crystals, covalent crystals andmetallic crystals
4. Describe the properties ofAmorphous and Polymers
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11.1 Molecular Bonding-- Matter is normally classified as being in one of 3 states :
Solid
Liquid
Gaseous
-- All matter consists of some distribution of atoms or molecul
-- The atoms in a solid are held by forces that are mainly
electrical, at specific positions with respect to one
another and vibrate about these equilibrium positions.
-- there are some simplified models / bonding mechanisms in
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-- 4 simplified bonding mechanisms in molecules :
Ionic Bonding
Covalent Bonding
Van der Waals Bonding
Hydrogen Bonding
(a) IonicBonding
-- occurs b
etween charged particles. ( between metal
atoms and non-metal atoms.)-- Metals usually have 1,2, @ 3 electrons in their
outermost shell.
-- Non-metals have 5,6 @ 7 electrons in their outer
shell. Atoms with outer shells that are only partlyfilled are unstable.
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-- To become stable:
the metal atom get rid of the electrons in its outer shelllost e- --forms a positively-charged ion.
the non-metal atom receive electrons from the metal
atom -- forms negatively-charged ion.
-- attractive between +ve & -ve charges( opposite
charges ) keeps the ions together.
Example 1:
Na Cl Cl-Na+
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(b) Covalent Bonding
-- occurs between two ( or more ) non-metal atoms.
-- Non-metals have 4 or more electrons in their outer
shells ( except Boron ).
-- energy to remove all the e- >> energy can gained by
making new bonds.
-- to overcome : the atoms involved donate 1 electron
each to share pair of electron. ---- allow each atomto have a full outer shell for part of the time.
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Example 2:
C H+ 4 CH H
H
H
-- the bonds/ forces between molecules are usually weak.
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(c) Van der Waals Bonding
-- relatively weak bonding between neighboringmolecules eitherdue to momentary dipoles or due
to electrostatic interactions among polar molecules.
-- 3 types of van der Waals forces :
(a) Dipole-dipole force(b) Dipole-induced force
(c) Dispersion force.
-- For 2 molecules that are some distance apart or
for atoms that do not form ionic @ covalent bonds,
they are attracted to each other by van der Waals
forces.
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(d) Hydrogen Bonding
-- occurs between hydrogen atoms covalently bonded
to nitrogen, oxygen or fluorine atoms is attracted to
an unshared electron pair of a similar highly
electronegative atoms in the same or adjacentmolecules.
-- relatively weak compared with other chemical
bonds, hydrogen bonding is the mechanism
responsible for the linking of biological moleculesand ol mers.
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11.2 Solids, Liquids and Gases
Solids
-- molecules are held rigidly in position with virtually
no freedom of motion.
-- have a definite volume and shape
-- virtually incompressible -- because of this tight pack
of particles.
-- vibrate about fixed positions
-- the density of the solid form is higher
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Liquids
-- molecules are close together but are not held so
rigidly in position can slide past one another freely .
-- has a definite volume ( molecules in a liquid do
not break away from the attractive forces ) but
assumes the shape of its container.-- can flow & can be poured.
-- more denser that gases under normal conditions.
-- only slightly compressible.
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-- The particles in gases are not neatly
arranged, -- don`t even touch each
other most of the time.lots of space in
between particles.
Gases
-- very free motion randomly.
-- lack of strong forces between molecules
allows a gas to expand to fill the volume of
its container.
-- have a very low densities under normal conditions (
large amount of empty space )
-- very compressible.
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11.3 Crystalline solid
Solids can be divided into 2 categories :
Crystalline
Amorphous
Crystalline solid (ex: ice) , possesses rigid and long-range order; its atoms, molecules, or ions occupy
specific positions.
Net attractive intermolecular forces are at theirmax.
The forces responsible for the stability of a crystal can
be ionic forces, covalent bonds, van der Waals forces,
hydrogen bonds or a combination of these forces.
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Unit cell the basic repeating structural unit of a crystalline
solid.
Any of the unit cells, when repeated in space in all 3
dimensions, forms the lattice structure characteristic of a
crystalline solid.
Every crystalline solid can be described in terms of1 of the
7 types of unit cells shown in Figure below.
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(a) Ionic Crystals
We can classify any crystal as one of 4 types : ionic,
covalent, molecular or metallic.
Lattic
e :Bond : Electric
attraction
example : Sodium chloride,
NaCl
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Propertie
s :
1. Hard & stable
2. High melting points indication of the strong
cohesive forces holding the ions together.
3. Do not conduct electricity because the ions are
fixed in position.
4. In molten state or dissolved in water, the ions are
free to move liquid is electrically conducting.
5. May be soluble in polar liquids such as water (
H2O ).
6. Brittle
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(b) Covalent Crystals
Lattic
e :
Bond : Shared
electrons
example : Diamond, C ; Graphite ;
Quartz ( SiO2 )
Properties :
1. Very Hard
2. High melting point3. Insoluble in nearly all liquids
4. Semiconductors ( except diamond which is an
insulator )
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(c) Metallic Crystals
example : All metallic elements ; such as
Na, Mg, Fe, CuLattic
e :
Bond : electron
gas
Properties :
1. Ductile
2. Metallic luster
3. High electrical and thermal conductivity.4. Semiconductors ( except diamond which is an
insulator )
5. Usually very dense
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(d) Molecular Crystals
example : Methane, CH4 ; sulfur
dioxide, SO2
Lattic
e :
Bond : Van der Waals
forces and/ or
Hydrogen bonding
Properties :
1. soft
2. Low melting and boiling points
3. Soluble in covalent liquids4. Electrical insulators
5. More easily broken apart than ionic & covalent
crystals.
6. Poor conductor of Heat.1 Nov 2002 Physics Dept. College Matriculation Johor ..21
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11.4 Amorphous Solids and Polymers
Amorphous
-- Lack a well-defined arrangement and long range
molecular order.
-- atom are arranged randomly.
-- example : glass, plastic, wax, sootProperties :
1. Hard but brittle ( easily broken )2. Electricity & Heat insulator
3. Do not have specific melting point
4. Do not have long-range repetitive internal
structures
5. Soften gradually when they are heated.
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Polymers
-- large molecules consisting ofrepeated chemical units (
`mers ` ) joined together usually in a line like beads on
a string.
-- ExAmpLe : Polypropylene
--CH2CHCH3|
CH2CHCH3|
CH2CHCH3|
CH2CHCH3|
CH2CH-- ..etcCH3|
Propylene is the monomer for polypropylene
CH2==CHCH3|
Propylene
-CH2CH-CH3|
Repeating unit in polypropylene
-(-CH2CH -)-nCH3|
Polypropylene
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2 types of polymers :
(a)Natural organic PolymersProtein, Natural
rubber ( latex ), wool
(b)Synthetic Organic polymersNylon, artificial
rubber.
Properties :
1. Good Insulator2. Rubbery, stiff, can be quite brittle
3. Do not have specific melting point because do not
have specific structural.
4. Soft but unyielding.
5. Only dissolved in organic liquids.
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Repulsive Force
Repulsive Force
r < r0
Attractive ForceAttractive Force
r > r0
r0 ( equilibrium separation )
11.5 Intermolecular Forces
The existence of 3 states or phases of matter is
due to a struggle between inter atomic (
intermolecular ) forces and the motion which
atoms ( molecules ) have because of their internal
energy.
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Repulsive Forces between 2 atoms
F repulsive = nr
A
where r = inter nuclear separation distance
A = parameter associated with the repulsive force
n = small integer
* F repulsive positive : in the r increasing direction
In addition to attractive inter atomic forces there must also
be inter atomic repulsion, otherwise matter would
collapse.
When the solid is compressed they repel each other ;
they attract when they are pulled fatherapart.
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Attrative Forces between 2 atoms
F attractive =2
2
r
eke
where k e = 8.99 x 109 N m2 C -2
= Madelung constant ; 1.7476
r = inter nuclear separation distancee = electron charge
* F attractive negative : in the r decreasing direction
Resultant Forces between 2 atoms
F resultant = F repulsive + F attractive
n
r
A
2
2
r
eke
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Graph Intermolecular force, F versus separation distance betwe
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At r = r0( equilibrium separation )
-- the attractive and repulsive forces just balance.|F repulsive | = | F attractive |-- the resultant inter atomic force = zero
At r < r0
-- if the atoms come closer than equilibrium, their
electron shells try to repel them thus creating a
very short-range & strong repulsive force.
|F repulsive | > | F attractive |-- resultant force F resultant: positive ( > 0 )
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At r > r0
-- at very large separation distances, the
dominant forces are attractive.| F repulsive | < | F attractive |-- F resultant : negative ( < 0 )
-- F attractive :long-range force
decrease slowly when r increase.
at infinite distance, the force zero.
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Relationship between Hooke`s Law and the FversusrGraph
The atoms are pulled apart very slightly; -- displaced a tiny distance from its
equilibrium position and the material
lengthens.
The intermolecular force curve is straightat and near equilibrium.
-- means the force is proportionalto the
displacement fromequilibrium.
Bonds between atoms in solids are liketiny Hooke`s Law spring provided they
are not extended too much. Whole
structure is not stretched too much
Hookes law is obeyed.
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W = Force x Distance
dW = - F dr
F =dr
dW
dr
dUF
dU = - F dr
U = - F dr
-ve : The force F between the molecules due to their interaction is =
and opposite to the force applied to move them.
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Graph Potential Energy between molecules, U versus separatio
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When very far apart, theirP.E. due to interaction = zero.
When they are moved towards each other theirP.E. falls because the
attraction between them.
The P.E. continues to fall until they reach the position where the overall
force changes from attraction to repulsion.
If they move closer still, the P.E. rises because work must done on the
system to push them together against the repulsion forces.
Th i i f th P E
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The minimum of the P.E. curve
occurs where the force changes from
attraction to repulsion where the
overall force is zero.
at r0 -- P.E. minimum
The force due to the interactionbetween the 2 molecules = - gradient
of the P.E. curve.
dr
dUF
At r0
, F=0, P.E. curve gradient = 0
At separation r > r0 , F 0
At separation r < r0 , F >0; P.E. curve
gradient < 0
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Using graph U vs r to explain : Thermal Expansion
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-- Solids expand when heated.
-- The atoms vibrate more & more as more & more energy is supplied.
-- The separation between any pair of adjacent atoms varies about the
equilibrium value as they vibrate.
-- At absolute zero ( T =0K) , the atoms do not vibrate so theirseparation isr0
-- At temperature T1, the atoms vibrate so that their separation varies from r1
to r1`. Because the P.E. curve is sharper at separation less than r0, r1 is
closer to r0 than r1`. So average separation, midway between r1 and r1` is
greater than r0
-- At increased temperature T2, the vibration increase so their separation
varies from r2 to r2`. The shape of the P.E. curve is such that the average
separation, midway between r2 and r2` is even greater.
-- for whole network of atoms, an overall expansion takes place.
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That `s all about Chapter 11 : The States ofMatter