chapter 11 properties of matter

7/27/2019 Chapter 11 Properties of Matter

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Chapter 11 : The States of Matter

Physics SF 017 Part III : Properties of Matter

1 Nov 2002 Physics Dept. College Matriculation Johor ..1


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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 :


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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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

chapter 11 properties of matter

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