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Chem 1

2nd Sem 2015-2016

Lecture 13

FCariño

Metallic bonding

• Normally, outer electrons inhabit energy level

called valence band, or "ground" state.

• on o energy can ra se ou er e ec rons ou

of valence band and into "conduction" band.

• In conduction band electrons free to move about

within crystal structure of metal. Application of

electric potential will influence them to move in

one particular direction.

http://education.jlab.org/qa/current_02.html

Metallic bonding

• Valence band relatively close to conduction

band - very little energy required for e-s to

 jump from valence state into conduction

band.

• Metal atoms have large population of free

e-s in conduction band all the time.

• application of electricity e-s move current

flow

• relatively low (though not zero) resistance.

http://education.jlab.org/qa/current_02.html

Electrical conduction

Conduction band

Band Gap

Valence band

Metals   Insulators

Semiconductors

http://education.jlab.org/qa/

current_02.html

http://nobelprize.org/educational

 /physics/semiconductors/6.html

Semiconductors

• Electrical conductivity can be increased by

“doping”

• Deliberately add impurity or contaminant to pure

substance

• n-type and p-type

p‐type,

 n‐type

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To continue…

Graham’s law of  effusion• The rates of diffusion of a gas is

inversely proportional to the square

roots of their molecular masses or

• Light gases move faster than

heavier ones

11

2

2

1

M

M

rate

rate

  

  2

 Avogadro’s law

• At constant pressure and temperature, there is

a direct relationship between the volume and

number of moles for an ideal gas.

• At constant temperature and pressure, volume is

rec y propor ona o e num er o moes o

gas

• One mole of a gas at STP (1 atm, 0oC) occupies avolume of 22.4 L.

• One mole of a gas contains 6.02 x 1023 molecules.

Sample problem

A volume of gas equal to 25 L was

collected at 250C and 1.00 atm

 pressure. What would be the

volume of the gas if it were

collected at 1000C and 0.85

atm pressure?

Sample problem

A volume of gas equal to 25 L was collected at

250C and 1.00 atm pressure. What would be

the volume of the gas if it were collected at

1000C and 0.85 atm pressure?

Given:

P1 = 1atm T1= 25oC

P2 = 0.85 T2=100oC

V1 = 25L n= constant

Sample problem

A volume of gas equal to 25 L was collected at 250C

and 1.00 atm pressure. What would be the volume

of the gas if it were collected at 1000C and 0.85

atm pressure?

Given:

P1= 1atm T1=25oC = 298o

P2 = 0.85 atm T2=100oC = 373oK

V1 = 25L n = constant

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Sample problemGiven:

P1 = 1 atm T1= 25oC = 298oK

P2 = 0.85 atm T2=100oC = 373oK

V1 = 25L n = constant

nRT2

22

nRT

VP

T

VP

2

22

1

11

nRT1

11

Sample problemGiven:

P1 = 1atm T1=25o

C = 298o

KP2 = 0.85 atm T2=100

oC = 373oK

V1 = 25L n = constant

2

22

1

11

TT   122211

  TVPTVP  

12

2112

TP

TVPV     L8.36

)K

)K

o

o

298(0.85atm)( 

 )(373(1atm)(25L

Sample problemGiven:

P1 = 1atm T1= 25oC = 298oK

P2 = 0.85 T2=100oC = 373oK

V1 = 25L n = constant

22

2112

TPV  

)K

)KV

2   o

o

373(0.85atm)( 

 )(298(1atm)(25L

Li uids

Fixed volume, variable shape

Liquids• Gases condense into liquids

• Increase- pressure on gas push molecules

togetherreduce temperature gas

condenses

• Molecules experience short range and weak

attractive forces (van der Waal’s attractive

forces)

• Particles far enough from each other allow

translational motion, slide past each other,

but movement more restricted than gas.

Intermolecular Forces

Interlude

(Interparticle forces) van der Waal’s

24 

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Surface tension

• Energy or work required to

increase surface area of liquids by

unit amount

• Occurs because of intermolecular

forces of attraction

Surface tension

• Attractive forces pull surfacemolecules towards interior and

compress molecules closer to each

other shrinkin surface area. 

• spherical droplets with “tight skin”

• stronger intermolecular forces of

attraction more energy required to

increase surface area higher surface

tension

Surface tensionSurface tension

39  

Pictures from:  A .  fotolia.com; B. rduauto.com; C. connectedwaters.unsw.edu.au ; D. discovermagazine.com; E. 

apparatus‐boschus.deviantart.com; F. www.123rf.com

E

D

A

mercury

B C

F

water

 Vapor pressure,

 evaporation

• Evaporation –surface phenomenon;

molecules of liquid enter vapor phase

• Occurs because attractive forces at

surface are weaker than those in bulk of

qu some mo ecu es escape n o gas

phase

• Pressure exerted by molecules that

escape into gas phase = vapor pressure

• Volatile – high vapor pressure

• Non-volatile – low vapor pressure

Boiling point

• Temperature at which vapor pressure =atmospheric pressure

• Normal boiling point – defined as boilingtemperature of liquid at 1 atm (101 kPa)

• lower atmospheric pressures: boiling point

decreases because less energy required tocounter atmospheric pressure

• Cooking at high elevations take much longerbecause water boils at lower temperature

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Images from: unit5.org; library.thinkquest.org

T at which vp =atm pressure

boiling point

Effects of non-

volatile solute on

vapor pressure