chapter [2] atomic structure and bonding

LECTURE 2

IN MSE 300

ATOMIC STRUCTURE

SUBATOMIC PARTICLES

(Whitten et. al., 2007)

SUBATOMIC PARTICLES

Evidences

• Radioactivity (H. Becquerel, M. Curie, E. Rutherford)

• Cathode ray experiments (J.J. Thomson)

• Oil Drop experiment (R. Millikan)

• Canal Ray experiment

• Alpha particle experiment (E. Rutherford)

RADIOACTIVITY

• H. Becquerel, M. Curie, E. Rutherford

• Atoms can in fact break down

• Uranium, Polonium

• Radioactive elements can emit 3 kinds of radiation

Alpha () particles positive (+)

Beta () particles negative ()

Gamma () particles no detectable charge

CATHODE RAY EXPERIMENT

• J.J. Thomson

• Cathode rays () can be deflected by an Electric field

repelled from the negative plate and attracted to the positive plate

• Cathode rays () can be deflected by a Magnetic field

• Electrons have mass

• By balancing the effect of the applied magnetic and electric field, electron’s mass to charge ratio was computed

(Whitten, 2007)

OIL DROP EXPERIMENT

• Robert Millikan

• Charge-to-mass ratio of different sizes of negatively charged oil drops

• Established the charge on the electron

• Mass of an electron = 9.10938 x 10-28 g

• Charge of an electron = 1.602 x 10-19 C

(Whitten, 2007)

CANAL RAY EXPERIMENT

• Collision of cathode rays (electrons) and gas molecules strips electrons from the molecules

• The positively charge particles formed a canal through holes in the cathode ()

• Different gas molecules resulted to positive particles with different mass-to-charge ratio that are multiples of that derived from hydrogen

• Positive particle of hydrogen (proton) was the most fundamental

(Whitten, 2007)

-PARTICLE EXPERIMENT

• Ernest Rutherford

• Thin gold foil was bombarded with alpha particles (+)

most passed straight through

Some were deflected in large angles

Few were deflected backward

• Positive charge is concentrated in the center in a very small volume

(Whitten, 2007)

(Whitten, 2007)

THE ATOM

• Atomic number

Number of protons

• Atomic weight or atomic mass

Mass per atom or mass per mole of atoms

• Mass number

Number of protons + neutrons

• Charge

+ (cation)

(anion)

Neutral (free)

COMPLETE THE TABLE

Name Symbol No. of

p+

No. of

e-

No. of

n0

Mass

no.

Net

charge

14 28 0

8 10 16

10 20 2+

Oxygen 8 18

Na23

Name Symbol No. of

p+

No. of

e-

No. of

n0

Mass

no.

Net

charge

Sodium 11 11 12 23 0

Silicon 14 14 14 28 0

Oxygen 8 10 8 16 2-

Neon 10 8 10 20 2+

Oxygen 8 8 10 18 0

Na23

Si28

220Ne

O18

2O16

COMPLETE THE TABLE

ISOTOPES

• Atoms of the same element (same atomic number) having different atomic masses

ISOTOPES

• Atoms of the same element (same atomic number) having different atomic masses

ATOMIC MODELS

(Whitten et. al., 2007)

Photoelectric

Effect

Because of his explanation of the

photoelectric effect, Einstein received the

1921 Nobel Prize in physics.

When electromagnetic radiation of sufficient

energy (the energy must be equal or greater than the

amount needed to liberate the electron) strikes the

surface of metal inside an evacuated tube,

electrons are stripped off the metal to create

electric current.

Photoelectric

Effect

Because of his explanation of the

photoelectric effect, Einstein received the

1921 Nobel Prize in physics.

1 photon striking 1 electron

increase in intensity increase in number of photons

Thus, increasing the current

(Whitten, 2007)

BOHR ATOM

• Dot at the center represents nucleus

• radius n2 (1:4:9:16)

• Electronic energy is quantized

Table 5-4, p. 195

QUANTUM NUMBERS

• Principal (n) – main energy level

n = 1,2,3,4,…

• Angular momentum (l) – sublevel or subshell or specific shape of the atomic orbital

l = 0,1,2,3,…,(n-1)

• Magnetic (ml) – specific orbital within

ml = - l…,0,…+ l

• Spin (ms) – spin of the electron and the orientation of the magnetic filed produced

ms = +1/2, -1/2

Table 5-4, p. 195

QUANTUM NUMBERS

Table 5-4, p. 195

ELECTRON CONFIGURATION

• Ground vs excited state electron cofiguration

• Aufbau principle

• (n+ l) rule

• Pauli Exclusion Principle

• Hund’s Rule

p. 201

Fig. 5-30, p. 201

p. 224

Fig. 6-2, p. 225

Table 6-1, p. 225

Table 6-2, p. 228

Fig. 6-3, p. 228

p. 228

Fig. 6-4, p. 230

p. 230

p. 232

BONDING FORCE AND ENERGY

)()( rFrFF RAnet

RAnet

r

RAnet

EEE

drFFE

)(

BONDING FORCE AND ENERGY

)()(

0

00 rFrF

F

mequilibriuat

RA

net

0

)()(

)(

0

0

00

min,

net

rr

net

RAnet

r

RAnet

Fdr

dE

rErEE

drFFE

BONDING ENERGY VS TM

IONIC BONDING

• Metal + Non-metal (significant difference in EN)

• Ionization or transfer of electron

(+) cations Li+ Na+ Be2+ Mg2+ Al3+

() anions O2- S2- Cl- Br- I-

• Columbic attraction

• Repulsive Force

2

210

2

))((

r

A

r

qZqZkFF CA

r

eForr

BF RmR

BONDING FORCE

• Net force of attraction and repulsion

• Equilibrium bond length, r0, if Fnet = 0

mRCnet

RCnet

r

B

r

qZqZkFFF

er

qZqZkFFF

r

2

2

))((

))((

210

210

COULOMBIC FORCE

• Attraction between two oppositely charged species

0 = 8.85 x 10-12 F/m = 8.85 x 10-12 C/Vm

k0 = 9 x 109 Vm/C

Z = valence charge

q = electronic charge = 1.602 x 10-19 C

a = center-to-center distance

22

))(())((

4

1 21021

0 r

qZqZk

r

qZqZFC

COULOMBIC FORCE

Sample Problem

Compute the coulombic and repulsive force of attraction between Na+ and Cl- in NaCl.

(rNa+= 0.098 nm; rCl-= 0.181 nm)

22

))(())((

4

1 21021

0 r

qZqZk

r

qZqZFC

BONDING ENERGY

• Net energy of attraction and repulsion

• Equilibrium bond length, a0, if Fnet = 0

r

Der

qZqZkEEE RCnet

))(( 210

0

0

net

rr

net Fdr

dE

BONDING ENERGY

Sample Problem

The net potential energy between two adjacent ions, Enet, is sometimes represented by the expression:

Derive the expression for equilibrium inter-ionic spacing, r0, and bonding energy, E0, and in terms of the parameters C, D, and .

r

Der

CEEE RCnet

BONDING ENERGY

Sample Problem

The net potential energy between two adjacent ions, EN, may be represented by the equation below:

Calculate the bonding energy, E0, and equilibrium inter-ionic spacing, r0, in terms of the parameters A, B, and n.

nRCnetr

B

r

AEEE

COVALENT BONDING

• Sharing of electrons between adjacent atoms with relatively small or zero electronegativity difference

• Directional

• Valence electron

• Single, double, triple

• Bond Length

• Bond Energy

Fig. 7-3, p. 259

COVALENT BONDING

COVALENT BONDING

Methane Molecule Hydrogen gas

COVALENT BONDING

Bond Energies and Bond Length for Representative Covalent Bonds

Bond Bond

Energy,

Bond

Length,

Bond Bond

Energy,

Bond

Length,

kJ/mol nm kJ/mol nm

CC 370 0.154 CCl 340 0.18

C=C 680 0.13 OH 500 0.10

CC 340 0.12 OO 220 0.15

CH 435 0.11 OSi 375 0.16

CN 305 0.15 NH 430 0.10

CO 360 0.14 NO 250 0.12

C=O 535 0.12 FF 160 0.14

CF 450 0.14 HH 435 0.074

COVALENT BONDING

Ethylene

Polymerization of Polyethylene

ENERGY OF REACTION

Polymerization of Polyethylene

Bond Bond

Energy,

Bond

Length,

kJ/mol nm

CC 370 0.154

C=C 680 0.13

CH 435 0.11

METALLIC BONDING

• Primary bonding found in metals and its alloys

• Involves electron sharing

• Undirectional

• Sea of electrons, electron clouds, delocalized electrons

• Ions cores

METALLIC BONDING

• Free electrons shield the positively charge ion cores from mutually repulsive electrostatic forces

• Free electrons act as a glue to hold the ion cores together

METALLIC BONDING

• Bonding energy

E r

SECONDARY BONDING

• Van der Waals bonding

• Induced Dipole

• Permanent Dipole

• Hydrogen bonding

BONDING ENERGY

Sample Problem

A common way to describe the bonding energy curve for secondary bonding is the “6-12” potential,

For argon, KA=10.37x10-78 Jm6 and KR=16.16x10-135

Jm12, calculate the bond length (in nm) and bond energy per mol (kJ/mol) for argon.

126 r

K

r

KE RA

net

References:

[1] Callister, William D. Jr., Materials Science and

Engineering, 6th ed., John Wiley and Sons, Inc.,Singapore

(2009).

[2] Shackelford, James F., Introduction to Materials Science for

Engineers, Pearson Education Inc., Upper Saddle River, NJ

(2004).

[3] Van Vlack, Lawrence H., Materials Science for Engineers, 4th

ed., Addison-wesley Publishing Co., Inc., Philippines (1980).

[4] Whitten et. al., Chemistry, 8th edition. U.S.A., David

Harris, 2007.