chapter [2] atomic structure and bonding
TRANSCRIPT
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.