Download Online Course Evaluation Chapters 15-20

Chapters 15-20
Online Course Evaluation
www.pa.uky.edu
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Chapter 15:14,18,20,22,23,26,50,62
Chapter 16:15,16,19,24,25,43,45,63
Chapter 17:12,34,35,36
Chapter 18:7,8,9,13,14,45,47
Chapter 19: 7,8,18,19,20,27,28,29,
30,31,34,38,40,45,46,53,56,63,65,66
• Chapter 20:10,11,16,18,19,23,24,25,30,
33,35,58,61,63
(Reduced to 68 from 95 problems)
Equations Associated with The Bohr Model
Line and Absorption Spectra
Electron’s angular momentum
L=Iω=mvrn=nh/2π, n=1,2,3
n is called quantum number of the orbit
hf=Eu- El
hc/λ=Eu - El
1/λ=(1/hc)Eu- El
Radius of a circular orbit
rn=n2h2/4π2mkZe2=(n2/Z)r1
where r1=h2/4π2mke2=5.29x10-11 m (n=1)
r1 is called Bohr radius, the smallest orbit in H
Total energy for an electron in the nth orbit:
En=(-2π2Z2e4mk2/h2)(1/n2)=(Z2/n2)E1
where E1=-2π2Z2e4mk2/h2 =-13.6 eV (n=1)
E1 is called Ground State of the hydrogen
1/λ=(2π2Z2e4mk2/ch3)(1/nl2-1/nu2)
Both orbits and energies depend on n, the quantum number
Question: With increasing quantum number, the
energy difference between adjacent energy
levels
(a) decreases
(b) remains the same
(c) increases
(d) sometimes decreases and sometimes
increases
Answer: a
Question: An atom emits a photon when one of its
electrons
(a) collides with another of its electrons
(b) is removed from the atom
(c) undergoes a transition to a quantum state of
lower energy
(d) undergoes a transition to a quantum state of
higher energy
Answer: c
Question: The bright-line spectrum produced by
the excited atoms of an element contains
wavelength that
(a) are the same for all elements
(b) are characteristic of the particular element
(c) are evenly distributed throughout the entire
visible spectrum
(d) are different from the wavelength in its darkline spectrum
¾ The presence of definite energy levels in an atom is true for all
atoms. Quantization is characteristic of many quantities in
nature
¾ Bohr’s theory worked well for hydrogen and for one-electron
ions. But it did not prove as successful for multielectrons.
¾ It is quantum mechanics that finally solved the problems
Answer: b
Early Quantum Theory
¾ Quantum energy: E=hf
¾ Photoelectric effect: hf=KEmax+Wo
¾ De Broglie wavelength: λ=h/mv
¾ Bohr theory: L=mvr=nh/2π
En=E1/n2 where E1=-13.6 eV
¾ Wave-particle duality
Limitations of the Bohr Theory
¾Unable to predict the line spectra for more
complex atoms
¾Unable to predict the brightness of spectral
lines of hydrogen
¾Unable to explain the fine structure
¾Unable to explain bonding of atoms in
molecules, solids and liquids
¾Unable to really resolve the wave-particle
duality
Quantum Mechanics
¾It solves all these problems and has
explained a wide range of physical
phenomena.
¾It works on all scales of size. Classical
physics is an approximation of quantum
physics
¾It uses an abstract mathematical formulation
dealing with probabilities
Chapter 29 Nuclear Physics
Nuclear Structure
Binding Energy
Radioactivity (α,β, and γ Decay)
A tiny positively charge object:
Nucleus
¾The elements exist by virtue of the ability of
nuclei to hold multiple electric charges
¾The energy involved in nearly all natural
processes has its ultimate origin in nuclear
reactions and transformation
Atomic Nuclei consist of Protons and
Neutrons
Proton
Positive charge, e=1.6x10-19 C
mproton=1.673x10-27 kg
Neutron
Uncharged
mneutron=1.675x10-27 kg
Except in H, the number of neutrons equals
or,more often, exceeds the number of
protons.
Atomic number Z:
The number of protons (or electrons)
Atomic mass number A
The number of protons and neutrons
Atomic mass unit
1u=1.66x10-27 kg
me=0.000549u,mp=1.007277u, mn=1.007825u
Isotopes
Nuclei that contain the same number of protons and
different numbers of neutrons
Nuclear radius
r≈(1.2x10-15m)(A1/3)
Binding
Energy
Nucleus
(smaller mass)
Separated nucleons
(greater mass)
Binding Energy
¾ Atomic nuclei always have less mass than the
combined masses of their separated particles.
¾ The “missing” mass of a nucleus is called its
binding energy, the energy needed to break it up
into separate protons and neutrons.
¾ Average binding energy per nucleon equals total
binding energy divided by A
Question: Relative to the sum of the masses
of its constituent nucleons, the mass of a
nucleus is
a. greater
b. the same
c. smaller
d. sometimes greater and sometimes smaller
Answer: c
Region of greatest stability
The higher the binding energy per nucleon, the more stable the nucleus.
Nuclei of intermediate size (A=50-80) are the most stable.
Question: The element whose nuclei contains
the most tightly bound nucleons is
a. Helium
b. Carbon
c. Iron
d. Uranium
Answer: c
What holds nuclei together?
Strong nuclear force between nucleons, the third
fundamental force.
¾ The strongest of all the fundamental forces by far.
¾ Short range, effective only over a few nucleon
diameters, ~10-15 m
The short range of nuclear forces is responsible
for the restricted number of stable elements
The larger a nucleus, the stronger the electric
repulsive forces that act on each of its proton, the
attractive strong nuclear forces on each nucleon
cannot increase indefinitely because only a limited
number of other nucleons are close enough to
interact with it.
An unstable nucleus comes apart, and results in
Radioactivity
Strong nuclear force
(Short range, 10-15 m)
Electric force
F21 +Q2
+Q1 F
12
r12
F12 = k
Q1Q2
r122
Electric force
There are three radioactive decay mechanisms
α-decay: emission of an a-particle (He-nucleus)
β-decay: emission of an electron
γ-decay: emission of a high energy photon
α
γ
β
Why α decay?
α decay occurs because the short range
strong nuclear force is unable to hold very
large nuclei together
Why α particle?
α particle is very strongly bond, the mass is
significantly less than that of four separate
nucleons
Weak Nucleus Force
In β decay, it is the weak nucleus force that
plays the crucial role: the neutrino interacts
with the matter via the weak force. It is
effective over a range of 10-17 m
The electron are created within the nucleus
itself:
n p + e-. It is Not an orbital electron
The mass and proton numbers do not change,
the daughter nucleus is simply the parent nucleus with less energy.
Parent nucleus and
daughter nucleus are
different
Parent nucleus and
daughter nucleus are
the same
Parent nucleus and
daughter nucleus are
different