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• Rutherford’s gold foil experiment tells us that all atoms have a nucleus– Contains nucleons, protons and neutrons,
and always has a + charge as a whole– Extremely dense – Electrons are outside of it
Background Information
2
There’s More?
• Actually over 200 different particles in atoms, not just the 3
• The theory of Quantum Chromodynamics (QCD) says that some of these particles contribute to holding the nucleus together
3
Some Examples• Quark - a single proton is made up of
3 quarks• Pi meson (pion) - exchanged between
proton and neutron• Nu meson• Neutrino• Leptons, etc.
4
• Smashing atoms using particle accelerator, a device that uses:• 1. electric fields to
propel electrically charged particles to high speeds
• 2. magnetic fields to contain them
How Do We Know?
5
• Use of a bubble chamber (superheated liquid container) with accelerator – Charged particles pass
through and leave trails of bubbles
– Form helical shapes, due to a magnetic field applied to the chamber
– Analyze shapes to find the mass and charge of the particle
How do we know?
6
CERN
• On the Franco-Swiss border near Geneva
• "Conseil Européen pour la Recherche Nucléaire“ (European Council for Nuclear Research)
• 1952 • Established a world-class fundamental
physics research organization in Europe with a large Hadron Collider
• CERN Video 7
Atoms Have a Nucleus • 2 questions associated with an atom that
has a nucleus– 1) How does the nucleus stay together when
the protons repel each other? – 2) How do the negative electrons stay out of
the nucleus if they are attracted to the + protons in the nucleus?
8
Electromagnetic Force• Results from the
repulsion of like charges and the attraction of opposites
• Holds the electrons around the nucleus
-
+
+
+
--
Particles with the same charge move
apart and the particles with
different charges move together.
Why are neutrons not pictured above?
9
Strong Force• Force that holds the
nucleus together• Counteracts the
electromagnetic force’s repulsion (+-+)
• Only strong if the protons and neutrons are close!
• Large nuclei have lots of repulsion compared to strong forces
++
++
Notice how the electromagnetic force
causes the protons to repel each other but, the strong force holds them together.
Would an atom have a nucleus if the strong force did not exist?
10
Nuclear Forces
• Nuclear forces like the strong force that holds the nucleus TOGETHER are NOT
- gravitational in nature- electrical in nature
11
Isotopes• Isotopes are atoms of the same element
that have different numbers of neutrons (therefore, different mass #s)
• Hydrogen-1 Hydrogen-2 Hydrogen-3 1 2 3 H H H 1 1 1• Some isotopes are stable, some are not• Those that aren’t stable are radioactive
12
Importance of Neutrons-Reference
• All atoms > 1 proton have neutrons • As proton # increases, so does neutron
#NUCLEUS # OF PROTONS # OF NEUTRONS
12 C 6
6 6
56 Fe 36
36 26
207 Pb 82
82 125
14
Importance of Neutrons-Reference
• Neutron to proton ratio is related to the stability of the nucleus
• The greater the proton #, the larger the repulsion and higher ratio of neutrons needed STABLE NUCLEUS # OF NEUTRONS # OF PROTONS N:P RATIO
12 C 6
6 6 6÷6 = 11N:1P
56 Fe26
30 26 30÷26 = 1.151.15N:1P
207 Pb 82
126 82 126÷82 =1.541.54N:1P
15
General Rules of Stable Atom Size-Reference
Atom Size Example Stable Ratio of N:P
< 20 protons(Small)
He-4 2P: 2N1:1 ratio
21-55 protons(Medium)
Br-79 44N:35P1.3:1 ratio
> 55 protons(Large)
Au-197 118N:79P1.5:1 ratio
16
• This graph shows stable and unstable isotopes• Stable atoms have neutrons:proton ratios
that place them in the belt in the graph • In general, the more protons an atom has,
the more neutrons it needs to be stable• Note axes!
Importance of Neutrons
17
• Note most stable isotopes are blue dots• Neon? End of blue dots?
Importance of Neutrons-Reference
18
• There’s a limit on the number of protons in a stable nucleus no matter what the n:p ratio is:– The maximum number of protons in a stable
nucleus is 83!– More than 83 protons in the nucleus = unstable
and radioactive no matter what• Sea of Instability video 14 min
Importance of Neutrons
19
Review • Number your paper from 1-5 and answer
the following questions. Two will be cumulative review!
• 1. Which of these is the correct symbol for Chlorine-35?
• a. 35 Cl 17
• b. 17 Cl 37
• c. 17 Cl 35
20
Review
• A• 2. A typical nitrogen atom has 7
protons and 7 neutrons. What’s the actual mass of a typical nitrogen atom?
• a. 1.67 x10-24 g• b. 1.17 x10-23 g • c. 2.24 x10-23 g• d. 6.02x1023 g
21
Review
• A• 3. Which of these is true
• a. any atom can be stable if it has enough protons
• b. atoms below atomic number 83 are all unstable
• c. atoms with enough protons to balance the repulsive force of the electrons are stable
• d. the larger the atoms is, the more neutrons it needs to be stable
22
Review
• D• 4. Strong forces
• a. help overcome the negative charges of the electrons
• b. help overcome the repulsion of the neutrons
• c. help overcome the repulsion of the protons
• d. help overcome the attraction of the protons and electrons
23
Review
• C• 5. Which of these is false?
• a. protons repel protons• b. protons attract neutrons• c. protons attract electrons• d. neutrons don’t repel anything
because they have no charge
24
Nuclear Symbols-Reference• Nuclear symbols are a way to write
atoms using the mass number and atomic number
• Format:
• Which of these numbers can change and still have the element be the same?
• Note! The element symbol tells you the atomic #, so sometimes this nuclear symbol is written without it: 12 C
26
Let’s Do It!!!
• Read over the left side of the Nuclear Symbols Review
• Get with a partner and complete the right side 10 min
27
• Radiation (radioactive decay)- release of particles and/or energy from an unstable nucleus
• Two kinds: natural or artificial – Natural radiation - nuclear changes that occur
in nature, not caused by humans
Radioactivity
28
3 Main Types of Natural Radioactive Decay-
ReferenceTYPE SYMBOL COMPOSITION STOPPED BYALPHA α or 4
He 2
2 p+
2 nOPAPER
BETA β or 0 e -1
1e- ALUMINUM
GAMMA ϒ Energy (no mass) LEAD
29
Alpha Radiation (Decay)
• Alpha particle consists of 2 protons and 2 neutrons • It’s essentially a He-4 nucleus (no
electrons)• 4 He 2
• Released when too many protons in the nucleus
• Atom changes in identity and mass • atomic # decreases by 2 (lose 2 p)• mass # decreases by 4 (2 p + 2 n)
• Alpha decay and Plutonium 30
Beta Radiation (Decay)
• Beta particle has the same mass and charge as an electron BUT released from nucleus – Released when n:p ratio is too high for size
(too many neutrons)
– O e -1
34
-n
Beta Radiation• Neutron can
change into a proton(+) and an electron(-)
• n p + e-• The electron is the
beta particle
+
Notice how the original particle changes to
something new.
36
• n p + e- • Atom changes in identity because new
proton increases atomic # by 1 • -Mass # stays same• More penetrating (higher velocity) than
alpha radiation so more dangerous
Beta Radiation
37
Gamma Radiation
• Just energy so no mass and most penetrating and dangerous of the 3 types
• Form of electromagnetic radiation like X-rays or light
• Causes no change in atom’s identity or mass
• Animation
40
Positron Emission
• Two other, more complicated forms of radioactive decay– positron – electron capture
• Positrons have same mass as an electron, but opposite charge - released from nucleus
• Proton changes to neutron when positron is released - not sure how
• Atom changes in identity only (atomic number decreases by 1 due to loss or proton) - mass stays the same
43
Electron Capture
• Sometimes the nucleus will capture an electron that gets too close to it
• This process is more rare, but it can occur - gamma radiation is always released
• Atom changes in identity only (atomic number decreases by 1) - mass stays the same
46
Nuclear Radiation Equations-Reference
• Write a chemical equation so on the left of the arrow is the starting atom in nuclear notation– Think of the arrow as an equal sign– The arrow means “produces”
• On the right is the particle + resulting atom
• Simple math makes it easy to solve• 238 = ? + 4•
92 = ? + 2
?49
Nuclear Radiation Equations-Reference
• Write a chemical equation so on the left of the arrow is the starting atom in nuclear notation– Think of the arrow as an equal sign– The arrow means “produces”
• On the right is the particle + resulting atom
• Simple math makes it easy to solve• 238 = 234 + 4•
92 = 90 + 2
50
Let’s Do It!!!Nuclear Equations video 7
min 214 0
82Pb ---------> __?__+ -1 e
51
• Number your paper from 1-5 and answer the following questions. Two will be cumulative review!
• 1. Atoms with the same atomic number but different mass numbers are
• a. different elements• b. ions• c. isotopes of the same element• d. isotopes of different elements
ReviewRadioactive Decay Video
8min
55
Review
• C• 2. Which of these has a 1:1 ratio of
neutrons to protons?• a. 34 Cl 17
• b. 17 Cl 37
• c. 35 Cl 17 56
Review
• A• 3. Naturally radioactive elements
• a. have unstable nuclei• b. give off alpha, beta, or gamma rays• c. can decay into another element• d. all of the above
57
Review
• D• 4.An alpha particle
• a. has a negative charge• b. can penetrate a sheet of aluminum• c. is identical to a helium nucleus• d. all of the above
58
Review• C• 5. Finish the equation: 222 4
86Rn ---------> __?__ + 2He
• a. 226 Cl 88
• b. 218 Po 84
• c. 218 Ra 88
59
• If the nucleus is STILL unstable, it will continue to decay further– This is one reason why radioactive material
can remain dangerous for long times– The other is that radioactive material doesn’t
all decay at once• Each radioactive element decays at
different rates, some very quickly, and some very slowly
Stability
61
Half-Life• Half-life (t1/2)- the time it takes for half the
mass of a radioactive sample to decay– Different for each radioactive isotope, not
affected by external conditions (T, P, etc.)– Range from fractions of seconds to billions of
years
62
• If you start with 10.0 g of Uranium, after 4.5 x 109 years (4.5 billion), you will have 5.00 g left
Half-life-Reference
𝐔❑𝟐𝟑𝟖𝟗𝟐 𝟒 .𝟓𝒙 𝟏𝟎𝟗𝒚𝒓𝒔 .
→
𝐓𝐡+ 𝜶❑
𝟒𝟐
❑
𝟐𝟑𝟒𝟗𝟎
63
Half-Life-Reference
• The half life of polonium-210 is 138 days• How many days are required for 7/8 of a
given amount of Po-210 to decay?• 3 half lives = 414 days where 1/8 is left
and 7/8 is decayed
138 days
66
• The half life of polonium-210 is 138 days
• What was the original mass of a sample of Po-210 if 0.250 g remains after 414 days?
• 414 days = 3 half-lives• The original mass was 2.000 g
Half-Life-Reference
0.250 g2.000 g 1.000 g 0.500 g
67
• The half life of polonium-210 is 138 days
• How much of a given amount of Po-210 remains after 552 days?
Let’s Do It!!!
68
• The half life of polonium-210 is 138 days
• How much of a given amount of Po-210 remains after 552 days?
• 552 days = 4 half-lives• 1/16 remains
Let’s Do It!!!
1/1669
Radioactive Isotopes in Medicine
• Some radioactive isotopes have extremely important uses in medicine
• Can be used to detect certain types of tumors
• Technetium-99m is an ideal isotope for scanning organs because it has a short half-life and is a pure gamma emitter
70
• Radioisotopes used in medicine have pros and cons
• Positives– Generate extremely accurate maps of
internal organs– Most have short half-lives and decay quickly
• Negatives:– Exposes patient to high levels of gamma
radiation (ypical dose = 500 chest X-rays)– Family members of patient also at risk of
exposure
Pros vs. Cons
72
• Suppose 80.0 mg of Tc-99m were prepared this morning and shipped to St. Anthony’s hospital. How many milligrams would remain after 24 hours?– 1 half-life = 6 hours– 24 hours = 4 half lives
6hrs 12hrs 18hrs 24hrs80.0mg 40.0mg 20.0mg 10.0mg 5.0mg
It would obviously be cost effective to use this isotope quickly
Sample problem
73
ReviewHalf-Life video 7min
• Number your paper from 1-5 and answer the following questions. Two will be cumulative review!
• 1. How many atoms of the isotope 14C are in a mole?
• a. 1• b. 14• c. 6• d. 6.02 X1023
74
Review • D• 2. Which of these is an alpha particle?
• a. 34 Cl 17
• b. 37 He 17
• c. 4 He 2
• d. 2 A -1
75
Review• C• 3. If you had 10 grams of each of the
following isotopes, which would still be highly radioactive after one million years?
• a. 90Sr b. 238U• c. 222Rn d. 218Po
76
Review
• B• 4. An isotope’s half-life
• a. is measured in grams • b. can be changed by chemical reactions• c. is usually greater than 1000 years• d. is the time required for half the mass
to decay into another element
77
Review• D• 5. If I have 8 grams of Rn-222 and 24
grams of Po-18, which sample will have more radioative material left in 12 days?
• a. Rn-222 b. Po-18 c. Both the same
78
Review
• A• Rn-222 will have 1 gram• 8421 with a half-life every 4 days,
or 3 half-lives in 12 days• Po-218 will have 1.5 grams• 2412631.5 with a half-life everyt 3
days, or 4 half-lives in 12 days
79
Natural Decay
• Uranium spontaneously decays on it’s own because it’s unstable
• 238 234 4
92 U 90 Th + 2He
80
Artificial Decay• Bombardment of a stable isotope to
force it to decay:• 14 4 1
• 7N + 2H 1p + ?
nuclear “bullet”• This is an example of the first ever done
– “Bullets” are + charged, and repelled by the huge + nucleus they are bombarding
– They must be accelerated to very high speeds by a particle accelerator to overcome repulsion and collide
81
Artificial Decay• Bombardment of a stable isotope to
force it to decay:• 14 4 1 17
• 7N + 2H 1p + 8 O
nuclear Hydrogen “bullet” atom• First ever done by Rutherford
– “Bullets” are + charged, and repelled by the huge + nucleus they are bombarding
– Accelerated to very high speeds by a particle accelerator like CERN has to force collision
82
Fission
• Nuclear fission - heavy nuclei are bombarded with neutrons, become highly unstable, and split– The gain in stability
releases lots of energy mostly heat
– Only certain isotopes of uranium and plutonium will undergo fission
83
Fission-Reference
1 235 142 91 1
0 n + 92U 56Ba + 36Kr + 3 0n + E• Mass of particles produced (234amu) is
slightly less than the mass of the reactants (236amu)—mass defect!
• This mass is converted into huge amounts of energy
• E = mc2
84
E = mc2
• Albert Einstein proposed that mass and energy were related in his special theory of relativity – If a substance gains mass, it gains energy– If a substance loses mass it loses energy
• Ex one gram of mass is converted to about 100 trillion joules of energy
•
86
Fission• Note that there are 3 neutrons produced
in the reaction• Atoms are mostly empty space, so
fission won’t continue naturally • Critical mass- minimum mass of
fissionable material required for a chain reaction
87
Fission-Reference• Controlled fission chain reactions used
to produce energy– Used in atomic bombs & nuclear reactors• Nuclear Fission
•
88
Fossil FuelsEasy AccessEasy to work
withAir PollutionOil SpillsNon-renewable
Nuclear FissionMore
energy/reactant (cheaper)
RadioactiveAccidents can be
catastrophic (Chernobyl)
89
• Same Substance Decays Different Ways-Reference
235 1 93 140 1 U + n Kr + Ba + 3 n +
ENERGY 92 0 36 56 0______________________________________ 235 1 144 90 1 U + n Xe + Sr + 2 n +
ENERGY 92 0 54 38 0______________________________________ 235 1 95 138 1 U + n Kr + Ba + 3 n +
ENERGY 92 0 36 56 0
90
Fusion
• 2 small nuclei fuse together to form one larger, more stable nucleus of intermediate size
• The increase in stability releases a large quantity of energy 91
• Essentially, hydrogen atoms are fused together to make helium atoms
• Used in hydrogen bombs and provides energy in stars like our sun
• Mass is converted into energy by the Einstein equation - mass of products is less than the mass of the reactants
Fusion
92
Our Sun
• As the Sun ages, the hydrogen nuclei are used up as they are fused into helium
• It’s a giant fusion reactor • It is estimated that the Sun has enough
hydrogen to keep this reaction going for another 5 billion years
93
FusionMore energy/reactantMore reactantsDifficult to controlDifficult to initiate without
super high temps (cold fusion not possible)
Less Radioactive
FissionRadioactiveAccidentsMore technologyEasy to initiate
with just neutrons
Fission vs. Fusion
94
Review Fission vs. Fusion video
7min• Number your paper from 1-5 and
answer the following questions. Two will be cumulative review!
• 1. Which of these is the correct specific heat for water ?• a. 1 cal/g °C • b. 0.897 J/g °C • c. 1 J/g °C • d. 4.184 cal/g °C
95
Review
• A• 2. An isotope’s half-life
• a. is measured in time • b. can be changed by chemical reactions• c. is usually greater than 1000 years• d. is half the time required for the mass
to decay into another element
96
Review
• C• 3. Where is this picture showing?
• a. Fission• b. Electron capture• c. Fusion• d. The Billiard Ball model of atomic
structure
97
Review
• A• 4. Where would you find this nuclear
reaction occurring? • a. the sun• b. a hydrogen bomb• c. your body• d. a nuclear reactor
98
Review
• D• 5. The minimum mass of fissionable
material required for a chain reaction is called
• a. nuclear mission • b. critical mass• c. half-life• d. theory of relativity
99
Still want to know more about radiation?
• Radioactive Teddybear Zombies
101
Atoms Have a Nucleus • Recall these 2 questions associated with
an atom that has a nucleus– 1) How does the nucleus stay together when
the protons repel each other? – 2) How do the negative electrons stay out of
the nucleus if they are attracted to the + protons there?
102
Why Doesn’t the Atom Collapse?
• It should because of the electrical attraction between the positive nucleus and the negative electrons, but it doesn’t
103
Outdated Explanation
• Solar System Model: electrons travel around the nucleus like planets around the sun, relying on gravity, so the electrons stay away from the nucleus like the planets stay away from the sun
• It was known this model had flaws and will not work with matter that has electric charges (planets are neutral)
104
Niels Bohr (1885 – 1962)
In 1913, proposed the Bohr Model of the atom- electrons travel at definite speeds around the nucleus of an atom in definite paths called orbits Electrons can jump from a path in
one level to a path in another level (depending on their energy)
How did he find this? Well, we need to talk about light
105
LIGHT
• Properties of light: – Electromagnetic radiation
spectrum– Can be produced in chemical
reactions– Can change matter– Constant velocity (symbol is c)
c = 3.00 X 108 m/sec – Can be reflected and refracted
(bent)– Responsible for color
106
• It takes approximately 8.3 minutes for light from our sun to reach Earth. How far away is the sun in miles?
? miles =
8.3 min in
ft
12
1*
min1
sec60*
m
cm
1
100*
ft
mile
5280
1*
sec1
10*00.3*
8m
= 93,000,000 miles
LIGHT-Reference
cm
inch
54.2
1*
107
Light Models
• There are 2 models that can explain light– 1. Wave model– 2. Particle model
• Neither theory is better than the other
108
• Light is a wave in which each has a– Wavelength (l)-
distance per cycle (m/cycle) between corresponding points on adjacent waves
– Frequency (v)- the number of waves passing a given point in a given time in cycles per second= cycles/sec (or Hz)
1. Wave Description of Light
109
Wave Description of Light• We can relate frequency and wavelength
of a wave to the speed of light as c = l v– c = 3.0 x 108 m/s : speed of light in a vacuum– Rearrange equation so that l = c/v – When frequency goes up, wavelength goes
down and vice versa (inversely proportional)
110
Sample Problem #1-Reference
• What is the frequency of light if the wavelength is 6.0 x 10 -7m/cycle?
l = 6.0 x 10 -7m/cycle• c = 3.0 x 108 m/s • c = l v so divide each side by l• v = c/ l • So v = 3.0 x 108 m x 1 cycle = sec 6.0 x 10 -7m v= 5.0 X 1014 cycles or Hz sec
111
Sample Problem #2-Reference
• Look at light wave (b). How many total waves are there? 3
• If the wavelength is 5 x10-7 m/cycle, what’s the frequency of this wave?
• v = c/ l so 3.0 x 08 meters x 1 cycle =
sec 5 x10-7 m
v = 6 x 1014 Hz = 6 x 1014 cycles sec
112
Let’s Do It!!!
• What is the wavelength of light if its frequency is 5.0 x 10 14Hz (cycles/sec)?
113
Let’s Do It!!!
• What is the wavelength of light if its frequency is 5.0 x 10 14 cycles/sec (Hz)?
• v = 5.0 x 10 14 cycles/ sec or Hz• c= 3.0 x 108 m/s • c = l v so divide each side by v = l c/v = l 3.0 x 108 m x sec = sec 5.0 x 10 14 cycles =l 6.0 x 10-7 m/cycle
114
2. Particle Description of Light
• Energy also exists as particles, called quanta or photons, which are bundles of energy with no measurable mass
115
The Modern View of Light
• Put forth by Einstein– Light has a dual nature– Light may behave as a wave– Light may behave as a stream of particles
called quanta or photons• Most scientists consider light to be
waves made up of particles
116
• An equation ties these 2 theories together:
• Photon E = (Planck’s constant) (frequency)
• E = h • n – h = Plank’s constant = 6.6 X 10-34 J. sec/cycle
or 6.6 X 10-27 erg . sec/cycle (1 erg = 1 x 10-7 J)– and n = frequency of wave
The Modern View of Light
117
• E = h • n – E and n are directly related– large n, then large E or small n, then small
E– And if v = c/ l then E and l are inversely
related– small l , large E or large l , small E
The Modern View of Light-Reference
118
Given a wave with wavelength of 5.6 X 10-
3 m, calculate the (a) frequency and (b) energy of the wave.
a) c = l n so v = c/ ln = 3.00 X 108 m x cycle = sec 5.6 X 10-3m n = 5.4 X 1014 cyc/secb) E = h n E =6.6 X 10-34 J. sec x 5.4 X 1014 cycles cycle secE = 3.6 X 10-19 Joules
The Modern View of Light-Reference
119
Given a wave with frequency 6.2 X 1014
cyc/sec, calculate the (a) wavelength and (b) energy of this wave
Let’s Do It!!!
120
Given a wave with frequency 6.2 X 1014
cyc/sec,calculate the (a) wavelength and (b)
energy ofthis wave(a) c = l n so l = c/v = l 3.00 X 108 m x sec = sec 6.2 X 1014 cycle l = 4.8 X 10-7 m/cycle(b) E = h n E = 6.6 X 10-34 J . sec x 6.2 X 1014 cycle cycle sec E = 4.1 X 10-19 Joules
Let’s Do It!!!
121
Matter and Energy Interact
• These things were known by the ancients:– Heat a lump of metal and it glows– Burn wood and it gives off light– Place an object in the sun and it can get
hotter• Today we understand that matter can
give off energy and it creates a spectrum
122
The EM Spectrum• EM spectrum- the full range of
frequencies of EM radiation • EM Spectrum includes:
– Radio waves– Infrared rays– Visible light– UV rays– X-rays– Gamma Rays
• Electromagnetic Spectrum Video on science 360
123
• Color is related to wavelength– White light- not a single color; made up of a
mixture of the seven colors of the rainbow and is all wavelengths mixed together
– A prism can separate white light into colors by different wavelength
– This is how rainbows are formed: sunlight is “split up” by raindrops
Visible Light in the EM Spectrum
125
Seeing Color
• The color an object looks depends on the colors of light it reflects
• For example, a red book only reflects red light:
Only red light is
reflected126
Purple light
White
light
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up
of red and blue):
A white hat would reflect all seven colors:
127
Review
• Number your paper from 1-5 and answer the following questions. Two will be cumulative review!
• 1. What is the mass of 50mL of water?– a. 50cm– b. 5mL– c. 50g– d. 50mg
128
Review
• C• 2. Why don’t the protons in the nucleus
repel each other and fly apart?• a. Repulsive force• b. Neutrino force• c. Positron emission• d. Strong force
129
Review
• D• 3. Which of these relationships, based
on the equation c = l n is true?• a. frequency goes up, the speed of light goes
down• b. wavelength goes up, frequency goes up• c. frequency goes up, wavelength goes down• d. frequency goes down, the speed of light
goes down
130
Review
• C• c = l n so v = c/ l or = l c/v and c
doesn’t change!• 4. If a shirt is black, what colors of the
visible spectrum are being reflected into your eyes from the shirt?• a. black• b. all• c. none• d. red, blue, and purple
131
Review
• C• 5. If a wave have a wavelength of 500
nm (500 x 10-9 m or 5.0 x 10-7 m) what color is it?• a. blue• b. yellow• c. red• d. purple
132
Bohr
• Examined the light released by atoms of certain elements– Worked mostly
with H since it has only 1 electron
– Used spectroscope to analyze light released from a vacuum tube
134
Bohr’s Energy Levels• Electrons reside in certain energy levels, or orbits• Are at least 7 levels and each represents a
different amount of energy• As long as an e- remains in one level, it
maintains the same amount of energy• Rungs of a ladder or stairs
135
Bohr’s Energy Levels• Lower energy levels
are closer to nucleus• Higher energy levels are farther• Ground state- electron in lowest energy level possible
– Atom can stay in the ground state indefinitely
– Electrons move only when energy is involved
136
Excited Atoms• Electrons can absorb
energy (called quanta or photons) and become excited – Greater the energy
absorbed, further from the nucleus they move
– Excited state is unstable so atom soon emits same amount of energy absorbed
– This can be seen as visible light!
137
Spectroscopy• When electrons move
from a higher energy level (further from the nucleus) to a lower energy level (closer to the nucleus), there is energy emitted– This energy is emitted
as light– These bands of light are
called the Emission Spectrum
138
• Only certain wavelengths or photon energies of light are present in the emission spectrum- Emission Video
• An element’s emission spectrum is unique to that element (like a fingerprint!)
Emission Spectrum-Reference
139
Absorption Spectrum-Reference
• Only certain wavelengths or photon energies of light are missing in the absorption spectrum
• An element’s absorption spectrum is unique to that element
140
For the same element’s atoms, the emission and absorption spectra will match each other so that if combined, they would yield continuous spectrum
This means that the same atoms release and absorb the same energies due to their electrons
Spectroscopy-Reference
141
Energy level diagram-Reference
A B C D
H emission spectrum
4 x 10-7m λ 7 x 10-7 m400nm 700nmsmaller λ larger λ
A C D
• 21 possible emission lines
U V Visible I R
violet red
• Absorption lines (arrows) would point UP
larger E smaller E
ENERGY
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2
3
4
5
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B
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Bohr Conclusions:
1. The electron is responsible for the emission and absorption spectra of light energy
2. The electron orbits the nucleus with a certain energy
3. When the electron absorbs energy, it moves to an orbit further from the nucleus, which causes the absorption spectrum
4. When the electron releases energy, it moves to an orbit closer to the nucleus, which causes the emission spectrum
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• Bohr tried to:– Apply his ideas about
electron behavior of hydrogen atoms to other elements’ atoms
– Explain the arrangement of elements on the periodic table by showing that elements in a column of the periodic table have similar chemical properties because they have similar electron structures
– Interactive Periodic Table
More Bohr…
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Summary of Bohr…
Bohr was correct about:1. The electron does have certain energies2. The electron is responsible for the emission
and absorption spectra of atoms3. There is a minimal (ground state) for the
electron which keeps the electron out of the nucleus
4. Chemical properties of elements are related to electron arrangement
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Summary of Bohr
Problems with Bohr’s ideas:1. Do not explain the behavior of atoms with
more than 20 electrons2. Violate the Heisenberg Uncertainty Principle
- both the path and velocity of a particle with the size and mass of the electron can not be determined at the same instant in time - in other words, electrons cannot be in orbits!
THEN WHERE ARE THEY?
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Erwin Schrodinger (1887-1961)
• In 1926, he further explained the nature of electrons in an atom:– The exact location of an
electron cannot be stated– It is more accurate to
view the electrons in regions called electron clouds-places where the electrons are likely to be found
• Won a Nobel Prize
Image taken from: nobelprize.org/.../1933/schrodinger-bio.html
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ReviewBohr and Atomic Spectra video
7min• Number your paper from 1-5 and
answer the following questions• 1. Which of these is a metric unit?
– a. pounds– b. cups– c. liters– d. inches
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Review
• C• 2. An isotope’s half-life
• a. can be changed by chemical reactions• b. is usually greater than 1000 years• c. is measured in time• d. is half the time required for the mass
to decay into another element
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Review
• B• 3. Which of these energy levels of an
atom is the level with the lowest energy?• a. n=1• b. n=2• c. n=4• d. n=6
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Review
• A• 4. What kind of spectrum is this?• a. super• b. absorption• c. electronic• d. emission
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Review
• B• 5. Which color of light represents the
largest release of energy, and therefore, the biggest jump between energy levels in Bohr’s model?• a. red • b. yellow• c. blue• d. purple
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