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PHY 102: TEST 5
What was the main problem with J. J. Thomson’s plum pudding model of the atom?
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It couldn’t reproduce experimental data.
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J. J. Thomson’s model of the atom
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A. had electrons embedded in some kind of fluid that contained most of the mass of the atom.
B. held that the fluid containing most of the mass of the atom had enough positive charge to make the atom electrically neutral.
C. failed to predict the observed frequencies of the atom.
D. depended upon electric forces to produce stability.
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The Bohr model of the atom is akin to a
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miniature solar system.
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What is the lowest energy level in an atom called?
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Ground state
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True or False: In the Bohr model of the atom, electrons can orbit the nucleus with any radius.
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false
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Alpha particles are repelled by atomic nuclei because
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A. of the electric force between an alpha particle and the atomic nucleus.
B. closeness of each to each other is not permitted.
C. the force between the alpha particle and the atomic nucleus is opposite to an attractive force.
D. they both have the same sign of electric charge.
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Some alpha particles fired through a gold foil bounce backward by
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A. making direct hits with gold atoms.
B. electrostatic repulsion with the electron clouds of gold atoms.
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In the periodic table, elements in the same ______ have very similar properties.
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column |
The periodic table is ordered by
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atomic number
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True or False: The spectrum of a hydrogen atom is the same as the spectrum of a helium atom.
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false
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How many electrons are in a neutral oxygen atom?
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8
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True or False: When an electron transitions from the first excited state to the ground state it gives off energy.
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true
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What do electrons have that protons always have in equal magnitude?
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charge
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The atomic number is the number of ______ in an atom.
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protons or electrons
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Who was the scientist to first create the periodic table?
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D. Dmitri Mendeleev
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An excited hydrogen atom is capable of emitting radiation of
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many more than 3 frequencies
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When an electron transitions from the 2nd excited state to the first excited state, it gives off
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a photon
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Your friend tells you that she has discovered a new element with atomic number 156. How many electrons are in the new element?
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156 |
A certain radioactive isotope placed near a Geiger counter registers 120 counts per minute. If the half-life of the isotope is one day, what will the count rate be at the end of four days?
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7.5 counts/min
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The half-life on an isotope is one day. At the end of three days, how much of the isotope remains?
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one-eighth
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What makes an element distinct?
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the number of protons
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The half-life of carbon-14 is 5730 years. If a 1-gram sample of old carbon is 1/8 as radioactive as 1-gram of a current sample, then the age of the old sample is about
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17,200 years.
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A certain radioactive isotope placed near a Geiger counter registers 160 counts per second. Eight hours later, the counter registers 10 counts per second. What is the half-life of the isotope?
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2 hours
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True or False: If a 20 kg brick is made entirely of radioactive atoms of half-life 5 days, at the end of 5 days this brick will have a mass of 10 kg.
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true
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The atomic number of an element is the same as the number of its
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protons
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True or False: If half of a radioactive substance decays in the first 10 s, the other half will decay in the next 10 s.
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false
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Which radiation has no electric charge associated with it
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gamma rays
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The mass of a nucleus is exactly equal to the sum of the masses of its individual
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A. separated protons.
B. separated neutrons.
C. separated electrons.
D. all of these
******E. none of these
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When a beta particle is ejected from a nucleus, the nucleus then has a greater
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charge |
The nucleus with the greatest mass is
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plutonium.
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What type of radiation is most dangerous to humans?
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gamma
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When U-238 emits an alpha particle, the nucleus left behind has
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90 protons
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Uranium-235, uranium-238 and uranium-239 are different
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isotopes
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The rate of radioactive decay is proportional to the
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number of nuclei.
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The atomic mass number of an element is approximately the same as the number of its
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protons and neutrons.
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What is the most recent major nuclear reactor accident?
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Fukushima
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In the fissioning of uranium, a chain reaction is caused by
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ejected neutrons.
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Which of the following is NOT an application of radioactivity?
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steel manufacturing
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Control is exercised in a nuclear reactor by
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absorbing excess neutrons with control rods.
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A sphere of pure U-235 will explode if it is
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big enough
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A radioactive source has a half-life of 4 minutes. At t = 0, it is placed near a geiger counter and the count rate is 3000 counts/sec. What is the count rate at t = 12 minutes? Round your answer to 1 decimal place.
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375 |
500 bc greek philosphers
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believed smallest pieces of matter were atoms-- now we know atoms are not the smallest
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500 bc greek philosphers
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believed smallest pieces of matter were atoms-- now we know atoms are not the smallest
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1897- JJ Thompson discovered the electron thomas model of atom
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"plum pudding model"-- experimental tests showed thomson model was wrong-- couldn't predict spectra
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spectra: colors of light emitted by atoms
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... |
1911- rutherford gold foil experiment
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shoot electrons at gold foil, some didn't go through but bounced back- must be nucleus of positive charge -1/1000 particles bounces back
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Neils Bohr
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Refined Rutherfords model (electrons can only orbit in discrete (well- defined) orbits)-- in one or the other orbit... not both @ the same time
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ground excited state
1st excited state
2nd excited state
3rd excited state
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n=1
n=2
n=3
n=4
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ground state radius
1st excited state radius
2nd excited state radius
3rd excited state radius
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ro
4ro
9ro
16ro
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ground state energy
1st excited state energy
2nd excited state energy
3rd excited state energy
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Eo
1/4Eo
1/9Eo
1/16Eo
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Radius
rn=n^2ro
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Radius increase when n increases
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Energy
En=Eo/n^2
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Energy decreases when n increases
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Ground state energy
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negative |
To move electron to a larger orbit, you must...
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add energy
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Amount of energy required is equal to the
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difference in energies between the two orbits
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spectrums
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Different colors of light come from electrons moving to smaller orbits
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Each atom has a different number of
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protons and electrons
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Periodic table organized by
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Properties |
Atomic number
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# of protons/ electron
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Atomic mass
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# of protons and neutrons
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Elementes in the same column (vertical) have the similar
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properties |
The nucleus contains
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protons and neutrons
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#neutrons=
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(atomic mass)
-
(atomic #)
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Protons |
determines the type of atom
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isotope
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same type of atom with different number of neutrons
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Radioactivity
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emission of a particle by a nucleus
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radioactivity changes...
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chemical properties
mass of atom
charge of nucleus
identity of atom
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4 types of radiation
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alpha particle (helium nucleus)
beta particle (electron)
gamma particle (light)
neutron
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Alpha particle (helium nucleus)
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charge=+2
mass=4
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Beta particle (electron)
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charge=-1
mass=0
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Gamma particle (light)
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charge=0
mass=0
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neutron
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charge=0
mass=1
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Mass units
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atomic mass units (amu)-- what's on the periodic table
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Penetrating power
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Depth that radioactive particle can travel before stopping
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Alpha |
stopped by paper
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beta |
stopped by aluminum
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gamma
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stopped by lead
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gamma
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random process if there are a lot of atoms, we can get average information about when they decay-- rate proportional to # atoms
***more atoms= more that decay
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Half-life
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Time it takes for half the sample to decay
*** applies to
#nuclei
mass of sample
count rate (counts per minute)
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Applications of radioactivity
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watch dials/ medicine
food safety
smoke detectors
radon mitigation
nuclear medicine
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Fission
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splitting of nucleus
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Centrifuge
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used to seperate nuclear isotopes
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To control chain reaction, use...
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control rods to absorb some neutrons
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Fusion |
Combine nuclei
energy released
sun
**Cold fusion doesn't exist
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