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

Access the best Study Guides, Lecture Notes and Practice Exams

Login

Join to view and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?