Download DP Physics Unit 7 Quiz Review: Name

DP Physics Unit 7 Quiz Review:
Name: _____________________________
1. Explain the difference between Thompson’s Plum Pudding Model and Rutherford’s Atomic
Model.
By 1911 the components of the atom had been discovered. The atom consisted of subatomic particles called protons
and electrons. However, it was not clear how these protons and electrons were arranged within the atom. J.J.
Thomson suggested the"plum pudding" model. In this model the electrons and protons are uniformly mixed
throughout the atom:
Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Rutherford reasoned that if
Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high
velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles. He
decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil
but to his amazement a few alpha particles rebounded almost directly backwards.
These deflections were not consistent with Thomson's model. Rutherford was forced to discard the Plum Pudding
model and reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an
atom was concentrated in a nucleus. He thus developed the planetary model of the atom which put all the protons in
the nucleus and the electrons orbited around the nucleus like planets around the sun.
2. Explain the difference between the concept of continuous spectrum, absorption spectrum, and
emission spectrum.
When you shine white light through a prism, you find out that it contains a rainbow of colors. This is called
dispersion, and it happens because light of different wavelengths (colors) refracts (bends) by different amounts
inside the prism.
The rainbow could be described as a spectrum, and if the spectrum goes all the way from red to violet, with no gaps,
then it is a continuous spectrum.
The gaps in the Sun's spectrum are called absorption lines, and they give us valuable information about the Sun.
Here's how it works:
The Sun contains elements like hydrogen and helium. When the sunlight (including ultraviolet and infrared that we
can't see) shines through these elements, they absorb the energy, but they only absorb electromagnetic waves that
are just the right color to match the energy they need. This gives us those gaps in the Sun's spectrum.
Each element in the universe has a different combination of absorption lines, so we can use the Sun's absorption
spectrum to figure out what elements are present in the Sun. This is how we know what the Sun is made of.
An emission spectrum is the opposite of an absorption spectrum. Instead of getting a mostly continuous spectrum,
with a few particular colors missing, in an emission spectrum we only get those few particular colors. These are
called emission lines.
3. What are the Lyman Series, Balmer Series, and Paschen Series?
4. Explain the difference between an excited atom and de-excited atoms, include energy level,
energy absorption and energy emission in your explanation.
In quantum mechanics an excited state of a system (such as an atom, molecule or nucleus) is any
quantum state of the system that has a higher energy than the ground state (that is, more energy than the
absolute minimum). Excited atoms gain (absorb) energy and push the electron into a higher orbit (higher
energy level). The de-excited atoms do the opposite. Instead of gaining energy, it loses energy (emit)
and release it as photons. The electron drops back to the lower energy level.
5. What is the relationship between energy and frequency?
c
E = h 
hc/
c = light speed (3.00 x 108 m/s)
 = wavelength
h = Planck’s constant (6.626 x 10-34 Js)
6. What is the relationship between energy and wavelength?
hc/
x10-25/
7. What is meant by nuclear stability?
Isotopes: Atoms with the same number of protons, but with different numbers of neutrons.
Isotopes have the same atomic number and are the same element, but have different mass numbers.
Isotopes are generally named by their mass numbers, such as rubidium-85 and rubidium-87.
Isotopes are often represented using the symbol:
where:
M is the chemical symbol for the element. A is the mass number. Z is the atomic number.
Stable isotopes: Isotopes that have stable nuclei and do not emit radiation.
Radioisotopes: Isotopes that have unstable nuclei and emit radiation.
For some elements, all isotopes are radioactive, such as uranium and radium.
For some elements, only one or some isotopes are radioactive, such as rubidium and rhenium, which each have two
isotopes, with only one being radioactive.
The nucleus of an isotope can be unstable for several reasons:
If there are too many neutrons for the number of protons, a neutron changes to a proton and an electron, with the
emitted electron being known as a negative beta (β-) particle. This occurs in the case of cobalt-60.
If there are too many protons for the number of neutrons, a proton changes to a neutron and a positron, with the
emitted positron being known as a positive beta (β+) particle. This occurs in the case of sodium-22.
If there are too many protons and neutrons (the nucleus is too heavy), two protons and two neutrons are emitted
from the nucleus as a helium nucleus or an alpha (α) particle, such as in the case of radon.
Plot of atomic isotopes
8. What is an isotope?
Each of two or more forms of the same element that contain equal numbers of protons but different numbers of
neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a
radioactive form of an element. Example:
9. What is a species or a nuclide?
A nuclide is a type of atom whose nuclei have specific numbers of protons and neutrons (both are called nucleons).
Therefore, nuclides are composite particles of nucleons.
According to the standard model, up and down quarks are the basic components of nucleons. Thus, nuclides can
also be considered composite particles of quarks
The term isotopes is often used to mean nuclides, because a nuclide is usually an isotope of an element. Strictly
speaking, isotopes are atoms with the same number of protons but different number of neutrons in their nuclei.
For example, a carbon-14 nuclide is the nucleus of a carbon atom, which has six protons, with mass number 14
(thus having eight neutrons)
10. What is the relationship between the Atomic Mass, number of protons and number of
neutrons?
Atomic number (Z) is the number of protons in the nucleus of an atom. It is also equal to the
number of electrons since the atom is electrically neutral.
Mass number (A) is the total number of neutrons and protons present in the nucleus of an atom.
The mass number of elements in most of the cases is approximately twice the value of their atomic
number. This indicates that the neutron-proton (n/p) ratio of such elements is close to unity. However, it is
not so in case of some heavy metals.
11. Explain nucleon force (strong force)
The Strong Nuclear Force (also referred to as the strong force) is one of the four basic
forces in nature (the others being gravity, the electromagnetic force, and the weak nuclear
force). As its name implies, it is the strongest of the four. However, it also has the shortest
range, meaning that particles must be extremely close before its effects are felt. Its main
job is to hold together the subatomic particles of the nucleus (protons, which carry a
positive charge, and neutrons, which carry no charge. These particles are collectively called
nucleons).
like charges repel (+ +, or - -), and unlike charges attract (+ -).
If you consider that the nucleus of all atoms except hydrogen contain more than one
proton, and each proton carries a positive charge, then why would the nuclei of these atoms
stay together? The protons must feel a repulsive force from the other neighboring protons.
This is where the strong nuclear force comes in. The strong nuclear force is created between
nucleons by the exchange of particles called mesons. This exchange can be likened to
constantly hitting a ping-pong ball or a tennis ball back and forth between two people. As
long as this meson exchange can happen, the strong force is able to hold the participating
nucleons together.
The nucleons must be extremely close together in
order for this exchange to happen. The distance required is about the diameter of a proton
or a neutron. If a proton or neutron can get closer than this distance to another nucleon,
the exchange of mesons can occur, and the particles will stick to each other. If they can't
get that close, the strong force is too weak to make them stick together, and other
competing forces (usually the electromagnetic force) can influence the particles to move
apart. This is represented in the following graphic. The dotted line surrounding the nucleon
being approached represents any electrostatic repulsion that might be present due to the
charges of the nucleons/particles that are involved. A particle must be able to cross this
barrier in order for the strong force to "glue" the particles together.
In the case of approaching protons/nuclei, the closer they get, the more they feel the
repulsion from the other proton/nucleus (the electromagnetic force). As a result, in order to
get two protons/nuclei close enough to begin exchanging mesons, they must be moving
extremely fast (which means the temperature must be really high), and/or they must be
under immense pressure so that they are forced to get close enough to allow the exchange
of meson to create the strong force. Now, back to the nucleus. One thing that helps reduce
the repulsion between protons within a nucleus is the presence of any neutrons. Since they
have no charge they don't add to the repulsion already present, and they help separate the
protons from each other so they don't feel as strong a repulsive force from any other nearby
protons. Also, the neutrons are a source of more strong force for the nucleus since they
participate in the meson exchange. These factors, coupled with the tight packing of protons
in the nucleus so that they can exchange mesons creates enough strong force to overcome
their mutual repulsion and force the nucleons to stay bound together. The preceding
explanation shows the reason why it is easier to bombard a nucleus with neutrons than with
protons. Since the neutrons have no charge, as they approach a positively charged nucleus
they will not feel any repulsion. They therefore can easily "break" the electrostatic repulsion
barrier to being exchanging mesons with the nucleus, thus becoming incorporated into it.
12. What is radioactive decay and why do radioisotopes decay?
Radioactive decay is the spontaneous breakdown of an atomic nucleus resulting in the release of energy
and matter from the nucleus. Remember that a radioisotope has unstable nuclei that does not have
enough binding energy to hold the nucleus together.
13. Explain the three different decays include what is gain and what is lost.
Alpha decay is usually restricted to the heavier elements in the periodic table. (Only a handful of nuclides
with atomic numbers less than 83 emit an -particle.) The product of -decay is easy to predict if we
assume that both mass and charge are conserved in nuclear reactions. When a nucleus emits an alpha
particle () it loses two protons and two neutrons.
Alpha decay of the 238U "parent" nuclide, for example, produces 234Th as the "daughter" nuclide.
The sum of the mass numbers of the products (234 + 4) is equal to the mass number of the parent nuclide (238),
and the sum of the charges on the products (90 + 2) is equal to the charge on the parent nuclide.
Electron emission (- ) is literally the process in which a neutron becomes a proton and an electron is ejected or
emitted from the nucleus. When this happens, the charge on the nucleus increases by one. Electron emitters are
found throughout the periodic table, from the lightest elements ( 3H) to the heaviest (255Es). The product of emission
can be predicted by assuming that both mass number and charge are conserved in nuclear reactions. If 40K is a
emitter, for example, the product of this reaction must be 40Ca.
Once again the sum of the mass numbers of the products is equal to the mass number of the parent nuclide and the
sum of the charge on the products is equal to the charge on the parent nuclide.
The other beta decay is called positron emission. The positron is the antimatter equivalent of an electron. It has the
same mass as an electron, but the opposite charge. Positron decay is when proton becomes a neutron and
produces a daughter nuclide with one less positive charge on the nucleus than the parent.
Positrons have a very short life-time. They rapidly lose their kinetic energy as they pass through matter. As soon as
they come to rest, they combine with an electron to form two -ray photons in a matter-antimatter annihilation
reaction.
The daughter nuclides produced by -decay or - are often obtained in an excited state. The excess energy
associated with this excited state is released when the nucleus emits a photon in the -ray portion of the
electromagnetic spectrum. Most of the time, the -ray is emitted within 10-12 seconds after the -particle or -. In
some cases, gamma decay is delayed, and a short-lived, or metastable, nuclide is formed, which is identified by a
small letter m written after the mass number. 60mCo, for example, is produced by the electron emission of 60Fe.
The metastable 60mCo nuclide has a half-life of 10.5 minutes. Since electromagnetic radiation carries neither charge
nor mass, the product of -ray emission by 60mCo is 60Co.
14. What is a neutrino?
Neutrinos a neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal
matter. Three kinds of neutrinos are known, associated with the electron, muon, and tau particle. In order to
conserve energy it was postulated that another particle called a neutrino  was created to carry the additional EK
needed to balance the energy.
15. What is half-life?
The half-life of a radioactive substance is a characteristic constant. It measures the time it takes for a
given amount of the substance to become reduced by half as a consequence of decay, and therefore,
the emission of radiation.
Calculations: