CHM 142H Unit 5

_________ (radioactive decay) is the spontaneous emission of particles or electromagnetic radiation from unstable nuclei.

83

All elements having an atomic number > ____ are unstable and radioactive.

nuclear transmutation

___________ results from the bombardment of nuclei by neutrons, protons, or other nuclei.

mass number

The superscript denotes the ________ (proton + neutrons).

atomic number

The subscript is the ______ (protons).

atomic orbital

Superscript of 0, subscript of -1, with e represents an electron in or from a _______.

nucleus

Superscript of 0, subscript of -1, with beta represents an electron that comes from a _______.

positron

The ______ has the same mass as the electron, but bears a charge of +1.

alpha

An ___ particle is identical to a helium-4 nucleus and can be represented either as superscript 4, subscript 2, with an He or alpha.

nucleus

The _____ occupies a small portion of the total volume of an atom, but it contains most of the atom’s mass.

coulombic repulsion, short-range attraction

From Coulomb’s law, we know that like charges repel and unlike charges attract. The stability of any nucleus is determined by the difference between _______ and the ________.

neutron to proton ratio

The principal factor that determines nuclear stability is the __________ (n/p).

belt of stability

Stable nuclei are located in an are of the graph known as the ___________. Most radioactive nuclei lie outside of it.

1

For stable elements having low atomic number (</= 20), the n/p is close to ___.

increases

As atomic number increases, the n/p ____.

higher, beta particle emission

Above the belt of stability, nuclei have ____ n/p ratios. To lower this ratio, these nuclei undergo ______. Increases number of protons, decreases number of neutrons.

lower, positron

Below the belt of stability, nuclei have ____ n/p ratios. To increase this ratio, these nuclei may emit a _____.

electron

A nucleus may also undergo _____ capture.

electron capture

_______ is the capture of an electron — usually a 1s electron — by the nucleus.

decreases

Electron capture has the same net effect on the nucleus as positron emission, the atomic number ______ by 1.

nuclear binding energy

A quantitative measure of nuclear stability is the __________, which is the energy required to break up a nucleus into its component protons and neutrons.

nucleons

The masses of nuclei are always less than the theoretical sum of the masses of the _______, which is a general term for the protons and neutrons in a nucleus.

mass defect

The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons is called the ________.

surroundings

The loss in mass shows up as energy (heat) given off to the ______ (exothermic).

delta E

_______ = energy of product - energy of reactants

delta m

______ = mass of product - mass of reactants

negative

Delta E and delta m are _____ quantities.

nuclear binding energy per nucleon

When comparing the stability of any two nuclei, we must account for the fact that they have different numbers of nucleons. It makes more sense to compare nuclei using the _______________, which = nuclear binding energy/number of nucleons.

stable

The greater the nuclear binding energy per nucleon, the more _____ the nucleus.

40 and 100

The highest binding energies per nucleon belong to elements with intermediate mass numbers —- between _______ —- and are greatest for elements in the Fe, Co, and Ni region of the periodic table.

chemical reactions

1. Atoms are arranged by the breaking and forming of chemical bonds.

2. Only electrons in automatic or molecular orbitals are involved in the reaction.

3. Reactions are accompanied by the absorption or release of relatively small amounts of energy.

4. Rates of reaction are influenced by temperature, pressure, concentration, and catalysts.

nuclear reactions

1. Elements are converted to other elements or isotopes.

2. Protons, neutrons, electrons, and other subatomic particles such as a particles may be involved.

3. Reactions are accompanied by the absorption or release of tremendous amounts of energy.

4. Rates of reaction normally are not affected by temperature, pressure, or catalysts.

nuclear

Radioactive decay and nuclear transmutation are ______ reactions.

radioactive decay series

A ___________ is a sequence of nuclear reactions that ultimately result in the formation of a stable isotope.

nuclear reaction

It is important to balance the ______ for each step in a radioactive decay series.

parent, daughter

In radioactive decay steps, the beginning radioactive isotope is called the _____ and the product isotope is called the _____.

first order kinetics

All radioactive decays obey _________. The rate of radioactive decay at any time t is given by t = kN, where k is the first-order rate constant and N is the number of radioactive nuclei present.

number of molecules

In nuclear reactions use __________ (N) instead of concentration.

half lives

The _______ of radioactive isotopes have been used as atomic clocks to determine the ages of certain objects.

living mater

To determine the age of an object, we measure the activity of 14C and compare it to the activity of 14C in _______.

rocks

A uranium decay series is suitable for estimating the age of ____ found on earth and of extraterrestrial objects.

first step

As a good approximation, we can assume that the half life for the overall process is equal to the half life of the _____ because it is the slowest.

collision

Nuclear transmutation differs from radioactive decay in that transmutation is brought about by the ______ of two particles.

reactant, product, bombarding, emitted

In nuclear transmutation, the species written first is a ____ and the species written last is a _____. Within the parentheses, the ________ particle is written first, followed by the _______ particle.

transuranium elements

Particle accelerators made it possible to synthesize transuranium elements, elements with atomic numbers greater than 92.

bombarding

Light elements can be made radioactive by _____ their nuclei with appropriate particles.

kinetic energy

In nuclear transmutation, positively charged must have considerable _______ to overcome the electrostatic repulsion between themselves and the target nuclei.

particle accelerator

A ______ uses electric and magnetic fields to increase the kinetic energy of charged species so that a reaction will occur.

spiral path

Alternating the polarity on specially constructed plates causes the particles to accelerate along a ____. When they have sufficient energy, they are guided out of the accelerator into a collision with a target substance.

linear path

In nuclear transmutation, particles may also be accelerated along a _______.

nuclear fission

________ is the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons.

nuclear fission

This process releases a large amount of energy.

slow neutrons

Uranium - 2235 undergoes nuclear fission when bombarded with _______.

produced, captured

During uranium - 235 fission, more neutrons are ______ than are originally _______ during the process. This property makes possible a nuclear chain reaction.

nuclear chain reaction

A ___________ is a self-sustaining sequence of nuclear fission reactions.

subcritical

If there is not enough uranium - 235 to capture the neutrons, the chain reaction will not occur and the mass of the sample is said to be _______.

critical mass

When the amount of fissionable material is >/= ________, the minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction, a chain reaction occurs.

atomic bomb

The first application of nuclear fission was the ________. Critical mass is formed using conventional explosive, such as TNT< to force the fissionable sections together. Neutrons from a source at the center of the device trigger the nuclear chain reaction.

electricity

Nuclear fission is also used in the generation of _______.

control rods, moderator

In the generation of electricity, slow neutrons split uranium - 235 nuclei more efficiently than fast ones. For greater efficiency, neutrons must be slowed down. In a nuclear reactor, ______ and a ______ work together to manage the chain reaction.

neutrons

With nuclear fuel, the factor limiting the rate of the reaction is the number of ______ present.

control rods

In nuclear fuel the factor limiting the rate of the reaction can be controlled by lowering cadmium or boron ________ between the fuel elements. These rods capture neurons.

slow down

Moderators ______ neutrons to improve efficiency.

requirements of a good moderator

1. It should be nontoxic and inexpensive

2. It should resist conversion into a radioactive substance by neutron bombardment.

3. It should be. fluid so that it can also be used as a coolant.

light water reactors

Nuclear reactors that use light water as a moderator are called _________ because subscript 1, superscript 1, H is the lightest isotope of the element hydrogen.

moderator

Another type of nuclear reactor used D2O, or heavy water, as the ______.

neutrons, efficient

Deuterium absorbs ____ much less efficiently than does ordinary hydrogen. The reactor is more _____ and does not require enriched uranium. However, D2O must be prepared which can be expensive considering the amount of water used in a nuclear reactor.

breeder reactor

A _________ uses uranium fuel, but unlike a conventional nuclear reactor, it produces more fissionable materials than it uses.

238

In a breeder reactor, when uranium - ____ is bombarded with fast neutrons, many reactions take place.

disadvantages of breeder reactors

1. Very expensive compared to conventional reactors.

2. There are also more technical difficulties associated with the construction of such reactors.

3. Risk of accidents.

4. Radioactive waste disposal.

nuclear fusion

_____ is the combining of small nuclei into larger ones.

released

When two light nuclei combine to form a larger, more stable nucleus, an appreciable amount of energy will be ______ in the process (look at binding energy).

15 million

The sun is made up of mostly hydrogen and helium. Nuclear fusion occurs constantly in the sun where temperatures reach about ______ degrees Celsius.

thermonuclear reactions

Because fusion reactions take place only at very high temperatures, they are often called _____________. These temperatures are a major concern in choosing the proper nuclear fusion process for energy production.

advantages of nuclear fusion

1. Fuels are cheap and almost inexhaustible.

2. The process produces little radioactive waste. No danger of a meltdown.

plasma

In nuclear fusion, many technical difficulties are due to the extreme temperature. At temperatures of about 100 million degrees Celcius, molecules exist in a state of matter called ______. No solid container can exist at such temperatures to contain this.

plasma

A gaseous mixture of positive ions and electrons

magnetic confinement

One approach to solving the nuclear fusion of high temperatures problem is to use _________, which is when plasma moves through a doughnut-shaped tunnel, confined by a complex magnetic field.

hydrogen, thermonuclear

The _____ bomb, also called the _______ bomb, contains solid lithium deuteride (LiD).

fission, fusion

The denotation of a hydrogen bomb occurs in two stages — first a ___ reaction then a ____ reaction.

In the denotation of a hydrogen bomb, the required temperature for fusion is achieved with an ____