PACKET #14 – NUCLEAR CHEMISTRY



PACKET #9:

Nuclear Chemistry

Reference Table: N and O

[pic]

Name __________________________

Castle Learning username _______________________

Castle Learning Password _______________________

PACKET #9 – NUCLEAR CHEMISTRY

• The ratio of neutrons to protons is what determines whether a nucleus is stable or unstable.

• For elements whose atomic number are small (1-20), if the ratio of neutrons to protons (neutrons/protons) is about 1, the nucleus of the isotope are stable. Remember that isotopes have the same number of protons but different numbers of neutrons, or the same atomic number but different atomic mass.

RADIOACTIVITY: in radioactivity, the nucleus of an unstable isotope or element decays spontaneously and gives off rays and particles, which is also known as decay. The symbols for decay are listed below, the number on the top left indicates the mass of the decay, and the number on the bottom left indicates the charge of the decay.

• Transmutation: when the nucleus of an atom decays and one element changes into another element. The mass and charge have to be equal on both sides. Table R has the decay modes for radioactive isotopes that undergo Natural Transmutation, which means the decay (breakdown of the nucleus) occurs spontaneously.

• Artificial Transmutation: elements can be made radioactive by bombarding their nucleus with high energy particles. In natural transmutation, the element will change into another element when the nucleus decays. In artificial transmutation, the same thing occurs except not spontaneously. Remember that the atomic # and the mass # have to equal the same thing on both sides.

Table O:

[pic]

SEPARATING ALPHA, BETA, & GAMMA PARTICLES:

• Can be separated by using an electric or magnetic field. In an electric field, an alpha particle which is positively charged (has 2 protons) is deflected toward the negative electrode. A beta particle is negatively charged and will be deflected towards the positive electrode. Gamma rays have no charge, and therefore are not deflected, there is no bend.

Nuclear Energy: in a nuclear reaction, mass is converted into energy. Two types are fission and fusion.

• Fission: Type of artificial transmutation. A neutron bombards an atom causing it to split into two or more pieces and gives off a lot of energy. This is the energy behind nuclear power plants and atomic bombs (chain reaction).

• Fusion: two nuclei unite to form a heavier nucleus (“u”- unit). High temperature and pressure are needed which is why this occurs on the SUN. Fusion creates more energy than fission.

•

HALF-LIFE: Each radioactive isotope has its own rate of decay. Half-life is the time it takes a sample to decay in half. Table N lists some common half-life rates for some common isotopes. For every problem it’s important to determine how many half-lives occurred.

1 2 3

QUESTIONS:

1. What is the half-life?

• Total time elapsed

# half-life series

2. How much total time elapsed?

• Half-life x # half-life series

3. How many grams will remain after …?

• Must determine how many half-life series and then half the original amount by that many times (see example above)

4. What fraction remains?

• (1/2)#half-lives – knowing the fraction remaining will give you the number of half-life series.

(1/2)1 = ½ (1/2)4 = 1/16

(1/2)2 = ¼ (1/2)5 = 1/32

(1/2)3 = 1/8 (1/2)6 = 1/64

CHEMICAL VS. NUCLEAR ENERGY:

• Nuclear reactions release more energy than chemical reactions.

• Benefits: nuclear provides a lot of energy (produces the energy of the sun).

• Risks: Wastes from are very radioactive, must be stored for more than 100,000 years without leaking into the ground (long half-lifes). Accidents can cause radioactive spills (mutation/death).

RADIOACTIVE ISOTOPES (RADIOISOTOPES):

• Tracers:

o Carbon-14 – Date LIVING THINGS

o Uranium-238 & Lead 206 – Date NON-LIVING THINGS

• Medical: isotopes with very short half-lifes can be eliminated by the body quickly.

o Technetium-99 – brain tumors

o Iodine-131 – thyroid disorders

o Radium & Colbolt-60 – treatment of cancer

Risks:

• Biological Damage: exposure can damage or destroy cells – mutation.

• Long-term storage: must be stored in special containers for a long period of time, is it safe?

• Accidents: 1986 – Chernobyl, & Pollution: radioactive materials in air, water, food, and soil.

Nuclear Stability

• Some nuclei are stable (don’t change), but some are unstable. An unstable nuclei breaks down spontaneously giving off rays and particles.

• The ratio of neutrons to protons is what determines whether a nuclei is stable or unstable.

• Atoms with atomic numbers above 83 have NO stable isotopes

■ The ratio of neutrons to protons in stable nuclei is between 1:1 and 1.5:1, the higher ratio being associated with larger nuclei that have larger repulsive forces

Neutron

Proton

ARE THESE ISOPTOPES OF HYDROGEN STABLE?

1H 2H 3H

(hydrogen) (deuteron) (tritium)

Radioactivity [pic]

• In radioactivity, the nucleus of an unstable isotope or element decays spontaneously and gives off rays and particles. Table O lists the decay particles and rays.

[pic]

Decay Particles & Rays

• Alpha Decay: The nucleus decays and gives off alpha particles. Table O shows the symbols

MASS: +4

CHARGE: +2

• Beta Decay (electron): The nucleus decays and gives off beta particles. Table O shows the symbol. MASS: 0

CHARGE: -1

• Positron Decay: The nucleus decays and gives off positron particles. Table O shows the symbols MASS: 0

CHARGE: +1

• Gamma Ray: The nucleus decays and gives off gamma rays. Table O shows the symbol. MASS: 0

CHARGE: 0

**HIGHEST PENETRATING POWER**

[pic]

Separating Alpha, Beta, & Gamma Particles

[pic]

• The alpha particle is a positively charged particle. The alpha particle will be attracted to the negative side of the magnet (red) because the red is the negative end.

• The gamma particle has no charge, so it will not be attracted to either side.

• The beta particle is negatively charged particle. The beta particle will be attracted to the positive end of the magnet.

Transmutation

• When the nucleus of an atom decays and one element changes into another element.

• TWO TYPES: Natural & Artificial

• Natural Transmutations = Spontaneous

• Artificial Transmutations = NOT!! An element must be BOMBARDED with decay particles (remember Rutherford??)

[pic]

[pic]

[pic]

Natural Transmutation

• Table N – Selected Radioisotopes lists the decay mode for certain radioisotopes.

• MOST radioactive transmutation, like chemical reactions will conserve mass, energy, and charge.

[pic]

Natural Transmutation cont.

Question: Draw the correct transmutation for the radioactive isotope 220Fr. What element does it transmutate into?

220 87Fr ( 42He + X

220Fr spontaneously decays and

gives off alpha particles

Let’s Practice . . .

Determine the particle that is represented by X in each equation

1. 23090Th → 42He + X

2. 42He + 2713Al → X + 10n

3. 22789Ac → 0-1e + X

4. 42He + 147N → X + 11H

• For these transmutation questions, please note that they could ask you to solve for any variable: the initial radioactive isotope, the type of decay, or the transmutated element.

[pic]

Artificial Transmutation

• When the nucleus of an element is first bombarded with high energy particles!!

THEN it decays and changes into a new element!

**Artificial Transmutations are easy to spot!!

If you see an atom AND one of the high energy particles on left side of arrow combining to make a

new element on the right side of arrow, then it is an artificial transmutation!!

In other words:

Artificial Transmutations ( Have TWO reactants

Natural Transmutations ( Have ONE reactant

EXAMPLE: 2713Al + 42He ( 3015P + 10n

• Aluminum absorbs an alpha particle and releases a neutron to form phosphorus

• Absorption of an alpha particle by aluminum increases the mass by 4 from 27 to 31 and increases the atomic number by 2 from 13 to 15

• Loss of a neutron reduces the mass by 1 from 31 to 30 but does not effect the atomic number

[pic]

[pic]

Induced Nuclear Reactors

• All artificial transmutations, are induced by targeting a nucleus and bombarding it with a nuclear particle.

Particle Accelerators:

• A device that uses electric and magnetic fields to provide a bombarded nuclear particle with sufficient energy to induce a desired nuclear reaction

Nuclear Energy

• There are two types of nuclear reactions that we will discuss:

• Fission

• Fusion

IN FISSION AND FUSION REACTIONS, THE MASS OF THE PRODUCTS IS SLIGHTLY LESS THAN THE MASS OF THE REACTANTS.

SOME MASS IS CONVERTED TO ENERGY

Nuclear Fission

• One atom absorbs a neutron and splits into two or more pieces, giving off a tremendous amount of energy.

23592U + 10n → 23692U 14156Ba + 9236Kr + 310n + energy

• Fission occurs in nuclear reactors and the atomic bomb (chain reaction)

FISSION – “SPLIT”

[pic]

Nuclear Fusion

• When the two light nuclei unite to form a heavier nucleus.

21H + 21H → 42He

• This is the type of energy that exists on the SUN, and the HYDROGEN BOMB.

• Fusion requires extremely high temperature and pressure in order for it to occur.

• Fusion creates more energy than fission

FUSION – “UNITE”

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

Comparing Nuclear vs. Chemical Reaction

• Nuclear reactions release more energy than chemical reactions.

RISKS & BENEFITS OF NUCLEAR REACTIONS:

• Benefits: provide energy (produces the energy of the sun).

• Risks:

-Wastes from are very radioactive, must be stored for more than 100,000 years without leaking into the ground (long half-lives).

-Accidents can cause radioactive spills (mutation/death).

[pic][pic]

Half - Life

• The time required for half of the original sample of a radioisotope to decay.

NOTHING CAN CHANGE

THE

HALF LIFE OF A

RADIOISOTOPE!

Half - Life

• Half-life problems of all types are best solved by setting up a layout that shows the number of half lives, the mass, the time elapsed, and the fraction left. (any of these 4 variables can be the unknown)

• The one “equation” that you need to know is: Fraction remaining = (1/2)# of half-lives

EVERYTHING CAN BE SOLVED BY KNOWING THE NUMBER OF HALF LIVES THAT OCCUR!!

13153I has a half life of 8.07 days. A 10g sample was allowed to decay 32 days. What fraction remains?

# half lives = 32/8.07 = 4

Fraction left = (1/2)4 = 1/16

1 → ½ → ¼ → 1/8 → 1/16

100g of a radioactive isotope decays to 12.5g after 90.7 years.

What was the number of half lives? How long was each half-life?

100g → 50g → 25g → 12.5g 3 half lives

90.7 years/3 half lives = 30.2 years

A radioisotope has a half life of 10 days. 1g remains after 40 days. What was the initial amount (original amount) of the radioisotope?

Half life = 10 days

Time = 40 days

4 half lives passed

1 → 2 → 4 → 8 → 16 g

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

Uses of Radioactive Isotopes

. Radioactive Dating:

■ Geologic Dating: Based on half-life! Certain radioactive elements occur naturally in ROCK and so they are used to find the AGE of certain rocks!

• Examples: URANIUM-238 & LEAD-206

■ Dating Living Materials: Can help determine the age of wood, bone, animal skin, etc…

• Example: CARBON -14 & CARBON-12

5. Nuclear Power: Nuclear reactors are used for ELECTRICAL ENERGY!!

6. Industrial Measurement: Used to measure the thickness of certain metals.

• Example: Alpha, Beta, and Gamma particles!

[pic]

[pic]

[pic]

[pic]

[pic]

Review Questions

1) The stability of an isotope is based on the ratio of

A) electrons and protons

B) neutrons and electrons

C) neutrons and protons

D) atomic mass and atomic number

2) What is the neutron-to-proton ratio in a stable atom of carbon-12?

A) 1:2 B) 12:1 C) 2:1 D) 1:1

3) Which particle has the greatest mass?

A) an electron

B) a neutron

C) a beta particle

D) an alpha particle

4) In the diagram below, the radiation from a radioactive source is being separated as it passes between electrically charged plates.

[pic]

What are the three types of radiation observed on the detector?

A) X = alpha, Y = beta, Z = gamma

B) X = beta, Y = gamma, Z = alpha

C) X = gamma, Y = alpha, Z = beta

D) X = gamma, Y = beta, Z = alpha

5) According to the Selected Radioisotopes chemistry reference table, which is a decay product of Fe-53?

A) Cr-49 B) Mn-53 C) Co-53 D) Ni-47

6) Given the equation:

[pic]

What particle is represented by the letter X?

A) beta particle B) positron C) neutron D) alpha particle

7) What is represented by X in the equation below?

X ( 40 18Ar + 0 -1e

[pic]

8) Which equation represents nuclear disintegration resulting in the release of a beta particle?

[pic]

9) Bombarding a nucleus with high-energy particles that change it from one element into another is called

A) a breeder reaction

B) a half-reaction

C) natural transmutation

D) artificial transmutation

10) Which nuclear equation represents artificial transmutation?

[pic]

11) What type of reaction does the following equation represent? [pic]

A) fission B) fusion C) alpha decay D) beta decay

12) What type of reaction is represented by the equation below?

[pic]

A) natural transmutation B) fusion

C) fission D) thermonuclear

13) An original sample of a radioisotope had a mass of 10 grams. After 2 days, 5 grams of the radioisotope remains unchanged. What is the half-life of the radioisotope?

A) 4 days B) 2 days C) 5 days D) 1 day

14) What is the number of hours required for potassium-42 to undergo 3 half-life periods?

A) 6.2 hours B) 12.4 hours

C) 24.8 hours D) 37.2 hours

15) A radioactive isotope has a half-life of 10 years. What fraction of the original mass will remain unchanged after 50 years?

[pic]

-----------------------

Natural Transmutation

Artificial Transmutation

Weakest penetrating power-HEAVIEST

• Number on the upper left is the mass

• Number on the lower left is the charge

Strongest penetrating power-LIGHTEST

Fission

Fusion

50g

12.5g

25g

6.25g

10g

5g

2.5g

1.25g

1st half life

2nd half life

3rd half life

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download