01:160:159 Lecture 21: chap21notes

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AP Chemistry Chapter 21 - The Nucleus: A Chemist’s View

21.1 Nuclear Stability and Radioactive Decay

A. Radioactive Decay

1. Decomposition forming a different nucleus and producing one or

more particles

a. Total mass number and atomic number must be conserved in

any nuclear change

49 Be + 24 He→126C + 01 n

B. Zone of Stability

1. Of 2000 known nuclides, only 279

are stable with respect to radioactive

decay

2. All nuclides with more than 83

protons (bismuth) are unstable

3. Light nuclides are most stable

when the neutron/proton ratio is 1

4. Heavier nuclides are most

stable when the neutron/proton

ratio is greater than 1

5. Magic numbers

a. Special stability exists when the number of protons or neutrons

is: 2, 8, 20, 28, 50, 82, 126

C. Types of Radioactive Decay

1. Alpha Emission

a. Alpha particle () is a helium nucleus ( 24 He ), so it has a 2+ charge

b. Alpha emission is restricted almost entirely to very heavy nuclei

21084Po + →20682Pb + 24 He

2. Beta Emission

a. Beta particle () is an electron emitted from the nucleus

during nuclear decay

01 n → 11 p + −10



b. Beta particles are emitted when a neutron is converted into a proton

and an electron

146C → 147 N + −10



3. Positron Emission

a. Positrons are particles that have the same mass as an electron, but

a positive charge

b. Positron emission arises from the conversion of a proton into

a neutron and a positron

11 p → 01 n + +10



1938 K → 1838 Ar + +10



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4. Electron Capture

a. Inner orbital electron is captured by the nucleus of its own atom

b. Electron combines with a proton and a neutron is formed

−01 e + 11 p ® 01n 10647 Ag + −01 e ® 10646 Pd

5. Gamma Emission

a. Gamma rays () are high-energy electromagnetic waves emitted

from a nucleus as it changes from an excited state to a ground

energy state

b. Gamma rays are produced when nuclear particles

undergo transitions in energy levels

c. Gamma emission usually follows other types of decay that leave

the nucleus in an excited state

D. Decay Series

1. In some cases, multiple decays are needed to produce a stable nuclide

a. Original nuclide is called the "Parent" nuclide

b. Ensuing decay nuclides are called "daughter" nuclides

21.2 The Kinetics of Radioactive Decay

A. Rate of Decay

1. The negative of the change in the number of particles per unit of time

Rate = -

µ N

Rate = -

= k N

a. This is a first order rate law, so…

ln ç

= -kt

N0 = original number of nuclides (at t = 0)

N = the number of nuclides remaining at time t

B. Half-Life (t1/2)

1. The time required for the number of nuclides to reach half the original value

= ln( 2) = 0.693

k k

t1 / 2

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Document Summary

Ap chemistry chapter 21 - the nucleus: a chemist"s view. 21. 1 nuclear stability and radioactive decay: radioactive decay, decomposition forming a different nucleus and producing one or more particles, total mass number and atomic number must be conserved in any nuclear change, zone of stability. 4 he ), so it has a 2+ charge. 4 he: beta emission, beta particle ( ) is an electron emitted from the nucleus during nuclear decay. 0: beta particles are emitted when a neutron is converted into a proton and an electron. 0 : positron emission, positrons are particles that have the same mass as an electron, but a positive charge, positron emission arises from the conversion of a proton into a neutron and a positron. 0 : electron capture, inner orbital electron is captured by the nucleus of its own atom, electron combines with a proton and a neutron is formed.

Related Questions

Nuclear Decay Equations

Learning Goal:

To predict the products of alpha emission, beta emission, positron emission, and electron capture.

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. There are five major types of radioactive decay:

Alpha (Î±) radiation consists of helium nuclei. The helium nucleus is a small particle containing two protons and two neutrons (42He).

Beta (Î²) radiation consists of electrons. In nuclear equations, the standard format for representing a beta particle using superscripts and subscripts is 0â1e.

Positron emission results from the conversion of a proton in the nucleus to a neutron. The ejected positron is a particle that has the same mass as an electron but an opposite charge. In nuclear equations, the standard format for representing a positron using superscripts and subscripts is 01e .

Electron capture is the capture of an inner shell electron by a proton in the nucleus. The process emits gamma (Î³) radiation and results in a proton converting to a neutron. Gamma radiation consists of high-energy electromagnetic radiation.

Gamma (Î³) radiation consists of high-energy radiation, and contains no particles and thus they have no mass. In nuclear equations, the standard format for representing gamma radiation using superscripts and subscripts is 00Î³.

Balancing a decay equation

There are two main rules to remember when balancing nuclear equations:

The total of the superscripts in the reactants and products must be the same.

The total of the subscripts in the reactants and products must be the same.

For an isotope of an element, the superscripts are mass numbers, and the subcripts are atomic numbers:

Mass number â¶ AAtomic number â¶ Z X âµ Chemical symbol

Where the mass number (A) is the sum of the number of proton and number of neutrons in the nucleus, atomic number (Z) is the number of protons in the nucleus, and chemical symbol (X) is the symbol of the specific element.

Part A

Identify the nuclide produced when americium-241 decays by alpha emission:

241 95Amâ42He + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part B

Identify the nuclide produced when phosphorus-32 decays by beta emission:

3215Pâ 0â1e + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part C

Identify the nuclide produced when fluorine-18 decays by positron emission:

18 9Fâ01e + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

Part D

Identify the nuclide produced when thallium-201 decays by electron capture:

201 81Tl+ 0â1eâ00Î³ + ?

Express your answer as an isotope using prescripts.

SubmitHintsMy AnswersGive UpReview Part

1. (1 point) What might be damaged by ionizing radiation? * paper soft tissue wood lead

2. (1 point) When an atom emits an beta particle, what is the change in the atomic number? * no change decrease by 1 decrease by 2 increase by 1 increase by 2

3. (1 point) What is the change in atomic mass caused by the emission of gamma radiation? * no change decrease by 1 decrease by 2 increase by 1 increase by 2

4. (1 point) Which of the following materials would effectively stop gamma radiation? * one foot of concrete single sheet of paper thin pieces of wood three inches of lead

5. (1 point) When the ratio of neutron-to-proton dictates that a neutron must break down it will form _________. * A helium nucleus An alpha particle A proton and an electron Two protons

6. (1 point) What determines the type of decay if a nucleus falls outside the band of stability? * the ratio of alpha particles to beta particles the ratio of beta particles to alpha particles the ratio of neutrons to protons the ratio of protons to neutrons

7. (1 point) A positron is emitted when ____________. * an alpha particle forms a beta particle forms proton converts to a neutron neutron converts to a proton

8. (1 point) How does an atom with too few neutrons relative to protons undergo radioactive decay? * by converting proton to a neutron by converting a neutron to a proton by emitting an alpha particle by emitting a beta particle

9. (1 point) How much of the original sample would remain after two half lives have past? * There would be nothing of the original left There would be half of the original sample still there There would be one quarter of the sample still present There would only be one eighth of the original sample still present

10. (1 point) What is the approximate half life of carbon- 14? * hundreds of years thousands of years million of years billion of years

11. (1 point) A reaction where a heavier nucleus splits into smaller nuclei is called ___________. * a chemical reaction background radiation fission fusion

12. (1 point) __________ and ___________ are used as moderators to capture neutrons in a nuclear reactor. * Cadmium and other metal Carbon and water Liquid sodium and water Plutonium and neptunium

13. (1 point) For a person working in a place where they might be exposed to radiation a _________ is routinely used to check their exposure. * film badge Geiger counter moderating rod scintillation counter

14. (1 point) Radioisotopes are used to do all of the following except __________. * analyze matter. diagnose medical problems. improve the flavor of food. treat diseases. study plant growth. Open response questions: Answer the following with complete sentences or if math is involve show the work

15. (3 point) The radioisotope radon-222 has a half-life of 3.8 days. How much of a 198.6 g sample of radon -222 would be left after approximately 23 days? ( Show your work) * Your answer

16. (3 point) How can an element be artificially transmuted? Give an example that has an element and what it is transmuted into. * Your answer

17. (4 point) Why does the mass and charge of an alpha particle make it less penetrating than a beta or gamma? Discuss both the mass and the charge(2 points each). *

Following are some Parent - Daughter isotope pairs with their half life:

U-238 going to Pb-206 (T_1/2 = 4.5 x 10⁹ years)

U-235 going to Pb-207 (T_1/2 = 0.7 x 10⁹ years)

C-14 going to N-14 (T_1/2 = 5700 years)

Q-1: If the C-14 : N-14 ratio in a shell in a sandstone was found to be 1 : 3, how old is the shell?

Answer-1: _____________ years

Q-2: If the U-235:Pb-207 ratio in a rock from Massachussets was determined to be 1 : 15, how old is the rock?

Answer-2: __________years

Q-3: (a) If the U-238:Pb-206 ratio in a crystal of zircon found in a sandstone was determined to be 1 : 7, what radiometric age will this give for the zircon?

Answer-3: ___________years.

(b) Does the determined age realistic? If no why not? If yes, how? (Explain briefly).

Answer-4: ________________________.

Link to online Periodic Table: https://www.ptable.com/

Three main types of decay processes involve:

1. Alpha decay: nucleus spontaneously emits an Î± (alpha) particle, same as Helium nuclei, which is 2 p+ and 2 n.

Result: atomic number decreases by 2 (lost 2 p+); atomic mass decreases by 4 (lost 2 p+ and 2n = 4 amu)

2. Beta decay: neutron in nucleus spontaneously emits a Î² (beta) particle , which is essentially an electron trapped in a neutron. The neutron, therefore, turns itself into a proton.

Result: atomic number increases by 1 (gained 1 p+); atomic mass stays same.

3. Beta or electron capture: : proton in nucleus captures a Î² (beta) particle which is essentially an electron that can become part of a neutron. The proton, therefore, turns itself into a neutron.

Result: atomic number decreases by 1 (lost 1 p+); atomic mass stays same.

For example: Po-206 (atomic number = 84) with Î± decay makes Pb-202 (atomic number = 82)

Based on the above information, complete the following radioactive transformations ( You may need to refer to a periodic table): Please write your responses as "element symbol" followed by "atomic mass" as written in this problem itself, e.g. Boron (atomic number 5 and atomic mass 11) is written as B-11.

Be-9 + Î± = (1 point)

C-12 + 2 Î± = (1 point)

Bi-206 = _________ + Î² (Note: Î² on the product side means decay from Bi) (1 point)

Tl-202 + Î² = ________ (Note:Î² on the reactant side means nucleus captured a beta particle) (1 point)

Pu-244 = ________ + 2Î± + 2Î² (Note: there are two types of particle decaying twice) (2 point)

01:160:159 Lecture 21: chap21notes

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