Chapter 19

Question 1

Notation for Symbolizing Isotopes

Answer 1

^A_ZX

A = Mass number (sum of the number of protons and number of neutrons in the nucleus)

Z = Atomic number (# of protons in nucleus)

X = Chemical Symbol

⇒The number of neutrons in the nucleus: (N) = A - Z

Question 2

Nuclide

Answer 2

A particular isotope of an atom.

Question 3

Alpha Decay

Answer 3

Occurs when an unstable nucleous emits a particle composed of two protons and two neutrons.

α Particle: ⁴₂He

Question 4

Nuclear Equation

Answer 4

²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He

• The sum of the atomic numbers on both sides of a nuclear equation must be equal.
• The sum of the mass numbers on both sides must be equal.
  *

Question 5

Ionizing Power

Answer 5

The ability of radiation to ionize other molecules and atoms.

Question 6

Penetrating Power

Answer 6

The ability to penetrate matter.

Question 7

Beta Decay

Answer 7

Occurs when an unstable nucleus emits an electron.

Neutron → proton + emitted electron

β particle: ⁰_-1e

²²⁸₈₈Ra → ²²⁸₈₉Ac + ⁰_-1e

Question 8

Gamma Ray Emission

Answer 8

A form of electromagnetic radiation.

Question 9

Gamma Ray

Answer 9

• High-energy (short-wavelength) photons
• γ ray: ⁰₀y
• Has no charge or mass

Question 10

Positron

Answer 10

The antiparticle of the electron: it has the same mass as an electron, but the opposite charge.

Positron: ⁰₊₁e

Question 11

Positron Emission

Answer 11

Occurs when an unstable nucleus emits a positron.

Proton → neutron + emitted positron

³⁰₁₅P → ³⁰₁₄Si + ⁰₊₁e

Question 12

Electron Capture

Answer 12

Occurs when a nucleus assimilates an electron from an inner orbital of its electron cloud.

Proton + electron → neutron

⁹²₄₄Ru + ⁰_-1e → ⁹²₄₃Tc

Question 13

Strong Force

Answer 13

Strongest of the four fundamental forces of physics but acts over the shortest distance.

Responsible for holding the protons and neutrons together in the nucleus of an atom.

Question 14

N/Z Ratio

Answer 14

• Ratio of neutrons to protons: N/Z
• N/Z too high: Nuclides that lie above the valley of stability have too many neutrons and tend to convert neutrons to protons via beta decay.
• N/Z too low: Nuclides that lie below the valley of stability have too many protons and tend to convert protons to neutrons via positron emission or electron capture.

Question 15

Magic Numbers

Answer 15

Certain numbers of nucleons that confer unique stability.

N or Z = 2, 8, 20, 28, 50, 82, and N = 126

Question 16

Radiocarbon Dating

Answer 16

A form of radiometric dating based on the C-14 isotope.

Question 17

Radiometric Dating

Answer 17

A technique used to estimate the age of rocks, fossils, or artifacts that depends on the presence of radioactive isotopes and their predictable decay with time.

Question 18

Nuclear Fission

Answer 18

The splitting of the uranium atom.

Question 19

Mass Defect

Answer 19

The difference in mass between the nucleus of an atom and the sum of the separated particles that make up that nucleus.

Question 20

Nuclear Binding Energy

Answer 20

The amount of energy required to break apart the nucleus into its component nucleons.

Question 21

Relationship between mass units and energy units

Answer 21

1 amu = 931.5 MeV

Question 22

Nuclear Fusion

Answer 22

The combination of two light nuclei to form a heavier one.

Question 23

Transmutation

Answer 23

The transformation of one element into another as a result of nuclear reactions.

Question 24

First-Order Rate Law

Answer 24

Rate = kN

N = number of radioactive nuclei

k = rate constant

Question 25

Half-Life

Answer 25

The time required for the concentration of a reactant
or the amount of a radioactive isotope to fall to one-half of its initial
value.

t_1/2 = 0.693/k

Question 26

What is the heat of fission of 1 mole of ²³⁵U?

Answer 26

1.66 x 10¹⁰ kJ/mol