Nuclear Chemistry

Nuclear Chemistry

“Bravo” Test 1954 – 15,000 kilotons

Chapter 19: Radioactivity and Nuclear EnergyObjective 12: To learn the types of radioactive decay (Section 19.1) Objective 13: To learn to write nuclear equations that describes radioactive decay (Section 19.1) Objective 14: To learn how one element may be changed into another by particle bombardment (Section 19.2)

What makes an atom radioactive?

Radioactivity: the spontaneous decomposition of a nucleus to form another nucleus and produce one or more particles. -the heavier the atom, the more likely it is to be radioactive-if the number of protons in the nucleus exceeds 83, then the nuclide is radioactive-all of the positive charge is concentrated in one area; therefore the nucleus is unstable

Types of Radioactive Decay

alpha production (a, He): helium nucleus

beta production (b, e):

gamma ray production (g):

ThHeU 23490

42

23892

234 234 090 91 1Th Pa e

g0023490

42

23892 2 ThHeU

Specifying Isotopes

5

XA

Z X = the symbol of the element

A = mass number (protons + neutrons)

Z = the atomic number (number of protons)

Nuclear Symbols

Element symbolMass number, A (p+ + no)

Atomic number, Z(number of p+)

U23592

Key to Balancing Nuclear Equations

In nuclear reactions, both the atomic number Z and the mass number A must be conserved

Balancing Nuclear Equations

226 488 2Ra a

226 = 4 + ____222

222

88 = 2 + ___86

86

Atomic number 86 is radon, Rn

Rn

Alpha DecayAlpha production

(a): an alpha particle is

ahelium nucleus238 4 234

92 2 90U He Th

Alpha decay is limited to heavy, radioactive

nuclei

238 4 23492 2 90U Tha

4 2 4 22 2He or a

Alpha (α) Decay

E1

P+N

P P-2 + He4

2 E2

P+N -4

an alpha particle (helium nucleus) is produced

Alpha Radiation

Limited to VERY large nucleii.

Example of Alpha Decay

Ra222

88 86 + He4

2 RnRadium 222 decays by α particle production to Radon

218

218

Beta DecayBeta production (b):A beta particle is an electron ejected from the nucleus

234 234 090 91 1Th Pa e

Beta emission converts a neutron to a proton

234 234 090 91 1Th Pa b

0 01 1e or b

Beta (β) Decay

Beta emission converts a neutron to a proton

E1

P+N

P P+1 + e0-1 E2

P+N

Beta Radiatio

nConverts a neutron into a proton.

Example of Beta DecayNotice the mass of the beta particle is zero; it is so small that is must be neglected.

C14

6 7 + e0-1 N14

Example of Beta Decay

Th234

90 91 + e0-1 Pa

234

Thorium 234 decays by β particle production to Protactinium 234

(notice: no change in mass number A, and an increase of 1 in atomic number Z)

Gamma Ray ProductionGamma ray production (g):

Gamma rays are high energy photons produced in association with other forms of decay.Gamma rays are massless and do not, by themselves, change the nucleus

g0023490

42

23892 2 ThHeU

Gamma Ray ProductionGamma ray production (g):

Gamma rays are high energy photons produced in association with other forms of decay.Gamma rays are massless and do not, by themselves, change the nucleus

g0023490

42

23892 2 ThHeU

Positron ProductionPositron emission:Positrons are the anti-particle of the electron

Positron emission converts a proton to a neutron

NeeNa 2210

01

2211

e01

Positron Production

E1

P+N

P P-1 + e01 E2

P+N

Positron emission converts a proton to a neutron

Electron CaptureElectron capture: (inner-orbital electron is captured by the nucleus)

Electron capture converts a proton to a neutron

g0020179

01

20180 AueHg

Alpha Particle Emission

Beta Particle Emission

Gamma Ray Emission

Symbol or or

Mass Heavy Light No Mass

How it changes the

nucleus

Decreases the mass number by 4

Decreases the atomic number by 2

Converts a neutron into a proton

Increases atomic number by 1

No change to the nucleus

Penetration Low Medium High

Protection provided by…

Skin Paper, clothing Lead

Danger Low Medium High

242He

242a e01 b01 g00

Types of Radiation

NuclearStability

Decay will occur in such a way as to return a nucleus to the band (line) of stability.The most stable nuclide is Iron-56

If Z > 83, the nuclide is radioactive

A Decay Series

A radioactive nucleus reaches a stable state by a series of steps

Graphic – Wikimedia Commons User Tosaka

Alpha Particle Emission

Beta Particle Emission

Gamma Ray Emission

Symbol or or

Mass Heavy Light No Mass

How it changes the

nucleus

Decreases the mass number by 4

Decreases the atomic number by 2

Converts a neutron into a proton

Increases atomic number by 1

No change to the nucleus

Penetration Low Medium High

Protection provided by…

Skin Paper, clothing Lead

Danger Low Medium High

242He

242a e01 b01 g00

A Decay SeriesA radioactive nucleus reaches a stable state by a series of steps

Graphic – Wikimedia Commons User Tosaka

Particle BombardmentNuclear transformation involves changing one element into another by bombarding it with small nuclei, protons, or neutrons in a particle accelerator