Nuclear ChemistryNuclear Chemistry

Nuclear Chemistry

• Remember that an element is defined by the number of protons in the nucleus.

• If I say the Oxygen-18 Isotope, I am referring to the Atomic Mass as 18.

• This can be written as 18O.

• Remember, the Atomic Mass is the number of protons and neutrons.

Nuclear Chemistry

• Many Isotopes are radioactive.

• Radioactivity is the spontaneous decomposition of nuclei.

• Spontaneous means they do it alone, with no required input of energy from us.

Alpha Decay

• Alpha particle (4He) is ejected.

• Only happens when Z > 83

• 222Ra 4He + 218Rn + (γ rays)

• The sums of nucleons is conserved!

What isotope is formed from the Alpha decay of Bi-211?

A.) Tl-207

B.) Tl-215

C.) At-207

D.) At-215

E.)

Beta Decays

• Three major types of beta decay:

– Negatron

– Positron

– Megatron (just kidding!)

– Electron Capture

Negatron Decay

• Changes a neutron into a proton

• Produces a negatron and antineutrino

• Occurs when n/p ratio is too high

• 24Na 24Mg + β- + ν-

What isotope will be formed from the negatron decay of Ag-116?

A.) Pd-117

B.) Pd-115

C.) Ag-115

D.) Cd-116

Positron Decay

• Changes a proton into a neutron

• Produces a positron, neutrino, and occasionally a gamma ray

• Occurs when n/p ratio is too low

• 45Ti 45Sc + β+ + ν + (γ rays)*

What isotope will be formed from the positron decay of Na-22?

A.) Ne-21

B.) Ne-22

C.) Mg-21

D.) Mg-22

Positronium

• When a positron is ejected from the nucleus it can encounter an electron.

• Since they have opposite charges, they attract and form Positronium (Ps).

• Lasts from 1.25 x 10-14 s to 1.1 x 10-9 s until annihilation

Annihilation

• Eventually (like really quickly) the two particles collide.

• This is the collision of a particle with its antiparticle which turns matter into energy.

• This is where the γ rays come from

Electron Capture

• Occurs when n/p ratio is too low.

• Steals an orbital electron, collides with a proton turning it into a neutron.

• 201Hg + -1e 201Ag + γ + ν + (X-Ray or Auger electron)

What isotope will be formed from the electron capture decay of As-

73?

A.) Se-74

B.) Se-73

C.) Ge-73

D.) Ge-74

Gamma Decay

• Atoms at a higher energy level can release that energy via a gamma ray.

• 110mAg 110Ag + γ

• M = metastable state, a somewhat stable equilibrium at a higher energy level.

Predicting Decay Method

• Alpha: BIG (Z>83) Atoms!

• Negatron: n/p ratio too high

• Positron: n/p ratio too low

• Gamma: Metastable state.

Predict the decay method that the Si-27 isotope undergo.

A.) Alpha

B.) Negatron

C.) Positron

D.) Gamma

Predict the decay method that the C-14 isotope undergo.

A.) Alpha

B.) Negatron

C.) Positron

D.) Gamma

Predict the decay method that the Fr-223 isotope undergo.

A.) Alpha

B.) Negatron

C.) Positron

D.) Gamma

Predict the decay method that the O-18 isotope undergo.

A.) Alpha

B.) Negatron

C.) Positron

D.) Gamma