TOPIC: Radioactivity & Natural Transmuations

Do Now: Where on your reference table can you find radioactive particles?

Not all isotopes are stable

Stable isotopes have…

1:1 ratio of n0 to p+ (for elements <20)

1.5:1 ratio of n0 to p+ (for elements >20)

Beyond Element 83 are very unstable (radioactive)

• No amount neutrons can hold nucleus together once it has 83+ protons

• All Elements 83 and above on PT are radioactive

• Other elements may have radioactive isotopes applet

Radioisotopes- unstable nucleus – they are radioactive

the nucleus of element emits subatomic particles and/or electromagnetic waves…by emitting these particles,nucleus changes into different element (it’s trying to become more stable)

Radioactive Decay Series

• Sometimes 1 transmutation isn’t enough to achieve stability

• Some radioisotopes go through several changes before they achieve stability (and are no longer radioactive)

U-238 PB-206

Transmutation-When an element turns into a different element. This occurs when the number of protons changes.

These subatomic particles that are emitted were discovered around 1900 • Alpha rays• Beta rays• Gamma rays

Radioactivity – Rutherford again!

Penetration & Shielding

2 Neutrons & 2 Protons

Charge = +2Mass = 4amu

42He

Beta Particle – fast moving electronBeta Particle – fast moving electron

Transmutation

• 2 types–Natural–Artificial

Natural Transmutation

Happens all by itself (spontaneous)Happens all by itself (spontaneous)

Not affected by Not affected by anythinganything in environment in environment

• 1 term on reactant side• Original isotope

• 2 terms on product side• Emitted Particle • New Isotope

Natural Transmutation

16N 0e + 16O7 -1 8

1 term on reactant side

2 terms on product side

Balancing Nuclear Equations

16N 0e + 16O7 -1 8

Conservation of mass number: 16 = 0 + 16

Conservation of atomic number: 7 = -1 + 8

232Th 4He + X9090 22

Conservation of Mass Number:Conservation of Mass Number:

sum of mass numbers on left side must = sum of mass numbers on left side must = sum of mass numbers on right sidesum of mass numbers on right side

YY

Z

232 = 4 + Y so Y = 228

232Th 4He + 228X9090 22

Conservation of Atomic Number:Conservation of Atomic Number:

sum of atomic numbers on left side must = sum of atomic numbers on left side must = sum of atomic numbers on right sidesum of atomic numbers on right side

ZZ

90 = 2 + Z so Z = 88