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The Nucleus. The nucleus of an atom contains two types of particles. Proton. Neutron. These particles can be attracted to each other by the nuclear force. A chemical element is defined by the number of protons. Hydrogen. Helium. Lithium. But the charges pose a problem…. Helium.

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but the charges pose a problem
But the charges pose a problem…

Helium

The positive charges of the protons prevent the nuclear force from keeping them together.

but the charges pose a problem1
But the charges pose a problem…

Helium

The neutral charge of the neutron allows more than one proton to be present.

isotopes are elements that have forms with different atomic masses
Isotopes are elements that have forms with different atomic masses.

Lithium – 7 (%92.5 of all lithium)

Lithium – 6 (%7.5 of all lithium)

the average atomic mass periodic table is a weighted average of all the isotopes of that element
The average atomic mass (periodic table) is a weighted average of all the isotopes of that element

Average = (7Li atomic mass x abundance)

+(6Li atomic mass x abundance)

Weighted average atomic mass

Average = (7 x %92.5)

+(6 x %7.5)

6.9

3

6.9

Li

some isotopes have too many or not enough neutrons and are unstable
Some isotopes have too many or not enough neutrons and are unstable

Carbon - 12

Carbon - 13

Carbon - 14

slide11
Some nuclei become so unstable that they release energy (radioactive)This happens in one of three ways…

Alpha Decay – Nucleus releases 2p+and 2n0

Beta Decay – Nucleus releases 1e- and a n0becomes a p+

Gamma Decay – Nucleus releases a gamma ray (energy)

Images from wikipedia

radioactive decay
Radioactive Decay

6 p+

8 n0

14C

Neutron

Proton

7 p+

7 n0

14N

Electron

different types of radiation require different levels of protection
Different types of radiation require different levels of protection

Sheet of paper

Sheet of aluminum

Thick layer of lead

Images from wikipedia

decay and half life
Decay and Half-Life
  • Nuclei decay in a very predictable way.
  • Half-Life: The time it takes for one half of the sample to decay.
  • If you had 100 atoms of Carbon-14, it would take 5730 years for 50 of them to become Nitrogen-14.
  • If you had 1,000,000 atoms of C-14, it would take 5730 years for 500,000 of them to become N-14.
decay and half life1
Decay and Half-Life

25 atoms of 14C

50 atoms of 14C

100 atoms of 14C

12-13 atoms of 14C

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3(5730 years) = 17910 years

2(5730 years) = 11460 years

5730 years

slide16
A fission reaction is where a very heavy nucleus (U, Pu) is split to release two small nuclei, neutrons, and a great deal of energy

Ba-141

Kr-92

U-235

neutrons

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