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Nuclear Forces and Quarks
Unit: Nuclear Chemistry
Knowledge/Understanding Goals:
 fundamental forces
 quarks
 how the processes of β− and β+ decay happen
The Four Fundamental Forces
strong force (or “strong nuclear force”): the force that holds the
nucleus together. The energy comes from converting the mass defect
to energy.
weak force: the force that makes protons and/or neutrons in the nucleus
unstable. This can cause changes to the nucleus which change the
element into a different one. (Yes, you could actually turn lead into
gold this way!)
electromagnetic force: the force between electrical charges. If the
charges are the same (“like charges”)—both positive or both
negative—the particles repel each other. If the charges are
different (“opposite charges”)—one positive and one negative—the
particles attract each other.
gravity: the force that causes masses to attract each other. Usually
only observable if one of the masses is very large (like a planet).
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AP Chemistry II
Copyright © 2009–2017 Mr. Bigler.
Permission is granted to copy, distribute and/or modify this document under the terms
of the GNU Free Documentation License, Version 1.3 or any later version published by
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Nuclear Forces and Quarks
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Force
Relative Strength
Strong
1
Weak
10−6
1
1
/137
∞, but gets smaller as (distance)2
10−39
∞, but gets smaller as (distance)2
Electromagnetic
Gravity
Effective Distance
Diameter of the nucleus
/3 diameter of the nucleus
Quarks
fundamental particle (or “elementary particle”): a particle that does not
appear to be made of anything smaller. (“Where have I heard that
before?”) Electrons are a fundamental particle, but protons and
neutrons are not.
quark: one of the types of fundamental particle.
Quarks come in six flavors:

 Up

Down

Top

Charm
Bottom

Strange
Protons & neutrons are made of up & down quarks. An “up” quark has a
charge of +2/3, and a “down” quark has a charge of −1/3.
proton: a subatomic particle made of two up quarks (+2/3) and one down
quark (−1/3):
↑↑ ↓
The net charge on a proton is:
2(+2/3) + (−1/3) = +1.
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AP Chemistry II
Mr. Bigler
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Nuclear Forces and Quarks
neutron: a subatomic particle made of two down quarks and one up quark:
↑↓↓
The net charge on a neutron is:
(+2/3) + 2(−1/3) = 0.
Quarks and Radioactive Decay
Beta (β) radioactive decay occurs when the weak force changes the spin
on one of the quarks in a proton or neutron. In β− decay (the more wellknown form), the spin goes from “down” to “up,” which turns a neutron
into a proton. In β+ decay, the spin goes from “up” to “down,” which turns
a proton into a neutron.
Because of the law of conservation of charges (the total charge has to be
the same before and after any change), any change that produces a
positive charge has to also produce a negative charge. The way this
happens is that when the quark changes its spin, the neutron turns into a
proton plus a particle called a “W− boson.” The W− boson then splits into
an electron and a neutral fundamental particle called a neutrino. Both the
electron and the neutrino are ejected from the nucleus of the atom at
high speed.
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AP Chemistry II
Mr. Bigler
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