Section 1 The Nucleus Section 2 Nuclear Decay Section 3 ...

[Pages:64]Subatomic Physics

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Section 1 The Nucleus Section 2 Nuclear Decay Section 3 Nuclear Reactions Section 4 Particle Physics

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Section 1

Subatomic Physics

Section 1

TEKS

The student is expected to:

5A research and describe the historical development of the concepts of gravitational, electromagnetic, weak nuclear, and strong nuclear forces 5H describe evidence for and effects of the strong and weak nuclear forces in nature 8C describe the significance of mass-energy equivalence and apply it in explanations of phenomena such as nuclear stability, fission, and fusion

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Subatomic Physics

Section 1

What do you think?

? What holds a nucleus together?

? What particles exist within the nucleus? ? What force(s) exist between these particles? ? Are these forces attractive or repulsive?

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Subatomic Physics

Section 1

The Nucleus

? The chemical symbol for an element is written like the one shown to the left. What information is provided by this symbol?

? The atomic number (Z) or number of protons is 13.

? The mass number (A) or number of protons + neutrons is 27.

? The number of neutrons (N) is 14 (27 ? 13).

? The element is aluminum.

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Subatomic Physics

Section 1

Isotopes

? Isotopes are atoms of the same element with different atomic masses.

? The number of neutrons is different.

? Most carbon nuclei have 6 protons and 6 neutrons and an atomic mass of 12.

? Called carbon-12 ? Others have 5 neutrons (carbon-11), 7 neutrons

(carbon-13), or 8 neutrons (carbon-14).

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Subatomic Physics

Isotopes

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Visual Concept

Section 1

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Subatomic Physics

Section 1

Nuclear Mass

? The density of the nucleus is approximately 2.3 ? 1017 kg/m3.

? Mass is measured in unified mass units (u).

? 1 u is one-twelfth the mass of one atom of carbon-12.

? 1 u = 1.6605 ? 10-27 kg

? Protons and neutrons each have a mass of approximately 1 u.

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Subatomic Physics

Nuclear Mass

Section 1

? Find the energy equivalent of 1 u in both J and eV.

(For c, use the value 2.9979 ? 108 m/s.) ? Answers:

? 1.4924 ? 10-44 J, 931.47 ? 106 eV or 931.47 MeV

? With more significant figures, 1 u = 931.49 MeV. ? The mass of subatomic particles is often expressed in

MeV.

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