Radioactivity and Nuclear Reactions

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Radioactivity

When the strong force can hold a nucleus together forever, the nucleus is stable.

If not, the nucleus becomes unstable and can break apart or decay by emitting particles and energy.

Large nuclei are more unstable; all with more than 83 protons are radioactive.

Slide 22

What are isotopes?

Atoms of the same element may have different numbers of neutrons in the nucleus.

Slide 23

What are isotopes?

Atoms of the same element may have different numbers of neutrons in the nucleus.

The atoms of all isotopes of an element have the same numbers of protons & electrons & the same chemical properties.

Slide 24

What makes nuclei unstable?

The ratio of neutrons to protons determines whether a nucleus is stable or unstable.

Small isotopes 1 neutron:1 proton

Large isotope 3 neutrons: 2 protons

Generally, nuclei with too many or too few neutrons compared to the numbers are unstable or radioactive.

Slide 25

How is a nucleus described?

Atomic number= proton number

Mass number= protons + neutrons

Slide 26

How is an atom’s information shown?

Scientists use symbols to write information about atoms.

C is the symbol for carbon with 6 protons and 6 neutrons in the isotope C-12. Stable w/ 1:1 ratio

Slide 27

How is an atom’s information shown?

This isotope is carbon-14 with 6 protons and 14 -6 or 8 neutrons; the ratio is 8:6 so this is unstable or radioactive.

14

C

6

Slide 28

Who discovered radioactivity?

In 1896, Henri Becquerel accidentally left pieces of uranium salt in a drawer on a photographic plate. When he developed the plate, he saw an outline of the uranium salt on it. He realized that it must have given off rays that darkened the film.

http://www.hulu.com/watch/113908/milestones-in-science-and-engineering-radioactivity-%E2%80%93-henri-becquerel-marie-and-pierre-curie

Slide 29

Who discovered radioactivity?

Two years later Marie and Pierre Curie discovered two new elements, polonium and radium, both radioactive.

Slide 30

Who discovered radioactivity?

Two years later Marie and Pierre Curie discovered two new elements, polonium and radium, both radioactive.