how radioactivity was discovered

Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel, who is pictured 1.1. Becquerel was experimenting with uranium, which was known to glow after being exposed to sunlight. Becquerel wanted to see if the glow was caused by rays of energy, like rays of light or X-rays. He placed a bit of uranium on a photographic plate after exposing the uranium to sunlight. The plate was similar to the film that is used today to take X-rays, and Becquerel expected the uranium to leave an image on the plate. The next day, there was an image on the plate, just as Becquerel expected. This meant that uranium gives off rays after being exposed to sunlight. Becquerel was a good scientist, so he wanted to repeat his experiment to confirm his results. He placed more uranium on another photographic plate. However, the day had turned cloudy, so he tucked the plate and uranium in a drawer to try again another day. He wasnt expecting the uranium to leave an image on the plate without first being exposed to sunlight. To his surprise, there was an image on the plate in the drawer the next day. Becquerel had discovered that uranium gives off rays of energy on its own. He had discovered radioactivity, for which he received a Nobel prize. Another scientist, who worked with Becquerel, actually came up with the term radioactivity. The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries.


radioactive elements

Radioactivity is the ability of an atom to emit, or give off, charged particles and energy from its nucleus. The charged particles and energy are called by the general term radiation. Only unstable nuclei emit radiation. They are unstable because they have too much energy, too many protons, or an unstable ratio of protons to neutrons. For example, all elements with more than 83 protonssuch as uranium, radium, and poloniumhave unstable nuclei. They are called radioactive elements. The nuclei of these elements must lose protons to become more stable. When they do, they become different elements.

elements and protons

For an atom of one element to change into a different element, the number of protons in its nucleus must change. Thats because each element has a unique number of protons. For example, lead atoms always have 82 protons, and gold atoms always have 79 protons. Q: So how can one element change into another? A: The starting element must be radioactive, and its nuclei must gain or lose protons.

instructional diagrams

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certain chemical processes can change one element into another.

a. true

-->  b. false

atoms of each element have a unique number of

-->  a) protons.

b) neutrons.

c) isotopes.

d) two of the above

all nuclei emit radiation.

a. true

-->  b. false

nuclei may be unstable if they have

a) too much energy.

b) too many protons.

c) an unstable ratio of protons to neutrons.

-->  d) any of the above

all elements with more than 75 protons are unstable.

a. true

-->  b. false

which of the following elements are radioactive?

a) uranium

b) radium

c) polonium

-->  d) all of the above

diagram questions

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