Page 19 - Utah Science Textbook
P. 19
Science Can Be a Blast!! Rutherford Finds the Nucleus
A physicist from New Zealand named Ernest Rutherford made
Bohr’s idea of energy the next major discovery about atoms. He discovered the nucleus.
levels is still useful today. You can watch a video about Rutherford and his discovery at this
It helps explain how URL:
matter behaves. For http://www.youtube.com/watch?v=wzALbzTdnc8 (3:28).
example, when
chemicals in fireworks Rutherford's Gold Foil Experiments
explode, their atoms In 1899, Rutherford discovered that some elements give off
absorb energy. Some of positively charged particles. He named them alpha particles ().
their electrons jump to a In 1911, he used alpha particles to study atoms. He aimed a beam of alpha particles at a
higher energy level. When very thin sheet of gold foil. Outside the foil, he placed a screen of material that glowed
the electrons move back when alpha particles struck it.
to their original energy
level, they give off the
energy as light. Different
chemicals have different
arrangements of
electrons, so they give
off light of different
colors. This explains the
blue- and purple-colored
fireworks below.
If Thomson’s plum pudding model were correct, the alpha particles should be deflected a
little as they passed through the foil. Why? The positive "pudding" part of gold atoms
would slightly repel the positive alpha particles. This would cause the alpha particles to
change course. But Rutherford got a surprise. Most of the alpha particles passed straight
through the foil as though they were moving through empty space. Even more surprising,
a few of the alpha particles bounced back from the foil as though they had struck a wall.
This is called back scattering. It happened only in very small areas at the centers of the
gold atoms.
The Nucleus and Its Particles
Based on his results, Rutherford concluded that all the positive charge of an atom is
concentrated in a small central area. He called this area the nucleus. Rutherford later
discovered that the nucleus contains positively charged particles. He named the positive
particles protons. Rutherford also predicted the existence of neutrons in the nucleus.
However, he failed to find them. One of his students, a physicist named James Chadwick,
went on to discover neutrons in 1932. You learn how at this URL:
http://www.light-science.com/chadwick.html.
20
A physicist from New Zealand named Ernest Rutherford made
Bohr’s idea of energy the next major discovery about atoms. He discovered the nucleus.
levels is still useful today. You can watch a video about Rutherford and his discovery at this
It helps explain how URL:
matter behaves. For http://www.youtube.com/watch?v=wzALbzTdnc8 (3:28).
example, when
chemicals in fireworks Rutherford's Gold Foil Experiments
explode, their atoms In 1899, Rutherford discovered that some elements give off
absorb energy. Some of positively charged particles. He named them alpha particles ().
their electrons jump to a In 1911, he used alpha particles to study atoms. He aimed a beam of alpha particles at a
higher energy level. When very thin sheet of gold foil. Outside the foil, he placed a screen of material that glowed
the electrons move back when alpha particles struck it.
to their original energy
level, they give off the
energy as light. Different
chemicals have different
arrangements of
electrons, so they give
off light of different
colors. This explains the
blue- and purple-colored
fireworks below.
If Thomson’s plum pudding model were correct, the alpha particles should be deflected a
little as they passed through the foil. Why? The positive "pudding" part of gold atoms
would slightly repel the positive alpha particles. This would cause the alpha particles to
change course. But Rutherford got a surprise. Most of the alpha particles passed straight
through the foil as though they were moving through empty space. Even more surprising,
a few of the alpha particles bounced back from the foil as though they had struck a wall.
This is called back scattering. It happened only in very small areas at the centers of the
gold atoms.
The Nucleus and Its Particles
Based on his results, Rutherford concluded that all the positive charge of an atom is
concentrated in a small central area. He called this area the nucleus. Rutherford later
discovered that the nucleus contains positively charged particles. He named the positive
particles protons. Rutherford also predicted the existence of neutrons in the nucleus.
However, he failed to find them. One of his students, a physicist named James Chadwick,
went on to discover neutrons in 1932. You learn how at this URL:
http://www.light-science.com/chadwick.html.
20
