Alpha-Particle Scattering and Rutherford's Nuclear Model of the Atom
Ernest Rutherford's alpha-particle scattering experiment (conducted by Hans Geiger and Ernest
Marsden in 1909) led to the nuclear model of the atom,
which revolutionized our understanding of atomic structure. Below is a full explanation of the
experiment, its observations, and the conclusions that led to Rutherford's model.
1. The Alpha-Particle Scattering Experiment
Experimental Setup:
- A thin gold foil (~100 nm thick) was bombarded with alpha particles (helium nuclei, He^2+).
- A fluorescent screen coated with zinc sulfide was placed around the foil to detect scattered alpha
particles.
- The scattering angles of the alpha particles were observed using a microscope.
2. Observations from the Experiment
1. Most of the alpha particles passed straight through the gold foil without any deviation.
2. Some alpha particles were slightly deflected at small angles.
3. A few alpha particles (about 1 in 8000) bounced back at angles greater than 90 degrees, with
some even deflecting close to 180 degrees.
3. Conclusions from the Observations
From these results, Rutherford concluded:
1. Most of the atom is empty space -> Since most alpha particles passed through undeflected.
2. The atom has a small, dense, positively charged nucleus -> Since some alpha particles were
deflected, there must be a region with a strong positive charge.
3. The nucleus contains most of the atom's mass -> Since a small fraction of alpha particles
bounced back, they must have hit something massive.
4. Electrons orbit the nucleus -> Since the atom is mostly empty space and remains electrically
neutral.
4. Rutherford's Nuclear Model of the Atom
Based on these conclusions, Rutherford proposed a new atomic model:
1. The atom consists of a central nucleus that is small, dense, and positively charged.
2. Electrons revolve around the nucleus in orbits (like planets around the sun).
3. The size of the nucleus is very small compared to the overall size of the atom (about 1/100,000 of
the atomic diameter).
4. The positive charge of the nucleus balances the negative charge of electrons, making the atom
Ernest Rutherford's alpha-particle scattering experiment (conducted by Hans Geiger and Ernest
Marsden in 1909) led to the nuclear model of the atom,
which revolutionized our understanding of atomic structure. Below is a full explanation of the
experiment, its observations, and the conclusions that led to Rutherford's model.
1. The Alpha-Particle Scattering Experiment
Experimental Setup:
- A thin gold foil (~100 nm thick) was bombarded with alpha particles (helium nuclei, He^2+).
- A fluorescent screen coated with zinc sulfide was placed around the foil to detect scattered alpha
particles.
- The scattering angles of the alpha particles were observed using a microscope.
2. Observations from the Experiment
1. Most of the alpha particles passed straight through the gold foil without any deviation.
2. Some alpha particles were slightly deflected at small angles.
3. A few alpha particles (about 1 in 8000) bounced back at angles greater than 90 degrees, with
some even deflecting close to 180 degrees.
3. Conclusions from the Observations
From these results, Rutherford concluded:
1. Most of the atom is empty space -> Since most alpha particles passed through undeflected.
2. The atom has a small, dense, positively charged nucleus -> Since some alpha particles were
deflected, there must be a region with a strong positive charge.
3. The nucleus contains most of the atom's mass -> Since a small fraction of alpha particles
bounced back, they must have hit something massive.
4. Electrons orbit the nucleus -> Since the atom is mostly empty space and remains electrically
neutral.
4. Rutherford's Nuclear Model of the Atom
Based on these conclusions, Rutherford proposed a new atomic model:
1. The atom consists of a central nucleus that is small, dense, and positively charged.
2. Electrons revolve around the nucleus in orbits (like planets around the sun).
3. The size of the nucleus is very small compared to the overall size of the atom (about 1/100,000 of
the atomic diameter).
4. The positive charge of the nucleus balances the negative charge of electrons, making the atom
