1. Atomic Structure Structure of the Nuclear Atom
Prentice-Hall Chapter 4.2
Dr. Yager

2. Objectives Identify three types of sub-atomic particles.
Describe the structure of atoms according to the Rutherford atomic model.

3. The Three Sub-Atomic Particles
Electrons
Protons
Neutrons

4. After the Dalton Atomic Theory
In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron.
Electrons are negatively charged subatomic particles.

5. J. J. Thomson
At Work in His Lab
Cathode Ray Tube

6. Cathode Ray Tube

7. A cathode ray is deflected by a magnet.

8. A cathode ray is deflected by electrically charged plates.

9. Thomson’s Particles
He called the particles “corpuscles” and they were later named electrons.
He measured the ratio of charge to the mass.
The results did not depend on materials used.
Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements.

10. Robert Millikan 1868-1953 Measured the charge on the electron
Used his famous oil drop experiment

11. Proton
In 1886, Eugene Goldstein (1850–1930) observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles.
Such positively charged subatomic particles are called protons.

12. J.J. Thomson and others supposed the atom was filled with positively charged material and the electrons were evenly distributed throughout.
Plum-Pudding Model
Negatively-charged electrons (raisins) uniformly distributed through the positively-charged pudding.

13. The plum pudding model of the atom was short-lived, however, due to the work of Ernest Rutherford (1871–1937).
Ernest Rutherford’s Portrait

14. Rutherford’s Gold-Foil Experiment

15. Alpha Particle
Helium nucleus: 2 protons, 2 neutrons

16. What happens when an alpha particle (+ charge) approaches a nucleus (+ charge)

17. Alpha particles scatter from the gold foil.

18. What Rutherford Concluded
Atoms are mostly empty space
All positive charge and most of the mass is concentrated in a small region (nucleus)

19. Neutron
In 1932, the English physicist James Chadwick (1891–1974) confirmed the existence of yet another subatomic particle: the neutron.
Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton.

20. Properties of Electrons, Protons and Neutrons

21. 1. Which of the following is NOT an example of a subatomic particle?
proton
molecule
electron
neutron

22. 1. Which of the following is NOT an example of a subatomic particle?
proton
molecule
electron
neutron

23. 2. The nucleus of an atom consists of
electrons only.
protons only.
protons and neutrons.
electrons and neutrons.

24. 2. The nucleus of an atom consists of
electrons only.
protons only.
protons and neutrons.
electrons and neutrons.

25. 3. Most of the volume of the atom is occupied by the
electrons.
neutrons.
protons and neutrons.
protons.

26. 3. Most of the volume of the atom is occupied by the
electrons.
neutrons.
protons and neutrons.
protons.

27. 3. Most of the mass of the atom is occupied by the
electrons.
neutrons.
protons and neutrons.
protons.

28. 3. Most of the mass of the atom is occupied by the
electrons.
neutrons.
protons and neutrons.
protons.