A Brief History of the Atom & Atomic Models

1. A Brief History of the Atom & Atomic Models

2. Democritus • 480 B.C. a • Greek philosopher • Theorized everything was made out of tiny particles – atoms • Believed that atoms were hard, solid spheres that could not be destroyed • Idea was controversial - had no evidence - no one believed him.

3. Democritus • “The good things of life are produced by learning with hard work; the bad are reaped of their own accord, without hard work." • "Fame and wealth without intelligence are dangerous possessions."

4. John Dalton • English school teacher • Formed his own atomic theory. • Elements made of tiny particles -atoms. • Atoms cannot be created or divided into smaller particles. • Atoms of a an element are different from those of any other element.

5. John Dalton • Had evidence to support his idea - Democritus did not. • Viewed the atom as a hard, solid spheres - could not be broken down. • This theory was disproved by the discovery of electrons

6. J.J. Thompson • Discovered electron by using the cathode ray tube. • Cathode rays were stream of (-) charged particles.

7. J.J. Thompson • Model had (+) and (-) charges scattered throughout the atom. • Known as chocolate chip cookie model. • This model was disproven by discovery of the nucleus. Plum Pudding model

8. Ernest Rutherford • Discovered nucleus by the Gold Foil Experiment. • Angles of deflection that alpha particles (+) made proved evidence of a nucleus.

9. Ernest Rutherford • Model defines location and charge of nucleus – doesn’t clearly define location of the electrons. • This model is IMPROVED by the Bohr model.

10. Niels Bohr • Model depicts atom as small, (+) charged nucleus surrounded by electronsin orbit. • Similar to the solar system, but with forces providing attraction, rather than gravity.

12. Bohr’s model • This model states that an electrons occupy specific positions around the nucleus. • He stated that the electrons are confined to these orbits. • They can “jump” to another orbit only if some form of energy is given to that electron

13. Particles or Waves? • Bohr’s model was found to be slightly inaccurate. • The idea of an electron actually flying around in little circles turned out to have lots of problems • Electrons have both particle and wave properties.

14. Wave-Particle Duality Theory • Einstein theorized that light and matter exhibit properties of both waves and of particles. • This theory helps explain the idea that electrons have characteristics of waves and particles. • In order to better understand the atomic structure, it is helpful to understand waves and the nature of light • All waves can be described by several characteristics.

15. Waves • Some characteristics of waves are wavelength, frequency, amplitude and speed. • Wavelength (λ) is the shortest distance between equivalent points on a continuous wave. • Amplitude is the height of the wave from the origin to the crest or the origin to the trough.

16. Waves • Frequency (ν) is the number of waves that pass a given point per second. It is measured in hertz (Hz) • Frequency is expressed as “waves per second,” (1/s) or (s-1) • 652 Hz = 652 waves/second = 652 s-1

17. Frequency and Wavelength • Frequency and wavelength are inversely related • As the wavelength increases, frequency decreases • Frequency is an indication of energy. • Which wave has the greatest wavelength? • The greatest frequency? 3 2

18. Waves • All electromagnetic waves travel at the same speed of 3.00 x 108 m/s • The speed of light (c) is the product of its wavelength (λ) and frequency (ν). c = λ ν • Because all light moves at the same speed, it is possible to identify the wavelength or frequency of any wave.

19. Example • What is the wavelength of a wave with a frequency of 5.00 x 1012 Hz ? c = λ ν c = 3.00 x 108 m/s ν = 5.00 x 1012 Hz 3.00 x 108 m/s = ( λ ) (5.00 x 1012s-1) λ = 3.00 x 108 5.00 x 1012λ = 6.00 x 10-5 m

20. More Examples • What is the frequency of a wave having a wavelength of 3.33 x 10-8 m? • What is the speed of a wave with a frequency of 1.33 x 1017 Hz and a wavelength of 2.25 x 109 m? • What is the wavelength of a wave having a frequency of 7.6 x 106 Hz? 9.01 x 1015 Hz 3.00 x 108 m/s 39.5 m

21. Wave Nature of Light • Light is a type of electromagnetic radiation. • Electromagnetic radiation is a form of energy that exhibits wavelike behavior at it travels through space. • Different types of electromagnetic radiation are distinguished by their wavelengths • Visible light from the sun, microwaves that cook our food, X rays that doctors use, and waves that carry radio and T.V. programs are all forms of electromagnetic radiation.

22. Visible Light • We are familiar with all the colors of visible light from our everyday experiences. • If you have ever seen a rainbow, you have seen all the visible colors at once. • The various colors that we see correspond to specific wavelength and frequency • White light, a form of visible light, contains a continuous range of wavelengths and frequencies.

23. White Light • When sun light, one example of white light, passes through a prism it is separated into a continuous spectrum of colors. • The spectrum is called continuous because all portions of light correspond to a unique wavelength and frequency.

24. The Visible Light Spectrum • What color has the greatest wavelength? • What color has the greatest energy?

25. Electromagnetic Spectrum • Visible light is one part of the electromagnetic spectrum. • EM spectrum encompasses all forms of electromagnetic radiation ordered by their wavelength and frequencies. • EM spectrum contains radio and TV waves, Microwaves, infrared rays, ultraviolet rays, X rays, and gamma rays.

26. Electromagnetic Spectrum

27. Electromagnetic Spectrum • Which type of EM radiation are the highest in energy? • Which type has the highest wavelength? • Which has a higher frequency X rays or Infrared rays?

28. Homework • Pg. 25 in your study guide • Pg. 126 in your book Section 5.1 Assessment #12