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Waves & Particles Ch. 4 - Electrons in Atoms.

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Presentation on theme: "Waves & Particles Ch. 4 - Electrons in Atoms."— Presentation transcript:

1 Waves & Particles Ch. 4 - Electrons in Atoms

2 Properties of Light Different types of electromagnetic radiation (x-rays, radio waves, microwaves, etc…) SEEM to be very different from one another. Yet they share certain fundamental characteristics. 3.0 x 108 m/sec is the speed of light!

3 A. Wavelength Wavelength – distance between identical points on successive waves Usually measured in nanometers

4 B. Frequency Frequency – the number of complete wave cycles that pass a given point in one second: the unit is cycles/second but is written as sec-1, or Hertz. One wave in one second equals one Hertz!

5 Amplitude Amplitude is the height of a wave. It is also measured in length units like nanometers, angstroms, etc.

6  A A  A. Waves greater amplitude crest (intensity) origin trough
greater frequency (color)

7 c = f EM Spectrum c: speed of light (3.00  108 m/s)
Frequency & wavelength are inversely proportional c = f c: speed of light (3.00  108 m/s) : wavelength (m, nm, etc.) f: frequency (Hz)

8 EM Spectrum c = f Longer Wavelength means Lower Frequency
Shorter Wavelength means Higher Frequency Higher Frequency means Higher Energy Lower Frequency means Lower Energy

9 Range The range of visible light is from 400 to 700 nanometers. Low energy is colored red while high energy is colored violet. Violet:   nm Indigo:   nm Blue:   nm Green:   nm Yellow:   nm Orange:   nm Red:   nm

10 Ephoton = hf E : engery of a photon (J)
h: Plank’s constant (6.63 x J . sec) f: frequency (Hz or sec-1)


12 EM Spectrum HIGH ENERGY LOW ENERGY R O Y G. B I V red orange yellow
green blue indigo violet

13 Examples 2. What is the wavelength of radiation whose frequency is 6.24 x l013 sec-1? Given: Work: f = 6.24 x l013 Hz c = 3.00  108 m/s λ = ? λ = c/f λ = 3.00  108 6.24 x l013

14 Answer 4.81 x 10-6 m

15 Examples 3. What is the frequency of radiation whose wavelength is 2.20 x l0-6 nm? (1 m = 1,000,000,000 nm) Given: Work: c = 3.00  108 m/s λ = 2.20 x 10-6 nm (you have to change nm to m) f = ? f = c/ λ f = 3.00  108 2.20 x 10-15

16 Answer 1.36 x 1023 Hz

17 Hydrogen Atom Line Emission Spectra
When investigators passed electric current through a vacuum tube containing hydrogen gas at low pressure, they observed the emission of a characteristic pinkish glow. When a narrow beam of the emitted light was shined through a prism, it was separated into a series of specific frequencies (and therefore specific wavelengths, c =) of visible light. The bands of light were part of what is known as hydrogen’s LINE-EMISSION SPECTRUM. (page 95)

18 The lowest energy state of an atom is its ground state.
A state in which an atom has a higher amount of energy is an excited state. When an excited atom returns to its ground state, it gives off energy.

19 B. Bohr Model e- exist only in orbits with specific amounts of energy called energy levels Therefore… e- can only gain or lose certain amounts of energy only certain photons are produced

20 B. Bohr Model 6 Energy of photon depends on the difference in energy levels Bohr’s calculated energies matched the IR, visible, and UV lines for the H atom 5 4 3 2 1

21 C. Other Elements Helium
Each element has a unique bright-line emission spectrum. “Atomic Fingerprint” Helium Bohr’s calculations only worked for hydrogen! 

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