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Chapter 5 Electrons In Atoms.

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Presentation on theme: "Chapter 5 Electrons In Atoms."— Presentation transcript:

1 Chapter 5 Electrons In Atoms

2 Topics to Be Covered 5.1 5.2 5.3 Light and Quantized Energy 136-145
Quantum Theory and the Atom 5.3 Electron Configuration

3 Light and Quantized Energy
Section 5.1 Light and Quantized Energy

4 The Atom & Unanswered Questions
Early 1900s Discovered 3 subatomic particles Continued quest to understand atomic structure Rutherford’s model Positive charge in nucleus Fast moving electrons around that No accounting for differences and similarities in chemical behavior

5 The Atom and Unanswered Questions
Example: Lithium, sodium, and potassium have similar chemical behaviors (explained more in next chapter) Early 1900s Scientists began to unravel mystery Certain elements emitted visible light when heated in a flame Analysis revealed chemical behavior depends on arrangement of electrons

6 The Wave Nature of Light
Electromagnetic radiation A form of energy that exhibits wavelike behavior as it travels through space Visible light is a type of ER

7 Characteristics of Waves
All waves can be described by several characteristics Wavelength Frequency Amplitude

8 Wavelength Represented by lambda λ
Shortest distance between equivalent points on a continuous waves Measure crest to crest or trough to trough Usually expressed in m, cm, or nm

9 Frequency Represented by nu ν
The number of waves that pass a given point per second Given in the unit of hertz (Hz) 1 Hz = 1 wave per second

10 Amplitude The wave’s height from the origin to a crest or from the origin to a trough Wavelength and frequency do not affect amplitude

11 Speed All electromagnetic waves in a vacuum travel at a speed of 3.00 x 108 m/s This includes visible light The speed of light has its own symbol C C= λν

12 Electromagnetic Spectrum
Also called the EM spectrum Includes all forms of electromagnetic radiation With the only differences in the types of radiation being their frequencies and wavelengths

13 Electromagnetic Spectrum
Figure 5.5

14 Problems Page 140 Calculating Wavelength of an EM Wave

15 Particle Nature of Light
Needed to explain other properties of light Heated objects emit only certain frequencies of light at a given temperature Some metals emit electrons when light of a specific frequency shines on them

16 Quantum Concept When objects are heated they emit glowing light 1900
Max Planck began searching for an explanation Studied the light emitted by heated objects Startling conclusion

17 Quantum Concept Planck discovered:
Matter can gain or lose energy only in small specific amounts These amounts are called quanta Quantum—is the minimum amount of energy that can be gained or lost by an atom

18 Example Heating a cup of water
Most people thought that you can add any amount of thermal energy to the water by regulating the power and duration of the microwaves In actuality, the temperature increases in infinitesimal steps as its molecules absorb quanta of energy, which appear to be a continuous manner

19 Quantum Concept Planck proposed that energy emitted by hot objects was quantized Planck further demonstrated mathematically that a relationship exists between energy of a quantum and a frequency

20 Energy of a Quantum Equantum=hv Equantum represents energy
h is Planck’s constant v represents frequency

21 Planck’s Constant Symbol = h 6.626 x 10-34 J*s
J is the symbol for joule The SI unit of energy The equation shows that the energy of radiation increases as the radiation’s frequency, v, increases.

22 Planck’s Theory For given frequencies
Matter can emit/absorb energy only in whole number multiples of hv 1hv, 2hv, 3hv, 4hv etc. Matter can have only certain amounts of energy Quantities of energy between these values do not exist

23 The Photoelectric Effect
electrons, called photoelectrons are emitted from a metal’s surface when light of a certain frequency, or higher than a certain frequency shines on the surface

24 Light’s Dual Nature Einstein proposed in 1905 that light has a dual nature photon—a massless particle that carries a quantum of energy

25 Energy of a Photon Ephoton=hv Ephoton represents energy
h is Planck’s constant v represents frequency

26 Light’s Dual Nature Einstein proposed
Energy of a photon must have a certain threshold value to cause the ejection of a photoelectron from the surface of a metal Even small #s of photons with energy above the threshold value will cause the photoelectric effect Einstein won Nobel Prize in Physics in 1921

27 Sample Problems Page 143 Sample Problem 5.2
Calculating Energy of a Photon

28 Atomic Emission Spectra
See page 145

29 Quantum Theory and The Atom
Section 5.2 Quantum Theory and The Atom

30 Bohr’s Model of the Atom
Dual-nature explains more Atomic Emission Spectra Not continuous Only certain frequencies of light Explained the Atomic Emission Spectra

31 Energy States of Hydrogen
Bohr proposed certain allowable energy states Bohr proposed electrons could travel in certain orbitals

32 Energy states of Hydrogen
Ground State Lowest allowable energy state of an atom Orbit size Smaller the orbit, the lower the energy state/level Larger the orbit, the higher the energy state/level

33 Energy states of Hydrogen
Hydrogen can have many excited states It only has one electron Quantum Number Number assigned to each orbital n Look at Table 5.1

34 The Hydrogen Line Spectrum
Hydrogen Ground State Electron is in n=1 orbit Does not radiate energy Hydrogen Excited State Energy is added to the atom from outside source Electron moves to a higher energy orbit

35 The Hydrogen Line Spectrum
Only Certain Atomic Energy Levels Possible Example Our Classroom Balmer Series Electron transitions from higher-energy orbits to the second orbit Account for visible lines

36 The Hydrogen Line Spectrum
Lyman Series Ultraviolet Electrons drop into n=1 orbit Paschen Series Infrared Electrons drop into n = 3 orbit

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