1 Unit 2: Electrons in the Atom

2 The Beginnings of Quantum Mechanics Quantum mechanics forms the foundation of chemistry – explaining the periodic table and the behavior of the elements in chemical bonding – as well as providing the practical basis for lasers, computers, and countless other applications 2 Tro: Chemistry: A Molecular Approach, 2/e

3 The Behavior of the Very Small Electrons are incredibly small –a single speck of dust has more electrons than the number of people who have ever lived on earth Electron behavior determines much of the behavior of atoms 3 Tro: Chemistry: A Molecular Approach, 2/e

4 A Theory that Explains Electron Behavior The quantum-mechanical model explains the manner in which electrons exist and behave in atoms It helps us understand and predict the properties of atoms that are directly related to the behavior of the electrons –why some elements are metals and others are nonmetals –why some elements gain one electron when forming an anion, whereas others gain two –why some elements are very reactive while others are practically inert –and other periodic patterns we see in the properties of the elements 4 Tro: Chemistry: A Molecular Approach, 2/e

5 The Nature of Light: Its Wave Nature Light is a form of electromagnetic radiation All electromagnetic waves move through space at the same, constant speed 5 Tro: Chemistry: A Molecular Approach, 2/e

6 Speed of Energy Transmission 6 Tro: Chemistry: A Molecular Approach, 2/e

7 Characterizing Waves The amplitude is the height of the wave –the distance from node to crest »or node to trough –the amplitude is a measure of how intense the light is – the larger the amplitude, the brighter the light The wavelength ( ) is a measure of the distance covered by the wave –the distance from one crest to the next, or trough to trough Crest – top of the wave Trough – bottom of the wave Node – midpoint of the wave

8 Characterizing Waves The frequency ( ) is the number of waves that pass a point in a given period of time –the number of waves = number of cycles –units are hertz (Hz) or cycles/s = s −1 »1 Hz = 1 s −1 The total energy is related to the amplitude of the waves and the frequency –the larger the amplitude, the more energy a wave has –the more frequently the waves strike, the more total force there is, the more energy 8 Tro: Chemistry: A Molecular Approach, 2/e

9 The Relationship Between Wavelength and Frequency For waves traveling at the same speed, the shorter the wavelength, the more frequently they pass 9 Tro: Chemistry: A Molecular Approach, 2/e λ = Wavelength. Units of meters.λ = Wavelength. Units of meters. ν = frequency. Units of hertz (Hz) or 1/sec.ν = frequency. Units of hertz (Hz) or 1/sec. c= speed of light constant. 3.0 x 108 m/sc= speed of light constant. 3.0 x 108 m/s λ = Wavelength. Units of meters.λ = Wavelength. Units of meters. ν = frequency. Units of hertz (Hz) or 1/sec.ν = frequency. Units of hertz (Hz) or 1/sec. c= speed of light constant. 3.0 x 108 m/sc= speed of light constant. 3.0 x 108 m/s

10 Example: The wavelength of a red light is 5.00 x meters. What is the frequency?

11 Color The color of light is determined by its wavelength –or frequency White light is a mixture of all the colors of visible light –a spectrum –RedOrangeYellowGreenBlueViolet 11 Tro: Chemistry: A Molecular Approach, 2/e

12 Amplitude & Wavelength 12 Tro: Chemistry: A Molecular Approach, 2/e

13 The Electromagnetic Spectrum Electromagnetic spectrum- all electromagnetic radiation, arranged according to increasing wavelength. 13 Tro: Chemistry: A Molecular Approach, 2/e

14 Thermal Imaging using Infrared Light 14 Tro: Chemistry: A Molecular Approach, 2/e

15 Sunburns Caused by High-Energy UV Radiation 15 Tro: Chemistry: A Molecular Approach, 2/e

16 Using High-Energy Radiation to Kill Cancer Cells 16 Tro: Chemistry: A Molecular Approach, 2/e

17 Facts about Electromagnetic Radiation The size of a radio wavelength (crest to crest) is approximately the length of a football field. The size of a gamma ray wavelength is approximately the size of a nucleus of an atom. X-rays have enough energy to damage human cells which is why lead vests are worn. The visible part of the spectrum is the only part that can be seen with the human eye. However, other animals can see parts of the spectrum that humans can’t. For example, a large number of insects can see ultraviolet (UV) light. Gamma rays are given off by stars, and by some radioactive substances. Lead or concrete is needed in order to block them out.

18 Energy and Frequency relationship E= energy. Units of J h= Planck’s constant (6.626x J. s). This number does not change. v= frequency. Units of Hz or 1/sec.

19 Example: A photon of light has a frequency of 1.1 x Hz. What is the energy of this photon?

20 Practice – Order the following types of electromagnetic radiation: microwaves, gamma rays, green light, red light, ultraviolet light By wavelength (short to long)By wavelength (short to long) By frequency (low to high)By frequency (low to high) By energy (least to most)By energy (least to most) gamma < UV < green < red < microwaves microwaves < red < green < UV < gamma 20 Tro: Chemistry: A Molecular Approach, 2/e

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22 Photoelectric Effect Is the emission of electrons by certain metals when light shines on them

23 Energy Excited Atom Lower Energy State Atom Photon of Red Light is Emitted

24 Light is Emitted. WHY? As energy is applied, the atom leaves a lower energy state (called the ground state) and reaches a higher energy state (called the excited state). As the atom looses energy, it will return to the ground state. As it returns to the ground state, a photon of light is emitted and observed.

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26 Review: Which type of energy on the spectrum has the greatest energy? Which type of energy on the spectrum has the largest wavelength? Which type of VISIBLE energy (ROYGBIV) has the largest wavelength? Which type of energy on the spectrum has the smallest frequency?

27 The End !!!!!!!!!!!!!!!!!!!