Chapter 7: Quantum Theory and Atomic Structure The Nature of Light Atomic Spectra The Wave - Particle Duality of Matter and Energy The Quantum - Mechanical Model of the Atom

Chapter 7 - Quantum Theory of the Atom Read the entire chapter Answer all the Review Problems. Problems: 19, 23, 27, 31, 33, 37, 39, 43, 45, 47, 49, 51, 53, 57, 63, 65, 67, 71, 75, 77, 81,

What are the electrons doing in the atom? Why do atoms form ions and molecules? Why do hydrogen and oxygen “stick” together to form water? To understand these questions, we need to understand the electronic structure of the atom Electronic structure referes to the way the electrons are arranged in an atom

Atoms are the basic building blocks of matter. They are the smallest units of an element that can combine with other elements (that is, take part in a chemical reaction.

Structure of the Atom The simple view: only three subatomic particles have a bearing on chemical behavior. Protons, Neutrons and Electrons

Proton is a nuclear particle having a positive charge equal to that of the electron and a mass more that 1800 times that of the electrons. Neutron is a nuclear particle having a mass almost identical to that of the proton but with no electric charge Electron is a negatively charged particle with the negative charge equal to that of the proton.

Protons and neutrons reside together in a very small volume within the atom known as the nucleus. Most of the rest of the atom is space in which the electrons move

electrons neutrons protons

1. Each element is composed of extremely small particles called atoms. 2. All atoms of a given element are identical. 3. Atoms of different elements have different properties (including different masses). 4. Atoms and elements are not changed into different types of atoms by chemical reactions. 5. Compounds are formed when atoms of more than one element combine.

We Know: Atoms (elements) are the basic unit of chemical stucture and are made of protons, neutrons and electrons (simplification) Compounds are made up of elements (atoms) in difinite proportions. Compounds are also called Molecules.

C 6 12.011 Group Atomic number 14A Atomic symbol Period 2 Atomic mass (amu) Parts of the Periodic Table

The present theory of the electronic structure of the atom started with an explanation of the colored light produced in hot gases and flames This means we need to know something about the nature of light and radiant energy Radiant energy is electromagnetic radiation: light, X rays All types of radiant energy move through a vacuum at the speed of light (c) 3.00 x 108 m/s All radiant energy has wavelike characteristics

A wave is periodic in nature and can be characterized by its wavelength and frequency

l l l l is the distance between any two adjacent identical points of a wave

l Frequency (n) - the number of wavelengths of that wave that pass a fixed point in one unit of time (usually 1 sec.)

Short wavelength High Frequency Long wavelength low frequency Wavelength and frequency are related

What else do we know? We said that all types of radiant energy move through a vacuum at 3.0 x 108 m/s We know that l is the distance between identical points on successive waves We know that n is the number of times per second that one complete wavelength passes a given point. So: c = l n

The yellow light given off by a sodium lamp has a wavelength of 589 nm. What is the frequency of this radiation? c = l n n = c/ l c = 3.0 x 108 m/s n = 3.0 x 108 m/s x 109 nm = 5.09 x 1014/s 589 nm 1 m

Electromagnetic radiation (light) consists of occilations in electric and magnetic fields that can travel through space. These occilations can be characterized in terms of wavelength and frequency The range of frequencies and wavelengths of electromagnetic radiation is called the electromagnetic spectrum The visible spectrum 400 nm (violet) to 800 nm (red)

Fig. 7.3

The Spectrum of Electromagnetic Radiation The wavelength of visible light is between 400 and 700 nanometers Radio, TV , microwave and infrared radiation have longer wavelengths (shorter frequencies), and lower energies than visible light. Gamma rays and X-rays have shorter wavelengths (larger frequencies), and higher energies than visible light!

Fig. 7.1

Fig. 7.2

Electromagnetic Radiation WAVELENGTH - The distance between identical points on successive waves. (  ) FREQUENCY - The number of waves that pass through a particular point per second. () AMPLITUDE - The vertical distance from the midline to a peak, or trough in the wave. c  

Calculation of Frequency from Wavelength Problem: The wavelength of an x-ray is 1.00 x10 -9 m or 1 nm, what is the frequency of this x-ray? If the wavelength of long-wavelength electromagnetic radiation is 7.65 x 104 m, what is the frequency of this long-wavelength radiation used to contact submerged nuclear submarines at sea? Plan: Use the relationship between wavelength and frequency to obtain the answer. wavelength x frequency = speed of light! Solution: speed of light wavelength(m) frequency(cycles/sec) = 3.00 x 108 m/s 1.00 x 10 - 9 m a) frequency = = 3.00 x 1017 cycles/sec 3.00 x 108 m/s 7.65 x 104 m b) frequency = = 3.92 x 103 cycles/s

Different Behaviors of Waves and Particles Fig. 7.4

The Diffraction Pattern Caused by Light Passing through Two Adjacent Slits Fig. 7.5

The Photoelectric Effect - I Below the threshold energy, nothing occurs ! Above the threshold, the kinetic energy of the ejected electrons is proportional to the frequency of the light. Also, when above the threshold, as intensity of the light increases, so does the number of ejected electrons. All metals experience this effect, but each has a unique threshold frequency.

The Photoelectric Effect - II Albert Einstein Theorized Photons Won Nobel prize - 1921 Photons have an energy equal to: E = h h = Plank’s Constant, and is equal to: 6.6260755 x 10 - 3 4Jsec

Demonstration of the Photoelectric Effect Fig. 7.7