Chapter 5 Electrons In Atoms

Topics to Be Covered 5.1 5.2 5.3 Light and Quantized Energy 136-145 Quantum Theory and the Atom 146-155 5.3 Electron Configuration 156-162

Light and Quantized Energy Section 5.1 Light and Quantized Energy

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

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

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

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

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

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

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

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

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

Electromagnetic Spectrum Figure 5.5

Problems Page 140 Calculating Wavelength of an EM Wave

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

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

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

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

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

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

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.

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

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

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

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

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

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

Atomic Emission Spectra See page 145

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

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

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

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

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

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

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

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