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This is a€?The Structure of Atomsa€?, chapter 6 from the book Principles of General Chemistry (v. This content was accessible as of December 29, 2012, and it was downloaded then by Andy Schmitz in an effort to preserve the availability of this book. PDF copies of this book were generated using Prince, a great tool for making PDFs out of HTML and CSS. For more information on the source of this book, or why it is available for free, please see the project's home page.
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Chapter 1 "Introduction to Chemistry" through Chapter 5 "Energy Changes in Chemical Reactions" introduced you to a wide variety of chemical substances and some of the most fundamental concepts in chemistry, including general descriptions of chemical bonding, mass relationships in chemical equations, and the energy changes associated with chemical reactions.
In this chapter, we describe how electrons are arranged in atoms and how the spatial arrangements of electrons are related to their energies. After reading this chapter, you will know enough about the theory of the electronic structure of atoms to explain what causes the characteristic colors of neon signs, how laser beams are created, and why gemstones and fireworks have such brilliant colors. Scientists discovered much of what we know about the structure of the atom by observing the interaction of atoms with various forms of radiant, or transmitted, energy, such as the energy associated with the visible light we detect with our eyes, the infrared radiation we feel as heat, the ultraviolet light that causes sunburn, and the x-rays that produce images of our teeth or bones. When a drop of water falls onto a smooth water surface, it generates a set of waves that travel outward in a circular direction.
Water waves are slow compared to sound waves, which can travel through solids, liquids, and gases. Water waves transmit energy through space by the periodic oscillation of matter (the water). All forms of electromagnetic radiation consist of perpendicular oscillating electric and magnetic fields. Because the various kinds of electromagnetic radiation all have the same speed (c), they differ in only wavelength and frequency. For example, the frequency of radio waves is about 108 Hz, whereas the frequency of gamma rays is about 1020 Hz. Whereas visible light is essentially harmless to our skin, ultraviolet light, with wavelengths of a‰¤ 400 nm, has enough energy to cause severe damage to our skin in the form of sunburn. The energy of electromagnetic radiation increases with increasing frequency and decreasing wavelength.
Substitute the value for the speed of light in meters per second into Equation 6.2 to calculate the wavelength in meters. As the police officer was writing up your speeding ticket, she mentioned that she was using a state-of-the-art radar gun operating at 35.5 GHz. A basic knowledge of the electronic structure of atoms requires an understanding of the properties of waves and electromagnetic radiation. Understanding the electronic structure of atoms requires an understanding of the properties of waves and electromagnetic radiation. At constant wavelength, what effect does increasing the frequency of a wave have on its speed? List the following forms of electromagnetic radiation in order of increasing wavelength: x-rays, radio waves, infrared waves, microwaves, ultraviolet waves, visible waves, and gamma rays. A large industry is centered on developing skin-care products, such as suntan lotions and cosmetics, that cannot be penetrated by ultraviolet radiation. The human eye is sensitive to what fraction of the electromagnetic spectrum, assuming a typical spectral range of 104 to 1020 Hz?
By the late 19th century, many physicists thought their discipline was well on the way to explaining most natural phenomena. One phenomenon that seemed to contradict the theories of classical physics was blackbody radiationElectromagnetic radiation whose wavelength and color depends on the temperature of the object., the energy emitted by an object when it is heated. When heated, all objects emit electromagnetic radiation whose wavelength (and color) depends on the temperature of the object. At relatively low temperatures, most radiation is emitted at wavelengths longer than 700 nm, which is in the infrared portion of the spectrum. In addition to being a physicist, Planck was a gifted pianist, who at one time considered music as a career. As the frequency of electromagnetic radiation increases, the magnitude of the associated quantum of radiant energy increases.
At the time he proposed his radical hypothesis, Planck could not explain why energies should be quantized. Only five years after he proposed it, Plancka€™s quantization hypothesis was used to explain a second phenomenon that conflicted with the accepted laws of classical physics. Albert Einstein (1879a€“1955; Nobel Prize in Physics, 1921) quickly realized that Plancka€™s hypothesis about the quantization of radiant energy could also explain the photoelectric effect. When a metal is struck by light with energy above the threshold energy Eo, the number of emitted electrons is proportional to the intensity of the light beam, which corresponds to the number of photons per square centimeter, but the kinetic energy of the emitted electrons is proportional to the frequency of the light. Plancka€™s and Einsteina€™s postulate that energy is quantized is in many ways similar to Daltona€™s description of atoms. Recently, scientists have theorized that even our sense of smell has its basis in quantum physics.
B Multiply the energy of a single photon by Avogadroa€™s number to obtain the energy in a mole of photons. B To calculate the energy in a mole of photons, we multiply the energy of a single photon by the number of photons in a mole (Avogadroa€™s number).
This energy is of the same magnitude as some of the enthalpies of reaction in Chapter 5 "Energy Changes in Chemical Reactions", and, as you will see in Chapter 8 "Ionic versus Covalent Bonding", it is comparable to the strength of many chemical bonds. An x-ray generator, such as those used in hospitals, emits radiation with a wavelength of 1.544 A…. How many times more energetic is a single x-ray photon of this wavelength than a photon emitted by a ruby laser? The properties of blackbody radiation, the radiation emitted by hot objects, could not be explained with classical physics. If electromagnetic radiation with a continuous range of frequencies above the threshold frequency of a metal is allowed to strike a metal surface, is the kinetic energy of the ejected electrons continuous or quantized? Which of the following exhibit quantized behavior: a human voice, the speed of a car, a harp, the colors of light, automobile tire sizes, waves from a speedboat?
The energy of a photon is directly proportional to the frequency of the electromagnetic radiation. Use the data in Table 6.1 "Common Wavelength Units for Electromagnetic Radiation" to calculate how much more energetic a single gamma-ray photon is than a radio-wave photon. Use the data in Table 6.1 "Common Wavelength Units for Electromagnetic Radiation" to calculate how much more energetic a single x-ray photon is than a photon of ultraviolet light.
A radio station has a transmitter that broadcasts at a frequency of 100.7 MHz with a power output of 50 kW. The photoelectric effect provided indisputable evidence for the existence of the photon and thus the particle-like behavior of electromagnetic radiation.
Although objects at high temperature emit a continuous spectrum of electromagnetic radiation (Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits"), a different kind of spectrum is observed when pure samples of individual elements are heated.


See the license for more details, but that basically means you can share this book as long as you credit the author (but see below), don't make money from it, and do make it available to everyone else under the same terms.
However, the publisher has asked for the customary Creative Commons attribution to the original publisher, authors, title, and book URI to be removed. You learned that the atoms of each element contain a unique number of positively charged protons in the nucleus and that a neutral atom has the same number of electrons as protons. Helium, neon, argon, krypton, and xenon, all monatomic elements, are five of the six known noble gases. We also explain how knowing the arrangement of electrons in an atom enables chemists to predict and explain the chemistry of an element. In contrast, energy that is transmitted, or radiated, through space in the form of periodic oscillations of electric and magnetic fields is known as electromagnetic radiationEnergy that is transmitted, or radiated, through space in the form of periodic oscillations of electric and magnetic fields. The visible portion of the electromagnetic spectrum is the narrow region with wavelengths between about 400 and 700 nm.
Because the ozone layer described in Chapter 3 "Chemical Reactions" absorbs sunlight with wavelengths less than 350 nm, it protects us from the damaging effects of highly energetic ultraviolet radiation. You will discover why scientists had to rethink their classical understanding of the nature of electromagnetic energy, which clearly distinguished between the particulate behavior of matter and the wavelike nature of energy. If we came from the planet Krypton and had x-ray vision (i.e., if our eyes were sensitive to x-rays in addition to visible light), how would this fraction be changed? Given the following characteristic wavelengths for each species, identify the spectral region (ultraviolet, visible, etc.) in which the following line spectra will occur. They could calculate the motions of material objects using Newtona€™s laws of classical mechanics, and they could describe the properties of radiant energy using mathematical relationships known as Maxwella€™s equations, developed in 1873 by James Clerk Maxwell, a Scottish physicist. The wavelength of energy emitted by an object depends on only its temperature, not its surface or composition. A relatively low-temperature object, such as an electric stove element, on a low setting appears red, whereas a higher-temperature object, such as the filament of an incandescent light bulb, appears yellow or white. A plot of the intensity of blackbody radiation as a function of wavelength for an object at various temperatures is shown in Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits".
The dull red glow of the electric stove element in Figure 6.5 "Blackbody Radiation" is due to the small amount of radiation emitted at wavelengths less than 700 nm, which the eye can detect.
During the 1930s, Planck felt it was his duty to remain in Germany, despite his open opposition to the policies of the Nazi government. By assuming that energy can be emitted by an object only in integral multiples of hI?, Planck devised an equation that fit the experimental data shown in Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits".
Initially, his hypothesis explained only one set of experimental dataa€”blackbody radiation.
When certain metals are exposed to light, electrons are ejected from their surface (Figure 6.7 "The Photoelectric Effect"). Thus Einstein showed that the energy of the emitted electrons depended on the frequency of the light, contrary to the prediction of classical physics. He was born in Germany and throughout his childhood his parents and teachers had worried that he might be developmentally disabled. Both theories are based on the existence of simple building blocks, atoms in one case and quanta of energy in the other. Preliminary research indicates that odorant molecules absorb a quantum of energy that causes their bonds to vibrate at a specific frequency. When used for commercial applications, such lasers are generally designed to emit radiation over a narrow range of wavelengths to reduce their cost. Max Planck postulated that energy was quantized and could be emitted or absorbed only in integral multiples of a small unit of energy, known as a quantum. The concept of the photon, however, emerged from experimentation with thermal radiation, electromagnetic radiation emitted as the result of a sourcea€™s temperature, which produces a continuous spectrum of energies. For example, when a high-voltage electrical discharge is passed through a sample of hydrogen gas at low pressure, the resulting individual isolated hydrogen atoms caused by the dissociation of H2 emit a red light. A few moments later the journalist asks Goku if they all plan on fighting in the Cell Games.
Satan goes on to suggest that they have no idea how much power they’re going up against.
I didn’t wanna waste time noting each and every time his name is changed or removed all together.
You may also download a PDF copy of this book (147 MB) or just this chapter (8 MB), suitable for printing or most e-readers, or a .zip file containing this book's HTML files (for use in a web browser offline). You also learned that protons and neutrons constitute most of the mass of the atom and that electrons occupy most of the volume of an atom. When atoms of these gases are excited by the flow of electrons in the discharge tubes, they emit photons of visible light in their characteristic spectral colors. As you study the material presented in this chapter, you will discover how the shape of the periodic table reflects the electronic arrangements of elements.
You will discover that knowing how to use the periodic table is the single most important skill you can acquire to understand the incredible chemical diversity of the elements.
We begin our discussion of the development of our current atomic model by describing the properties of waves and the various forms of electromagnetic radiation. Anyone who has visited a beach or dropped a stone into a puddle has observed waves traveling through water (Figure 6.1 "A Wave in Water").
If two waves have the same frequency and speed, the one with the greater amplitude has the higher energy. Within this range, the eye perceives radiation of different wavelengths (or frequencies) as light of different colors, ranging from red to violet in order of decreasing wavelength. Given 1.00 mol of each compound and the wavelength of absorbed or emitted light, how much energy does this correspond to? Water, with its polar molecules, absorbs electromagnetic radiation primarily in the infrared portion of the spectrum. The universe appeared to be a simple and orderly place, containing matter, which consisted of particles that had mass and whose location and motion could be accurately described, and electromagnetic radiation, which was viewed as having no mass and whose exact position in space could not be fixed.
Hence an electric stove burner or the filament of a space heater glows dull red or orange when heated, whereas the much hotter tungsten wire in an incandescent light bulb gives off a yellowish light (Figure 6.5 "Blackbody Radiation"). One of the major assumptions of classical physics was that energy increased or decreased in a smooth, continuous manner. As the temperature of the object increases, the maximum intensity shifts to shorter wavelengths, successively resulting in orange, yellow, and finally white light.
One of his sons was executed in 1944 for his part in an unsuccessful attempt to assassinate Hitler, and bombing during the last weeks of World War II destroyed Plancka€™s home.
Similarly, musical instruments like a piano or a trumpet can produce only certain musical notes, such as C or F sharp. We can understand Plancka€™s explanation of the ultraviolet catastrophe qualitatively as follows: At low temperatures, radiation with only relatively low frequencies is emitted, corresponding to low-energy quanta. If quantization were observed for a large number of different phenomena, then quantization would become a law (as defined in Chapter 1 "Introduction to Chemistry").
Classical physics predicted that the number of electrons emitted and their kinetic energy should depend on only the intensity of the light, not its frequency.


When light strikes the metal cathode, electrons are emitted and attracted to the anode, resulting in a flow of electrical current.
Einstein postulated that each metal has a particular electrostatic attraction for its electrons that must be overcome before an electron can be emitted from its surface (Eo = hI?o).
The patent office job was a low-level civil service position that was not very demanding, but it did allow Einstein to spend a great deal of time reading and thinking about physics.
The work of Planck and Einstein thus suggested a connection between the quantized nature of energy and the properties of individual atoms.
Because different assemblages of molecules have different characteristic frequencies, these vibrations seem to act as a molecular signature that can be detected as an odor.
In fact, an entire area of chemistry called photochemistry is devoted to studying such processes. The energy of a quantum is proportional to the frequency of the radiation; the proportionality constant h is a fundamental constant (Plancka€™s constant).
More direct evidence was needed to verify the quantized nature of electromagnetic radiation. Unlike blackbody radiation, the color of the light emitted by the hydrogen atoms does not depend greatly on the temperature of the gas in the tube. After showing off by breaking 14 roofing tiles and telling Cell that’s gonna be him soon, the journalist shouts some more nonsense. These facts do not, however, explain the stoichiometries and the structures of chemical compounds; a deeper understanding of the electronic structure of atoms is required. All noble gases have the maximum number of electrons possible in their outer shell (2 for helium, 8 for all others), so they do not form chemical compounds easily. In this and subsequent chapters, we build on this information to explain why certain chemical changes occur and others do not.
These waves are produced when wind, a stone, or some other disturbance, such as a passing boat, transfers energy to the water, causing the surface to oscillate up and down as the energy travels outward from its point of origin. Some forms of electromagnetic radiation are shown in Figure 6.4 "The Electromagnetic Spectrum". The components of white lighta€”a mixture of all the frequencies of visible lighta€”can be separated by a prism, as shown in part (b) in Figure 6.4 "The Electromagnetic Spectrum". For example, classical physics predicted that as wavelength decreased, the intensity of the radiation an object emits should increase in a smooth curve without limit at all temperatures, as shown by the broken line for 6000 K in Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits".
At high temperatures, all wavelengths of visible light are emitted with approximately equal intensities. Because these instruments cannot produce a continuous range of frequencies, their frequencies are quantized. As the temperature of an object increases, there is an increased probability of emitting radiation with higher frequencies, corresponding to higher-energy quanta. In fact, however, each metal was found to have a characteristic threshold frequency of light; below that frequency, no electrons are emitted regardless of the lighta€™s intensity. If the incoming light is interrupted by, for example, a passing person, the current drops to zero.
If photons of light with energy less than Eo strike a metal surface, no single photon has enough energy to eject an electron, so no electrons are emitted regardless of the intensity of the light. In 1905, he published his paper on the photoelectric effect, for which he received the Nobel Prize in 1921. In fact, Einsteina€™s Nobel Prize was awarded for his work on the photoelectric effect (not for his more famous equation E = mc2), demonstrating its fundamental importance. Studies with flies show that they can distinguish between similar molecules with different vibrational frequencies. In the phenomenon of photosynthesis, green plants use the energy of visible light to convert carbon dioxide and water into sugars such as glucose.
Albert Einstein used Plancka€™s concept of the quantization of energy to explain the photoelectric effect, the ejection of electrons from certain metals when exposed to light. In this section, we describe how experimentation with visible light provided this evidence. As a wave passes a particular point on the surface of the water, anything floating there moves up and down.
A similar phenomenon creates a rainbow, where water droplets suspended in the air act as tiny prisms. Soon, however, scientists began to look more closely at a few inconvenient phenomena that could not be explained by the theories available at the time.
Thus classical physics could not explain the sharp decrease in the intensity of radiation emitted at shorter wavelengths (primarily in the ultraviolet region of the spectrum), which we now refer to as the a€?ultraviolet catastrophe.a€? In 1900, however, the German physicist Max Planck (1858a€“1947) explained the ultraviolet catastrophe by proposing that the energy of electromagnetic waves is quantized rather than continuous. The white light spectrum shown for an object at 6000 K closely approximates the spectrum of light emitted by the sun (Figure 6.14 "The Visible Spectrum of Sunlight").
At any temperature, however, it is simply more probable for an object to lose energy by emitting n lower-energy quanta than a single very high-energy quantum that corresponds to ultraviolet radiation.
Above the threshold frequency, the number of electrons emitted was found to be proportional to the intensity of the light, and their kinetic energy was proportional to the frequency. This vibrational theory of smell could serve as a discriminatory process in nature in other ways and is an active area of research. Einstein postulated the existence of what today we call photons, particles of light with a particular energy, E = hI?.
Satan is shocked that they don’t know who he is and begins yelling to Krillin reiterating who he is. Electromagnetic radiation consists of two perpendicular waves, one electric and one magnetic, propagating at the speed of light (c). This means that for each temperature, there is a maximum intensity of radiation that is emitted in a blackbody object, corresponding to the peaks in Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits", so the intensity does not follow a smooth curve as the temperature increases, as predicted by classical physics. Note the sharp decrease in the intensity of radiation emitted at wavelengths below 400 nm, which constituted the ultraviolet catastrophe. The result is a maximum in the plot of intensity of emitted radiation versus wavelength, as shown in Figure 6.6 "Relationship between the Temperature of an Object and the Spectrum of Blackbody Radiation It Emits", and a shift in the position of the maximum to lower wavelength (higher frequency) with increasing temperature.
This phenomenon was called the photoelectric effectA phenomenon in which electrons are ejected from the surface of a metal that has been exposed to light..
The energy of violet light is above the threshold frequency, so the number of emitted photons is proportional to the lighta€™s intensity. Electromagnetic radiation is radiant energy that includes radio waves, microwaves, visible light, x-rays, and gamma rays, which differ only in their frequencies and wavelengths. Thus energy could be gained or lost only in integral multiples of some smallest unit of energy, a quantumThe smallest possible unit of energy.
The classical prediction fails to fit the experimental curves entirely and does not have a maximum intensity. As you can see in Figure 6.2 "Important Properties of Waves", two waves can have the same amplitude but different wavelengths and vice versa.



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