Descriptive Inorganic Chemistry (eBook)

James E. House, Kathleen A. House (Autoren)

eBook Download: PDF | EPUB

2015 | 3. Auflage
440 Seiten
Elsevier Science (Verlag)
978-0-12-802979-4 (ISBN)

Infos

House's Descriptive Inorganic Chemistry, Third Edition, provides thoroughly updated coverage of the synthesis, reactions, and properties of elements and inorganic compounds. Ideal for the one-semester (ACS-recommended) sophomore or junior level course in descriptive inorganic chemistry, this resource offers a readable and engaging survey of the broad spectrum of topics that deal with the preparation, properties, and use of inorganic materials. Using rich graphics to enhance content and maximize learning, the book covers the chemical behavior of the elements, acid-base chemistry, coordination chemistry, organometallic compounds, and numerous other topics to provide a coherent treatment of the field. The book pays special attention to key subjects such as chemical bonding and Buckminster Fullerenes, and includes new and expanded coverage of active areas of research, such as bioinorganic chemistry, green chemistry, redox chemistry, nanostructures, and more. - Highlights the Earth's crust as the source of most inorganic compounds and explains the transformations of those compounds into useful products - Provides a coherent treatment of the field, covering the chemical behavior of the elements, acid-base chemistry, coordination chemistry, and organometallic compounds - Connects key topics to real world industrial applications, such as in the area of nanostructures - Includes expanded coverage on bioinorganic chemistry, green chemistry, redox chemistry, superacids, catalysis, and other areas of recent development

J.E. House is Scholar in Residence, Illinois Wesleyan University, and Emeritus Professor of Chemistry, Illinois State University. He received BS and MA degrees from Southern Illinois University and the PhD from the University of Illinois, Urbana. In his 32 years at Illinois State, he taught a variety of courses in inorganic and physical chemistry. He has authored almost 150 publications in chemistry journals, many dealing with reactions in solid materials, as well as books on chemical kinetics, quantum mechanics, and inorganic chemistry. He was elected Professor of the Year in 2011 by the student body at Illinois Wesleyan University. He has also been elected to the Southern Illinois University Chemistry Alumni Hall of Fame. He is the Series Editor for Elsevier's Developments in Physical & Theoretical Chemistry series, and a member of the editorial board of The Chemical Educator.

Textauszug

Chapter 2

Atomic Structure and Properties

Abstract

From the results of experiments involving light and line spectra, Bohr developed a model of the hydrogen atom that correctly predicted the positions of spectral lines. Following the work of de Broglie that indicated the wave character of a moving particle and the quantized nature of energy by Planck, Schrödinger solved the problem of the hydrogen atom by wave mechanics, thus ushering in modern quantum mechanical procedures. Solution of the hydrogen atom problem led to the requirement for quantum numbers. Electrons in an atom each have a unique set of four quantum numbers, and no two electrons can have identical sets (Pauli exclusion principle). The arrangement of electrons in atoms gives rise to difference in properties which in turn result in differences in chemical behavior.

Keywords

Atomic properties; Atomic structure; Electronegativity; Electron affinity; Electronic configuration; Hydrogen-like orbitals; Ionization energy; Quantum number

The fundamental unit involved in elements and the formation of compounds is the atom. Properties of atoms such as the energy necessary to remove an electron (ionization potential), energy of attraction for additional electrons (electron affinity), and atomic sizes are important factors that determine the chemical behavior of elements. Also, the arrangement of electrons in atoms has a great deal of influence on the types of molecules the atoms can form. Because descriptive inorganic chemistry is the study of chemical reactions and properties of molecules, it is appropriate to begin that study by presenting an overview of the essentials of atomic structure.

The structure of atoms is based on the fundamental principles described in courses such as atomic physics and quantum mechanics. In a book of this type, it is not possible to present more than a cursory description of the results obtained by experimental and theoretical studies on atomic structure. Consequently, what follows is a nonmathematical treatment of the aspects of atomic structure that provides an adequate basis for understanding much of the chemistry presented later in this book. Much of this chapter should be a review of principles learned in earlier chemistry courses, which is intentional. More theoretical treatments of these topics can be found in the suggested readings at the end of this chapter.

2.1. Atomic Structure

A knowledge of the structure of atoms provides the basis for understanding how they combine and the type of bonds that are formed. In this section, a review of early work in this area will be presented and variations in atomic properties will be related to the periodic table.

2.1.1. Quantum Numbers

It was the analysis of the line spectrum of hydrogen observed by J. J. Balmer and others that led Niels Bohr to a treatment of the hydrogen atom that is now referred to as the Bohr model. In that model, there are supposedly “allowed” orbits in which the electron can move around the nucleus without radiating electromagnetic energy. The orbits are those for which the angular momentum, mvr, can have only certain values (they are referred to as being quantized). This condition can be represented by the relationship

vr=nh2π

(2.1)

where n is an integer (1, 2, 3,…) corresponding to the orbit, h is Planck's constant, m is the mass of the electron, v is its velocity, and r is the radius of the orbit. Although the Bohr model gave a successful interpretation of the line spectrum of hydrogen, it did not explain the spectral properties of species other than hydrogen and ions containing a single electron (He+, Li2+, etc.).

In 1924, Louis de Broglie, as a young doctoral student, investigated some of the consequences of relativity theory. It was known that for electromagnetic radiation, the energy, E, is expressed by the Planck relationship,

=hυ=hcλ

(2.2)

where c, v, and λ are the velocity, frequency, and wavelength of the radiation, respectively. The photon also has an energy given by a relationship obtained from relativity theory,

=mc2

(2.3)

A specific photon can have only one energy so the right-hand sides of Eqs (2.2) and (2.3) must be equal. Therefore,

cλ=mc2

(2.4)

and solving for the wavelength gives

=hmc

(2.5)

The product of mass and velocity equals momentum so the wavelength of a photon, represented by h/mc, is Planck's constant divided by its momentum. Because particles have many of the characteristics of photons, de Broglie reasoned that for a particle moving at a velocity, v, there should be an associated wavelength that is expressed as

=hmv

(2.6)

This predicted wave character was verified in 1927 by C. J. Davisson and L. H. Germer who studied the diffraction of an electron beam that was directed at a nickel crystal. Diffraction is a characteristic of waves so it was demonstrated that moving electrons have a wave character.

If an electron behaves as a wave as it moves in a hydrogen atom, a stable orbit can result only when the circumference of a circular orbit contains a whole number of waves. In that way, the waves can join smoothly to produce a standing wave with the circumference being equal to an integral number of wavelengths. This equality can be represented as

πr=nλ

(2.7)

where n is an integer. Because λ is equal to h/mv, substitution of this value in Eq. (2.7) gives

πr=nhmv

(2.8)

which can be rearranged to give

vr=nh2π

(2.9)

It should be noted that this relationship is identical to Bohr's assumption about stable orbits (shown in Eq. (2.1))!

In 1926, Erwin Schrödinger made use of the wave character of the electron and adapted a previously known equation for three-dimensional waves to the hydrogen atom problem. The result is known as the Schrödinger wave equation for the hydrogen atom which can be written as

2Ψ+2mℏ2(E−V)Ψ=0

(2.10)

where Ψ is the wave function, ħ is h/2π, m is the mass of the electron, E is the total energy, V is the potential energy (in this case the electrostatic energy) of the system, and ∇2 is the Laplacian operator.

2=∂2∂x2+∂2∂y2+∂2∂z2

(2.11)

The wave function is, therefore, a function of the coordinates of the parts of the system that completely describes the system. A useful characteristic of the quantum mechanical way of treating problems is that once the wave function is known, it provides a way for calculating some properties of the system.

The Schrödinger equation for the hydrogen atom is a second-order partial differential equation in three variables. A customary technique for solving this type of differential equation is by a procedure known as the separation of variables. In that way, a complicated equation that contains multiple variables is reduced to multiple equations, each of which contains a smaller number of variables. The potential energy, V, is a function of the distance of the electron from the nucleus, and this distance is represented in Cartesian coordinates as r = (x2 + y2 + z2)1/2. Because of this relationship, it is impossible to use the separation of variables technique. Schrödinger solved the wave equation by first transforming the Laplacian operator into polar coordinates. The resulting equation can be written as

r2∂∂rr2∂Ψ∂r+1r2sinθ∂∂θ(sinθ∂Ψ∂θ)+1r2sin2θ∂2Ψ∂ϕ2+2mℏ2(E+e2r)Ψ=0

(2.12)

Although no attempt will be made to solve this very complicated equation, it should be pointed out that in this form the separation of the variables is possible, and equations that are functions of r, θ, and ϕ result. Each of the simpler equations that are obtained can be solved to give solutions that are functions of only one variable. These partial solutions are described by the functions R(r), Θ(θ), and Φ(ϕ), respectively, and the overall solution is the product of these partial solutions.

Figure 2.1 Illustrations of the possible ml values for cases where l = 1 (a) and l = 2 (b).

It is important to note at this point that the mathematical restrictions imposed by solving the differential equations naturally lead to some restraints on the nature of the solutions. For example, solution of the equation containing r requires the introduction of an integer,...

Produkt-Details

• Erscheint lt. Verlag: 10.9.2015
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Anorganische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Organische Chemie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Technik
• ISBN-10: 0-12-802979-X / 012802979X
• ISBN-13: 978-0-12-802979-4 / 9780128029794