How Electrons Form Atoms

Elements and Compounds—Chemical Symbols—Molecules—Atoms —Electrons—How Electrons Form Atoms—Explanation of Chemical Activity—Chemical Formulas—Speed of Chemical Reactions—Physical and Chemical Changes—The Law of Definite Proportions—Different Kinds of Chemical Reaction —Classification of Chemical Compounds—The Law of Combining Weights—Solutions—Acids and Bases—Neutral Substances—Organic and Inorganic Chemistry—Electrochemistry —Experiments in Electrochemistry, Pages 7-39... 

We now know that electrons in atoms can hold only particular energies and that their probable whereabouts are described by Schrodiiiger s wave function. The energies and probable locations depend on integer numbers, or quantum numbers. Quantum numbers describe the energy and geometry of the possible electronic states of an atom. These states, in turn, deteriiiilie the chemical behavior of the elements—that is, how chemical bonds can form. 

Every atom contains a definite number of electrons. This number, which runs from 1 to more than 100, is characteristic of a neutral atom of a particular element All atoms of hydrogen contain one electron all atoms of the element uranium contain 92 electrons. We will have more to say in Chapter 6 about how these electrons are arranged relative to one another. Right now, you need only know that they are found in the outer regions of the atom, where they form what amounts to a cloud of negative charge. 

Ion formation always involves the movement of electrons from one location to another, yet no matter how ions form, electrons are neither created nor destroyed. In other words, electrons are conserved. The equation for an ionization process makes it appear that an electron has been created Ne Ne + e . Notice from Figure 2-23. however, that a neutral neon atom has 10 electrons, but a neon cation has only 9 electrons. Thus, 10 electrons are present both before and after the formation of the cation. 

Lewis structures are blueprints that show the distribution of valence electrons in molecules. However, the dots and lines of a Lewis structure do not show any details of how bonds form, how molecules react, or the shape of a molecule. In this respect, a Lewis structure is like the electron configuration of an atom both tell us about electron distributions, but neither provides detailed descriptions. Just as we need atomic orbitals to understand how electrons are distributed in an atom, we need an orbital view to understand how electrons are distributed in a molecule. 

Read the entire laboratory activity. Using the above equations to guide you, form a hypothesis about how many copper atoms you expect to lose from the copper anode for each copper atom deposited on the cathode. How many electrons do you expect to pass through the circuit for each copper atom deposited at the cathode Record your hypothesis on page 166. 

In this chapter, a brief review of quantum mechanical methods and the arrangement of electrons in atoms has been presented. These topics form the basis for understanding how quantum mechanics is applied to problems in molecular structure and the chemical behavior of the elements. The properties of atoms discussed in Chapter 1 are directly related to how the electrons are arranged in atoms. Although the presentation in this chapter is not exhaustive, it provides an adequate basis for the study of topics in inorganic chemistry. Further details can be found in the references. 

Equation (10.34) indicates how the intrinsic energy of a chemical bond linking atoms k and I depends on the electronic charges carried by the bond-forming atoms Eki is for a reference bond with net charges qk and (fi at atoms k and I, respectively, whereas Ski corresponds to modified charges qk = qi + Aqk and qi = qf + Aqi. Fki follows from Eq. (10.26). These formulas are the basics of this theory. From here on, we focus on simplifications and application. 

It is easy to see from the examples in the previous section how two identical atoms can share electrons to achieve an octet and form diatomic molecules. Because each of our examples dealt with identical atoms, the electrons can be considered to be shared equally by each atom. The bond formed when the atoms are equally shared can be thought of as a pure covalent bond. But what happens in covalent compounds Remember, a compound contains two different elements. When atoms of two different elements are held together by covalent bonds, there is an unequal sharing of the electrons. The sharing of electrons in a covalent bond may be compared to you and a friend sharing a flashlight while walking down a dark street. If you and your friend both held the... 

The results of some of these techniques are summarized in Table 15 for the situation in pyridin-2-one tautomerism representative results are also included which show how electron withdrawal by insertion of electronegative atoms at position 6 leads to shift of the tautomeric equilibrium towards the hydroxy form. 

Using our shell model to explain how ions form works well for groups 1 and 2 and 13 through 18. This model is too simplified to work well for the transition metals of groups 3 through 12, however, or for the inner transition metals. In general, these metal atoms tend to form positive ions, but the number of electrons lost varies. Depending on conditions, for example, an iron atom may lose two electrons to form the Fe2+ ion, or it may lose three electrons to form the Fe3+ ion. 

Almost all chemical properties can be explained in terms of the properties of atoms, so this material is central to developing an understanding of chemistry. The topics we cover here account for the structure of the periodic table, the great organizing principle of chemistry, and provide a basis for understanding how elements combine to form compounds. The material is also important because it introduces the theory of matter known as quantum mechanics, which is essential for understanding how electrons behave. 

Pauling showed that the quantum mechanical wave functions for s and p atomic orbitals derived from the Schrodinger wave equation (Section 5.7) can be mathematically combined to form a new set of equivalent wave functions called hybrid atomic orbitals. When one s orbital combines with three p orbitals, as occurs in an excited-state carbon atom, four equivalent hybrid orbitals, called sp3 hybrids, result. (The superscript 3 in the name sp3 tells how many p atomic orbitals are combined to construct the hybrid orbitals, not how many electrons occupy each orbital.)... 

A chemical bond forms when atoms gain, lose, or share electrons. How electrons from two or more atoms interact determines the type of chemical bond formed. The interaction of electrons depends on the location and number of electrons in the atom. 

Let s stop a moment and recall where this conversation is going. We want to be able to rationalize the physical and chemical properties we observed for matter. To do this, we need to understand the intermolecular forces that operate between the molecules in a sample, all of which are caused by how electrons are arranged in the molecule. To understand the intermolecular forces, therefore, we need to have some ideas about how molecules are formed, what shape they have, and how the negatively charged electrons are distributed around and among the atoms in the molecule. Now, on to molecular geometry. 

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