BASIC CONCEPTS OF CHEMICAL BONDING

Whenever two atoms or ions are strongly held together, we say there is a chemical bond between them. There are three general types of chemical bonds ionic, covaient, and metaiiic. We can get a glimpse of these three types of bonds by thinking about the simple act of using a stainless-steel 

What determines the type of bonding in any substance How do the characteristics of these bonds give rise to different physical and chemical properties The keys to answering the first question are found in the electronic structure of the atoms involved, discussed in Chapters 6 and 7. In this chapter and the next, we examine the relationship between the electronic structure of atoms and the ionic and covalent chemical bonds they form. We will discuss metalHc bonding in Chapter 12. 

Atomium is a 110-m-high steel sculpture commissioned for the 1958 World s Fair in Brussels. The nine spheres represent atoms, and the connecting rods evoke the chemical bonds holding them together. One sphere sits in the center of a cube formed by the other eight, a common arrangement of the atoms in metallic elements, such as iron. 

We begin with descriptions of the three main types of chemical bonds ionic, covalent, and metallic. In evaluating bonding, Lewis symbols provide a useful shorthand for keeping track of valence electrons. 

2 IONIC BONDING We learn that in ionic substances, the atoms are held together by the electrostatic attractions between ions of opposite charge. We discuss the energetics of forming ionic substances and describe the lattice energy of these substances. 

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One way to answer the aforementioned question is Two atoms form a molecule because the energy of the whole is lower than the sum of the energies of its parts. So the theory we need should bring about a decrease in energy when a molecule is formed by two atoms. As in the case of an atom, the energy of a molecule can also be calculated using quantum mechanical methods. In this chapter, we first use the simplest diatomic molecules Hj and H2 as examples to illustrate the basic concepts of chemical bonding. Then we will turn to other more complicated molecules. 

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