National Geographic

Figure 3.12 Atoms gain stability by sharing, gaining, or losing electrons to form ions and molecules. The properties of metals can be explained by metallic bonds.

Covalent bond Shared electrons fill outermost energy levels and make stable molecular compounds.

Metallic bond Within metals, valence electrons move freely around positively charged protons.

Ionic bond Once valence electrons are gained or lost to fill outermost energy levels and form stable ions, the oppositely charged ions are attracted to each other.

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Copper Nitrate BondingSilver Nitrate And Copper Wire
Figure 3.13 When a copper wire is placed in the solution of silver nitrate in the beaker, a chemical reaction occurs in which silver replaces copper in the wire and an aqua-colored copper nitrate solution forms.

Chemical Reactions

You have learned that atoms gain, lose, or share electrons to become more stable and that these atoms form compounds. Sometimes, compounds break down into simpler substances. The change of one or more substances into other substances, such as those in Figure 3.13, is called a chemical reaction. Chemical reactions are described by chemical equations. For example, water (H2O) is formed by the chemical reaction between hydrogen gas (H2) and oxygen gas (O2). The formation of water can be described by the following chemical equation.

You can read this chemical equation as "two molecules of hydrogen and one molecule of oxygen react to yield two molecules of water." In this reaction, hydrogen and oxygen are the reactants and water is the product. When you write a chemical equation, you must balance the equation by showing an equal number of atoms for each element on each side of the equation. Therefore, the same amount of matter is present both before and after the reaction. Note that there are four hydrogen atoms on each side of the above equation (2 x 2 = 4). There are also two oxygen atoms on each side of the equation.

Another example of a chemical reaction, one that takes place between iron (Fe) and oxygen (O), is represented by the following chemical equation.

You will examine how compounds form in the Problem-Solving Lab on this page.

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Solar Panel Basics

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