When the atoms linked by a covalent bond are different, the bonding electrons are shared, but no longer equally. Since the bonding atoms are identical, Cl 2 also features a pure covalent bond. The total number of electrons around each individual atom consists of six nonbonding electrons and two shared (i.e., bonding) electrons for eight total electrons, matching the number of valence electrons in the noble gas argon. The bond length is determined by the distance at which the lowest potential energy is achieved. If the atoms continue to approach each other, the positive charges in the two nuclei begin to repel each other, and the potential energy increases. The strong attraction of each shared electron to both nuclei stabilizes the system, and the potential energy decreases as the bond distance decreases. The single electrons on each hydrogen atom then interact with both atomic nuclei, occupying the space around both atoms. As the two atoms approach each other (moving left along the x-axis), their valence orbitals (1 s) begin to overlap. Along the x-axis is the distance between the two atoms. Starting on the far right, we have two separate hydrogen atoms with a particular potential energy, indicated by the red line. Figure 7.4 illustrates why this bond is formed. For example, the hydrogen molecule, H 2, contains a covalent bond between its two hydrogen atoms. Nonmetal atoms frequently form covalent bonds with other nonmetal atoms. Furthermore, whereas ionic compounds are good conductors of electricity when dissolved in water, most covalent compounds are insoluble in water since they are electrically neutral, they are poor conductors of electricity in any state. In fact, many covalent compounds are liquids or gases at room temperature, and, in their solid states, they are typically much softer than ionic solids. Because the attraction between molecules, which are electrically neutral, is weaker than that between electrically charged ions, covalent compounds generally have much lower melting and boiling points than ionic compounds. For example, two hydrogen atoms bond covalently to form an H 2 molecule each hydrogen atom in the H 2 molecule has two electrons stabilizing it, giving each atom the same number of valence electrons as the noble gas He.Ĭompounds that contain covalent bonds exhibit different physical properties than ionic compounds. Covalent bonds are formed between two atoms when both have similar tendencies to attract electrons to themselves (i.e., when both atoms have identical or fairly similar ionization energies and electron affinities). A different type of bonding results from the mutual attraction of atoms for a “shared” pair of electrons. Ionic bonding results from the electrostatic attraction of oppositely charged ions that are typically produced by the transfer of electrons between metallic and nonmetallic atoms. Define electronegativity and assess the polarity of covalent bonds.Describe the formation of covalent bonds. By the end of this section, you will be able to:
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