General Chemistry Principles, Patterns, and Applications, 2011

2. Is a Lewis dot symbol an exact representation of the valence electrons in an atom or ion? Explain your
answer.
3. How can the Lewis electron dot system help to predict the stoichiometry of a compound and its chemical and
physical properties?
4. How is a Lewis dot symbol consistent with the quantum mechanical model of the atom described in Chapter
6 "The Structure of Atoms"? How is it different?
A N S W E R
3. Lewis dot symbols allow us to predict the number of bonds atoms will form, and therefore the
stoichiometry of a compound. The Lewis structure of a compound also indicates the presence or absence of
lone pairs of electrons, which provides information on the compound’s chemical reactivity and physical
properties.
8.5 Lewis Structures and Covalent Bonding
L E A R N I N G O B JE C T I V E S
1. To use Lewis dot symbols to explain the stoichiometry of a compound.
2. To understand the concept of resonance.
We begin our discussion of the relationship between structure and bonding in covalent compounds by describing the
interaction between two identical neutral atoms—for example, the H2 molecule, which contains a purely covalent
bond. Each hydrogen atom in H2 contains one electron and one proton, with the electron attracted to the proton by
electrostatic forces. As the two hydrogen atoms are brought together, additional interactions must be considered
(Figure 8.8 "Attractive and Repulsive Interactions between Electrons and Nuclei in the Hydrogen Molecule"):
The electrons in the two atoms repel each other because they have the same charge
(E > 0).
Similarly, the protons in adjacent atoms repel each other (E > 0).
The electron in one atom is attracted to the oppositely charged proton in the other atom
and vice versa (E < 0). [1]
Figure 8.8 Attractive and Repulsive Interactions between Electrons and Nuclei in the Hydrogen Molecule
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