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Ch.10 - Chemical Bonding I: The Lewis Model
All textbooksTro 6th EditionCh.10 - Chemical Bonding I: The Lewis ModelProblem 51
Chapter 10, Problem 51

Use covalent Lewis structures to explain why each element or family of elements occurs as diatomic molecules: a. hydrogen b. the halogens c. oxygen d. nitrogen.

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Hydrogen (H) atoms each have one electron and need one more to achieve a stable electron configuration like helium. By sharing their electrons, two hydrogen atoms form a single covalent bond, resulting in the diatomic molecule H₂.
Halogens (e.g., F, Cl, Br, I) have seven valence electrons and need one more to complete their octet. By sharing one electron with another halogen atom, they form a single covalent bond, resulting in diatomic molecules like F₂, Cl₂, etc.
Oxygen (O) atoms have six valence electrons and need two more to complete their octet. By sharing two pairs of electrons, two oxygen atoms form a double covalent bond, resulting in the diatomic molecule O₂.
Nitrogen (N) atoms have five valence electrons and need three more to complete their octet. By sharing three pairs of electrons, two nitrogen atoms form a triple covalent bond, resulting in the diatomic molecule N₂.
In each case, the formation of diatomic molecules allows the atoms to achieve a more stable electron configuration, similar to that of the nearest noble gas.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Covalent Bonds

Covalent bonds are formed when two atoms share one or more pairs of electrons, allowing them to achieve a more stable electron configuration. This sharing of electrons is crucial for the formation of diatomic molecules, as it enables atoms to fill their outer electron shells, leading to greater stability. For example, in H2, two hydrogen atoms share their single electrons to form a stable bond.
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Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms and the lone pairs of electrons in a molecule. They provide a visual way to understand how atoms bond covalently and the arrangement of electrons. By using Lewis structures, one can predict the formation of diatomic molecules, such as O2 and N2, by illustrating how atoms share electrons to achieve full valence shells.
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Diatomic Molecules

Diatomic molecules consist of two atoms, which can be of the same or different elements. Many elements, particularly nonmetals, naturally exist as diatomic molecules due to their tendency to form stable covalent bonds. For instance, halogens like Cl2 and Br2, as well as nitrogen (N2) and oxygen (O2), are commonly found as diatomic molecules in nature, reflecting their need for stability through electron sharing.
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Related Practice
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Arrange these compounds in order of increasing magnitude of lattice energy: CaO, NaBr, CsI, BaS.

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Use the Born–Haber cycle and data from Appendix IIB, Chapter 9 and this chapter to calculate the lattice energy of LiBr. (ΔHsub for lithium is 138 kJ>mol.)

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Use the Born–Haber cycle and data from Appendix IIB and Table 10.3 to calculate the lattice energy of MgO. (ΔHsub for magnesium is 137 kJ/mol; IE1 and IE2 for magnesium are 738 kJ/mol and 1450 kJ/mol, respectively; EA1 and EA2 for O are −141 kJ/mol and 744 kJ/mol, respectively.)

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