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Ch.8 - Basic Concepts of Chemical Bonding
All textbooksBrown 15th EditionCh.8 - Basic Concepts of Chemical BondingProblem 105c
Chapter 8, Problem 105c

A common form of elemental phosphorus is the tetrahedral P4 molecule, where all four phosphorus atoms are equivalent: 
Draw a Lewis structure for a linear P4 molecule that satisfies the octet rule. Does this molecule have resonance structures?

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1
Step 1: Understand the structure of P4 in its common form. The common form of P4 is a tetrahedral structure where each phosphorus atom is bonded to three others, forming a closed ring.
Step 2: Consider the linear P4 structure. In a linear arrangement, the phosphorus atoms are aligned in a straight line. Each phosphorus atom can form three bonds to satisfy the octet rule.
Step 3: Draw the Lewis structure for linear P4. Start by placing four phosphorus atoms in a line. Connect the first and second, second and third, and third and fourth phosphorus atoms with single bonds.
Step 4: Add lone pairs to each phosphorus atom. Each phosphorus atom should have one lone pair to satisfy the octet rule, as each atom will have three bonds and one lone pair.
Step 5: Consider resonance structures. Evaluate if there are any possible resonance structures by checking if the electrons can be rearranged without changing the connectivity of the atoms. In this case, the linear P4 does not have resonance structures as the electron arrangement is fixed to satisfy the octet rule.

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Key Concepts

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

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help visualize the arrangement of electrons and the connectivity of atoms, which is crucial for understanding molecular geometry and reactivity. In the case of P4, drawing the Lewis structure involves placing electrons around the phosphorus atoms to satisfy the octet rule.
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Octet Rule

The octet rule is a chemical rule of thumb that states atoms tend to bond in such a way that they each have eight electrons in their valence shell, achieving a stable electron configuration similar to that of noble gases. For phosphorus, which can expand its octet due to its position in the periodic table, this rule guides the arrangement of electrons in the Lewis structure, particularly when considering alternative bonding scenarios.
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Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. They are used when a single Lewis structure cannot adequately represent a molecule's electron distribution. In the case of a linear P4 molecule, exploring resonance structures can reveal how electrons are shared among the phosphorus atoms, potentially leading to multiple valid representations of the molecule.
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Related Practice
Textbook Question

Under special conditions, sulfur reacts with anhydrous liquid ammonia to form a binary compound of sulfur and nitrogen. The compound is found to consist of 69.6% S and 30.4% N. Measurements of its molecular mass yield a value of 184.3 g/mol. The compound occasionally detonates on being struck or when heated rapidly. The sulfur and nitrogen atoms of the molecule are joined in a ring. All the bonds in the ring are of the same length. (a) Calculate the empirical and molecular formulas for the substance.

Textbook Question

A common form of elemental phosphorus is the tetrahedral P4 molecule, where all four phosphorus atoms are equivalent: 

(b) How many P-P bonds are there in the molecule?