Using only the periodic table as your guide, select the most electronegative atom in each of the following sets: (a) Se, Te, Br, I; (b) Be, Mg, C, Si (c) Al, Si, P, S (d) Zn, Ge, Ga, As.
Ch.8 - Basic Concepts of Chemical Bonding
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
Chapter 8, Problem 36c
(c) Do you expect the O—O bond in H2O2 to be longer or shorter than the O—O bond in O2? Explain.
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Identify the molecular structure of both H2O2 (hydrogen peroxide) and O2 (oxygen gas). Hydrogen peroxide has a bent structure due to the presence of lone pairs on oxygen atoms, while oxygen gas is a diatomic molecule with a double bond between the oxygen atoms.
Consider the types of bonds present in each molecule. In H2O2, the oxygen atoms are connected by a single bond, whereas in O2, the oxygen atoms are connected by a double bond.
Recall that double bonds are generally shorter and stronger than single bonds due to the increased electron density between the atoms.
Apply the concept that the length of the bond is inversely related to the bond order (number of chemical bonds between a pair of atoms). A higher bond order typically results in a shorter bond.
Conclude that based on the bond order and the type of bonding, the O—O bond in O2 (double bond) is expected to be shorter than the O—O bond in H2O2 (single bond).

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bond Length
Bond length refers to the distance between the nuclei of two bonded atoms. It is influenced by factors such as atomic size, bond order, and the presence of lone pairs. Generally, shorter bonds indicate stronger interactions between atoms, while longer bonds suggest weaker interactions.
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Average Bond Order
Bond Order
Bond order is a measure of the number of chemical bonds between a pair of atoms. In simple terms, a higher bond order (e.g., double or triple bonds) typically results in shorter bond lengths due to increased electron sharing. In contrast, a single bond has a lower bond order and is usually longer.
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Lone Pairs and Steric Effects
Lone pairs are pairs of valence electrons that are not involved in bonding. In molecules like H2O2, the presence of lone pairs on oxygen atoms can create repulsive forces that affect bond lengths. This steric effect can lead to longer bond lengths compared to molecules with fewer or no lone pairs, such as O2.
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Related Practice
Textbook Question
Textbook Question
(b) How many bonding electrons are in the structure?
Textbook Question
(c) Would you expect the O—O bond in O2 to be shorter or longer than the O—O bond in compounds that contain an O—O single bond? Explain.
Textbook Question
(a) Construct a Lewis structure for hydrogen peroxide, H2O2, in which each atom achieves an octet of electrons.
Textbook Question
Which of the following statements about electronegativity is false? (a) Electronegativity is the ability of an atom in a molecule to attract electron density toward itself. (b) Electronegativity is the same thing as electron affinity. (c) The numerical values for electronegativity have no units. (d) Fluorine is the most electronegative element. (e) Cesium is the least electronegative element.
