Textbook Question
(b) Which of these compounds or ions is an exception to the octet rule: borohydride (BH4-), borazine (B3N3H6, which is analogous to benzene with alternating B and N in the ring), or boron trichloride?
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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 63
Draw the Lewis structures for each of the following ions or molecules. Identify those in which the octet rule is not obeyed; state which atom in each compound does not follow the octet rule; and state, for those atoms, how many electrons surround them: (a) HCl, (b) ICl5, (c) NO, (d) CF2Cl2, (e) I3-.
Verified step by step guidance1
Step 1: Begin by determining the total number of valence electrons for each molecule or ion. For neutral molecules, sum the valence electrons of all atoms. For ions, adjust the total by adding electrons for negative charges or subtracting for positive charges.
Step 2: Draw the skeletal structure of each molecule or ion, connecting atoms with single bonds. Typically, the least electronegative atom is placed in the center, except for hydrogen, which is always terminal.
Step 3: Distribute the remaining valence electrons as lone pairs, starting with the outer atoms, to satisfy the octet rule (or duet for hydrogen). If electrons remain, place them on the central atom.
Step 4: Check each structure to see if the octet rule is satisfied for each atom. Identify any exceptions to the octet rule, such as molecules with an odd number of electrons, atoms with less than an octet, or atoms with more than an octet (expanded octet).
Step 5: For each exception identified, specify which atom does not follow the octet rule and count the number of electrons surrounding it.
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 use dots to represent valence electrons and lines to represent bonds between atoms. Understanding how to draw these structures is essential for visualizing molecular geometry and predicting reactivity.
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04:28
Lewis Dot Structures: Ions
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. However, there are exceptions to this rule, particularly for elements in periods greater than two and for certain ions and molecules.
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01:27Octet Rule
Exceptions to the Octet Rule
Certain atoms can have fewer or more than eight electrons in their valence shell, leading to exceptions to the octet rule. For example, elements like hydrogen and helium are stable with two electrons, while elements like phosphorus and sulfur can expand their octet to accommodate more than eight electrons. Identifying these exceptions is crucial for accurately interpreting Lewis structures.
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01:27Octet Rule
Related Practice
Textbook Question
For Group 13–17 elements in the third row of the periodic tableand beyond, the octet rule is often not obeyed. A friendof yours says this is because these heavier elements are morelikely to make double or triple bonds. Another friend ofyours says that this is because the heavier elements are largerand can make bonds to more than four atoms at a time.Which friend is more correct?
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Textbook Question
Draw the Lewis structures for each of the following molecules or ions. Identify instances where the octet rule is not obeyed; state which atom in each compound does not follow the octet rule; and state how many electrons surround these atoms: (a) PF6-, (b) BeCl2, (c) NH3, (d) XeF2O (the Xe is the central atom), (e) SO42- .
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Textbook Question
In the vapor phase, BeCl2 exists as a discrete molecule. (a) Draw the Lewis structure of this molecule, using only single bonds. Does this Lewis structure satisfy the octet rule?
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Textbook Question
In the vapor phase, BeCl2 exists as a discrete molecule. (b) What other resonance structures are possible that satisfy the octet rule?