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Questions and Answers
What are the 3 exceptions to the octet rule?
What are the 3 exceptions to the octet rule?
- The species has an odd number of electrons 2. Incomplete octets- when there are too few valence electrons 3. Expanded octets- when the central atoms can have 10, or even 12 electrons (if it is in the 3rd row or lower)
For exception 1, (odd number of electrons), what must there end up being in the Lewis structure?
For exception 1, (odd number of electrons), what must there end up being in the Lewis structure?
A lone electron, which is an unpaired electron
Where is a lone electron usually placed in a Lewis structure?
Where is a lone electron usually placed in a Lewis structure?
It is placed such that the structure will have the lowest/most appropriate set of formal charges
What is formal charge?
What is formal charge?
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Is it common to have molecules with an odd number of electrons?
Is it common to have molecules with an odd number of electrons?
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What is a free radical?
What is a free radical?
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How are free radicals usually shown?
How are free radicals usually shown?
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Give an example of when exception 2 (incomplete octet due to too few valence electrons) occurs?
Give an example of when exception 2 (incomplete octet due to too few valence electrons) occurs?
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Explain when exception 3 occurs.
Explain when exception 3 occurs.
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What is the octet rule based on?
What is the octet rule based on?
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What allows an expanded octet to occur at the 3rd period?
What allows an expanded octet to occur at the 3rd period?
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What is the relationship between the size of the central atom and expanded octets?
What is the relationship between the size of the central atom and expanded octets?
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When do expanded octets generally occur?
When do expanded octets generally occur?
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In cases where an octet is possible, is it plausible that expanded octets are actually more favorable?
In cases where an octet is possible, is it plausible that expanded octets are actually more favorable?
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Study Notes
Exceptions to the Octet Rule
- Exceptions to the octet rule include species with an odd number of electrons, incomplete octets, and expanded octets.
- Odd-electron species result in a lone unpaired electron in Lewis structures.
- Incomplete octets occur when there are too few valence electrons, exemplified by BF3.
- Expanded octets can have central atoms with 10 or even 12 electrons, usually involving electronegative terminal atoms or non-metals in periods 3 or below.
Lone Electrons and Formal Charge
- A lone electron is strategically placed in a Lewis structure to minimize formal charges.
- Formal charge reflects the hypothetical charge of an element if electrons are equally shared in a compound.
- Molecules with odd numbers of electrons, or free radicals, are typically reactive, seeking to pair their unpaired electrons.
Free Radicals
- Free radicals are characterized as reactive species with an odd number of electrons.
- They are generally depicted by placing a dot next to the chemical symbol in structural representations.
Octet Rule Principles
- The octet rule is grounded in the spatial arrangement available in ns and np orbitals.
- For period 3 elements and beyond, an empty d subshell becomes accessible, accommodating expanded octets.
Central Atom Size and Electron Capacity
- A larger central atom allows for a greater number of surrounding electrons, promoting expanded octets.
- Expanded octets are common when central atoms are connected to smaller, highly electronegative atoms, such as F, Cl, and O.
Favorability of Expanded Octets
- In scenarios where octets are feasible, expanded octets might be favored to achieve optimal formal charges, highlighting the importance of considering formal charges during structure evaluation.
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Description
Explore the exceptions to the octet rule in this flashcard quiz. Understand the concepts of odd electron species, incomplete octets, and expanded octets. Perfect for mastering key chemistry principles related to molecular structure.
