IB Chemistry Topic S2.2.13 Expanded Octet of Electrons Revision Notes (HL)

IB Chemistry Topic S2.2.13 Expanded Octet of Electrons Revision Notes (HL) | RevisionDojo

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Some Atoms Can Form Molecules with Expanded Octets

Expanded Octets and Their Connection to the Periodic Table

Definition

Octet rule

Atoms are driven by their quest for stability, often achieved by attaining a noble gas electron configuration, commonly referred to as the octet rule.

However, some elements in Period 3 and beyond (such as phosphorus, sulfur, and xenon) can exceed this limit.
These atoms can hold more than eight electrons in their valence shell because they are larger than Period 2 atoms, leaving enough room around the central atom to fit more than four bonded pairs.

Why Only Period 3 and Beyond?

Larger Atomic Radius
1. Atoms in Period 3 and beyond are bigger, so their valence electrons sit further from the nucleus and there is more space around the central atom.
2. This extra space lets the central atom surround itself with more than four bonded pairs without too much repulsion, so it can exceed eight valence electrons.
Why Not d Orbitals?
1. Older explanations claimed that empty 3d orbitals accept the extra electrons, but these orbitals are too high in energy to play a real part in bonding.
2. The expansion is better explained by atom size, so the modern model does not rely on d orbitals.

Note

Elements in Periods 1 and 2 cannot expand their octet because they are too small to fit more than four electron pairs around the central atom.

Visualizing Lewis Structures for Expanded Octets

To understand expanded octets, let’s explore how to draw Lewis structures for molecules where the central atom has more than four bonds (or electron domains).

Steps to Draw Lewis Structures for Expanded Octets:

Count Valence Electrons:

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Some Atoms Can Form Molecules with Expanded Octets

Expanded Octets and Their Connection to the Periodic Table

Definition

Octet rule

Atoms are driven by their quest for stability, often achieved by attaining a noble gas electron configuration, commonly referred to as the octet rule.

However, some elements in Period 3 and beyond (such as phosphorus, sulfur, and xenon) can exceed this limit.
These atoms can hold more than eight electrons in their valence shell because they are larger than Period 2 atoms, leaving enough room around the central atom to fit more than four bonded pairs.

Why Only Period 3 and Beyond?

Larger Atomic Radius
1. Atoms in Period 3 and beyond are bigger, so their valence electrons sit further from the nucleus and there is more space around the central atom.
2. This extra space lets the central atom surround itself with more than four bonded pairs without too much repulsion, so it can exceed eight valence electrons.
Why Not d Orbitals?
1. Older explanations claimed that empty 3d orbitals accept the extra electrons, but these orbitals are too high in energy to play a real part in bonding.
2. The expansion is better explained by atom size, so the modern model does not rely on d orbitals.

Note

Elements in Periods 1 and 2 cannot expand their octet because they are too small to fit more than four electron pairs around the central atom.

Visualizing Lewis Structures for Expanded Octets

To understand expanded octets, let’s explore how to draw Lewis structures for molecules where the central atom has more than four bonds (or electron domains).

Steps to Draw Lewis Structures for Expanded Octets:

Count Valence Electrons:

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Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

IB Chemistry S2.2.13 Expanded Octet of Electrons Notes

Structure 1. Models of the particulate nature of matter5 subtopics

Structure 2. Models of bonding and structure4 subtopics

Structure 3. Classification of matter2 subtopics

Reactivity 1. What drives chemical reactions?4 subtopics

Reactivity 2. How much, how fast and how far?3 subtopics

Reactivity 3. What are the mechanisms of chemical change?4 subtopics

Some Atoms Can Form Molecules with Expanded Octets

Expanded Octets and Their Connection to the Periodic Table

Why Only Period 3 and Beyond?

Visualizing Lewis Structures for Expanded Octets

Steps to Draw Lewis Structures for Expanded Octets:

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Duis aute irure dolor in reprehenderit

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Some Atoms Can Form Molecules with Expanded Octets

Expanded Octets and Their Connection to the Periodic Table

Why Only Period 3 and Beyond?

Visualizing Lewis Structures for Expanded Octets

Steps to Draw Lewis Structures for Expanded Octets:

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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