What elements can have an expanded octet

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Deviations from the Octet Rule
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Re: What elements can have expanded octet? [ENDORSED]
Re: What elements can have expanded octet?
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When can elements have expanded octets?
Which elements Cannot have an expanded octet?
Which compound has an expanded octet '?
How do you know which element has expanded octet?

The correct option is (B)

The term expanded octet is defined as when an element is capable of having electrons of more than eight. Elements of the 3rd period and onwards are capable of showing expanded octet while bonding.

Phosphorus (P), Krypton (Kr), and Xenon (Xe) belong to the 3rd, 4th, and 5th periods respectively. They have d and f orbitals for further expansion of their valence shell. Hence, they are capable of expanding their octets.

But in the case of Boron (B), it belongs to group 2. It doesn't contain d orbitals in order to expand its octet.

Learning Objective

Explain why some elements can form an expanded octet

Key Points

Main group elements that form more bonds than would be predicted by the octet rule are called hypervalent compounds, and have what is known as an 'expanded octet,' meaning that there are more than eight electrons around one atom.
The octet rule can be 'expanded' by some elements by utilizing the d-orbitals found in the third principal energy level and beyond. Sulfur, phosphorus, silicon, and chlorine are common examples of elements that form an expanded octet.
Phosphorus pentachloride (PCl5) and sulfur hexafluoride (SF6) are examples of molecules that deviate from the octet rule by having more than 8 electrons around the central atom.

Terms

hypervalent moleculeA molecule that contains an atom from a main group element which deviates from the octet rule by sharing more than eight electrons.
expanded octetA case where an atom shares more than eight electrons with its bonding partners.
main group elementElements that are not part of the transition metal block in the periodic table.

Deviations from the Octet Rule

A hypervalent molecule is a molecule that contains one or more main group elements that bear more than eight electrons in their valence levels as a result of bonding. Phosphorus pentachloride (PCl5), sulfur hexafluoride (SF6), chlorine trifluoride (ClF3), and the triiodide ion (I3−) are examples of hypervalent molecules.

For the elements in the second period of the periodic table (principal energy level n=2), the s2p6 electrons comprise the octet, and no d sublevel exists. As a result, the second period elements (more specifically, the nonmetals C, N, O, F) obey the octet rule without exceptions.

Phosphorus pentachlorideIn the PCl5 molecule, the central phosphorus atom is bonded to five Cl atoms, thus having 10 bonding electrons and violating the octet rule. The overall geometry of the molecule is depicted (trigonal bipyramidal), and bond angles and lengths are highlighted.

However, some of the third-period elements (Si, P, S, and Cl) have been observed to bond to more than four other atoms, and thus need to involve more than the four pairs of electrons available in an s2p6 octet. This is possible because for n=3, the d sublevel exists, and it has five d orbitals. Although the energy of empty 3d-orbitals is ordinarily higher than that of the 4s orbital, that difference is small and the additional d orbitals can accommodate more electrons. Therefore, the d orbitals participate in bonding with other atoms and an expanded octet is produced. Examples of molecules in which a third period central atom contains an expanded octet are the phosphorus pentahalides and sulfur hexafluoride.

Sulfur hexafluorideIn the SF6 molecule, the central sulfur atom is bonded to six fluorine atoms, so sulfur has 12 bonding electrons around it. The overall geometry of the molecule is depicted (tetragonal bipyramidal, or octahedral), and bond angles and lengths are highlighted.

For atoms in the fourth period and beyond, higher d orbitals can be used to accommodate additional shared pairs beyond the octet. The relative energies of the different kinds of atomic orbital reveal that energy gaps become smaller as the principal energy level quantum number (n) increases, and the energetic cost of using these higher orbitals to accommodate bonding electrons becomes smaller.

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AlexandriaHunt2JPosts: 100Joined: Fri Sep 24, 2021 5:38 am

Re: What elements can have expanded octet? [ENDORSED]

Postby AlexandriaHunt2J » Mon Nov 08, 2021 10:22 pm

Elements before period 3 cannot form expanded octets, as n=1 and n=2, meaning only the s and p orbitals exist, which hold a maximum of 8 electrons combined. Elements in period 3 can form expanded octets, as the 3d orbital exists and can hold excess electrons beyond just 8. Common elements in period 3 that form expanded octets include Si, P, S, and Cl.

butteredbreadPosts: 103Joined: Fri Sep 24, 2021 5:25 am

Re: What elements can have expanded octet?

Postby butteredbread » Mon Nov 08, 2021 10:29 pm

some common examples of elements with expanded octets are sulfur, phosphorous, silicon and chlorine. These 4 elements are in the p block of period 3. elements before silicon cannot have an expanded octet because they are only occupying the s and p orbitals.

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When can elements have expanded octets?

An atom like phosphorus or sulfur which has more than an octet is said to have expanded its valence shell. This can only occur when the valence shell has enough orbitals to accommodate the extra electrons.

Which elements Cannot have an expanded octet?

Phosphorous often has 5 orbitals (10 electrons) and sulfur often has 6 orbitals (12 electrons) because they are in the third period, but nitrogen and oxygen can never have expanded octets because they are in the second period and there is not such thing as a 2d orbital.

Which compound has an expanded octet '?

PF5, SF6 and H2SO4 are the examples of expanded octet molecules.

How do you know which element has expanded octet?

If the central atom in a compound has more than 8 electrons after bond formation (shared and unshared/ lone pairs) then the atom has expanded octet, e.g.,.

PCl5 (10 shared electrons, i.e., P has 5 bond pairs with 5 Cl atoms),.

SO3 (three double bonds with 3 oxygen atoms, i.e., 12 shared electrons).