Question

when will the central atom in a covalent structure typically have an expanded valence shell (i.e., more than eight outer electrons)?
choose one or more:
surrounding atoms are much smaller than the central atom.
nonzero formal charges on individual atoms can be reduced.
elements from period 3 onward always have expanded valence shells.
surrounding atoms, for example oxygen or a halogen, are highly electronegative.

Explanation:

• When surrounding atoms are much smaller, more can fit around the central atom, allowing for an expanded valence shell.
• Reducing non - zero formal charges often leads to resonance structures or bonding arrangements that result in an expanded valence shell.
• Elements from period 3 and onward can use d - orbitals for bonding and can have expanded valence shells, but not always.
• Highly electronegative surrounding atoms like oxygen or halogens can pull electron density, enabling the central atom to accommodate more electrons in an expanded valence shell.

Answer:

Surrounding atoms are much smaller than the central atom.
Nonzero formal charges on individual atoms can be reduced.
Surrounding atoms, for example oxygen or a halogen, are highly electronegative.