Common Molecules with Expanded Octets: Examples and Lewis Structures

📚 Quick Study Guide

• ⚛️ Expanded octet molecules have a central atom with more than eight valence electrons.
• 🔑 This is possible for elements in the 3rd period or beyond because they have available *d* orbitals.
• 🧪 Common examples include $SF_6$, $PCl_5$, and $XeF_4$.
• 📝 To draw Lewis structures for expanded octet molecules:
  1. Calculate the total number of valence electrons.
  2. Place the least electronegative element in the center (usually).
  3. Form single bonds between the central atom and surrounding atoms.
  4. Distribute remaining electrons to fulfill the octet rule for surrounding atoms first.
  5. If there are leftover electrons, place them around the central atom.
• 📐 The shape of molecules with expanded octets is determined by VSEPR theory.

🧪 Practice Quiz

1. Which of the following molecules has an expanded octet?
   1. $CO_2$
   2. $H_2O$
   3. $SF_6$
   4. $NH_3$
2. Which element is most likely to be the central atom in a molecule with an expanded octet?
   1. Oxygen
   2. Carbon
   3. Sulfur
   4. Nitrogen
3. How many valence electrons are present in $PCl_5$?
   1. 36
   2. 40
   3. 32
   4. 28
4. What is the shape of the $XeF_4$ molecule?
   1. Tetrahedral
   2. Square planar
   3. Trigonal bipyramidal
   4. Octahedral
5. Which of the following is NOT a valid reason for an atom to exhibit an expanded octet?
   1. Availability of d-orbitals
   2. Low electronegativity
   3. Being in the second period
   4. Having more than 8 valence electrons
6. In $IF_5$, how many lone pairs are on the central iodine atom?
   1. 0
   2. 1
   3. 2
   4. 3
7. Which molecule has a central atom with 12 electrons around it?
   1. $SF_4$
   2. $PCl_3$
   3. $XeF_2$
   4. $SF_6$