Draw Lewis structure for XeF4 and answer the following questions based on your drawing: 1. For the central xenon atom: The number of lone pairs The number of single bonds The number of double bonds 2. The central xenon atom: A. Obeys the octet rule B. Has an incomplete octet C. Has an expanded octet.
The Correct Answer and Explanation is:
Lewis Structure of XeF₄ (Xenon Tetrafluoride):
To draw the Lewis structure of XeF₄:
- Count the total valence electrons:
- Xenon (Xe) has 8 valence electrons.
- Each fluorine (F) has 7 valence electrons. With 4 fluorines, that gives 4 × 7 = 28.
- Total valence electrons = 8 (Xe) + 28 (F) = 36 electrons.
- Place Xe in the center since it is the least electronegative, and attach the four fluorine atoms to it using single bonds.
- Each single bond uses 2 electrons: 4 bonds × 2 = 8 electrons.
- Subtract used electrons: 36 − 8 = 28 electrons remaining.
- Distribute remaining electrons to satisfy octets of the fluorines.
- Each F needs 6 more electrons to complete its octet (3 lone pairs).
- 4 fluorines × 6 electrons = 24 electrons.
- Remaining electrons after fluorine octets: 28 − 24 = 4 electrons.
- Place the remaining 4 electrons (2 lone pairs) on the central xenon atom.
Answers:
1. For the central xenon atom:
- Number of lone pairs: 2
- Number of single bonds: 4
- Number of double bonds: 0
2. The central xenon atom:
- C. Has an expanded octet
Explanation
Xenon tetrafluoride (XeF₄) is a molecule composed of one xenon atom bonded to four fluorine atoms. Xenon is a noble gas, and it might seem unusual for it to form compounds. However, due to the availability of empty d-orbitals, xenon can expand its valence shell and accommodate more than eight electrons. This is evident in XeF₄, where the central xenon atom is surrounded by twelve electrons: eight from the four single bonds with fluorine atoms and four from two lone pairs.
In the Lewis structure, each fluorine atom forms a single bond with xenon and holds three lone pairs to satisfy the octet rule. The central xenon atom, after forming four bonds (8 electrons), still has 4 more electrons (2 lone pairs) placed on it. This gives a total of 12 electrons around xenon, meaning xenon exceeds the octet rule.
The presence of an expanded octet is typical for elements in period 3 and beyond of the periodic table. These elements have access to d-orbitals, which allow them to accommodate more than eight electrons. In the case of xenon, this is chemically feasible and energetically favorable in compounds like XeF₄.
There are no double bonds in this structure. The fluorine atoms are highly electronegative and typically form only single bonds. The geometry of XeF₄ is square planar due to the presence of two lone pairs on xenon, which repel each other and the bonding pairs, arranging the atoms in a flat square around the central atom to minimize repulsion.
Thus, the central xenon atom in XeF₄ has 2 lone pairs, 4 single bonds, no double bonds, and an expanded octet.
