There are 14 total lone pairs in the Xenon Tetrafluoride (XeF4) molecule.
Understanding Lone Pairs in Molecular Structures
Lone pairs are pairs of valence electrons that are not shared with another atom in a covalent bond and are instead exclusively associated with a single atom. These non-bonding electrons significantly influence a molecule's geometry and chemical reactivity, as described by the Valence Shell Electron Pair Repulsion (VSEPR) theory. Understanding how to identify and count lone pairs is crucial for predicting molecular shapes and properties.
What are Lone Pairs?
- Non-bonding Electrons: These electrons reside in the valence shell of an atom but do not participate in forming chemical bonds.
- Influence on Geometry: Lone pairs occupy more space than bonding pairs, leading to distortions in ideal molecular geometries.
- Electron Domain: Both lone pairs and bonding pairs contribute to the electron domain around a central atom.
For a deeper dive into electron domains and molecular geometry, refer to resources like Khan Academy on VSEPR Theory.
Detailed Calculation for XeF4
To determine the total number of lone pairs in XeF4, we need to consider the valence electrons of both the central Xenon (Xe) atom and the surrounding Fluorine (F) atoms.
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Valence Electrons:
- Xenon (Xe) is a noble gas in Group 18, possessing 8 valence electrons.
- Fluorine (F) is a halogen in Group 17, possessing 7 valence electrons.
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Bonding Pairs:
- Xenon is the central atom, forming a single covalent bond with each of the four Fluorine atoms.
- This accounts for 4 bonding pairs around the central Xe atom.
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Lone Pairs on the Central Xe Atom:
- Xenon starts with 8 valence electrons.
- It uses 4 electrons to form the four single bonds with Fluorine atoms (one electron per bond).
- Remaining electrons on Xe = 8 - 4 = 4 electrons.
- These 4 electrons form 2 lone pairs (4 electrons / 2 electrons per lone pair).
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Lone Pairs on the Terminal F Atoms:
- Each Fluorine atom starts with 7 valence electrons.
- Each Fluorine atom uses 1 electron to form a single bond with the Xenon atom.
- Remaining electrons on each F = 7 - 1 = 6 electrons.
- These 6 electrons form 3 lone pairs on each Fluorine atom (6 electrons / 2 electrons per lone pair).
- Since there are four Fluorine atoms, the total lone pairs from terminal atoms = 4 F atoms * 3 lone pairs/F atom = 12 lone pairs.
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Total Lone Pairs in XeF4:
- Total lone pairs = Lone pairs on central Xe + Lone pairs on terminal F atoms
- Total lone pairs = 2 + 12 = 14 lone pairs.
The molecular geometry of XeF4 is square planar due to the two lone pairs on the central Xenon atom influencing the arrangement of the four bonding pairs, resulting in six electron domains around the central atom (four bonding and two non-bonding).
Summary of Electron Distribution
The following table summarizes the electron distribution within the XeF4 molecule:
| Atom Type | Valence Electrons | Electrons in Bonds | Remaining Electrons | Number of Lone Pairs |
|---|---|---|---|---|
| Xenon (Xe) | 8 | 4 (1 per bond to F) | 4 | 2 |
| Fluorine (F) | 7 | 1 (1 per bond to Xe) | 6 | 3 (per F atom) |
| Total F (4 atoms) | - | - | - | 12 (4 * 3) |
| Overall Total | - | - | - | 14 |
