Draw the Lewis structure of KrF4, then answer the following questions. The electron group geometry of KrF4 is – A. trigonal bipyramid B. seesaw or sawhorse C. T-shape D. octahedral E.square pyramid F. square planar. The molecular shape of KrF4 is — A. trigonal bipyramid B. seesaw or sawhorse C. T-shape D. octahedral E. square pyramid F. square planar. The Kr-F bond is — A. polar B. nonpolar. The F-Kr-F bond angle is approximately — A. 90? B. 120? C. 109? D. 90? and 120? E. 180?. A KrF4 molecule is — A. nonpolar B. polar.
The Correct Answer and Explanation is:1
Answers
| Property | Correct choice |
|---|---|
| Electron-group geometry of KrF₄ | D. octahedral |
| Molecular shape (actual geometry) | F. square planar |
| Individual Kr–F bond | A. polar |
| F–Kr–F bond angle (between adjacent F atoms) | A. ≈ 90 ° |
| Overall polarity of the KrF₄ molecule | A. nonpolar |
Why those answers are correct
- Lewis structure and electron counting
Krypton brings 8 valence electrons and each of the four fluorine atoms 7, for a total of
8+4×7=368 + 4\times7 = 36 e⁻.- Place Kr in the center, bond it to four F atoms (8 e⁻).
- Give each F three lone pairs (24 e⁻).
- The remaining 4 e⁻ stay on Kr as two lone pairs.
Six regions of electron density (4 σ-bonds + 2 lone pairs) surround Kr.
- Electron-group geometry: octahedral
VSEPR treats every region—bonding or lone pair—the same when defining the electron-group (or steric) geometry. Six regions arrange themselves at the corners of an octahedron to minimize repulsion, so the correct electron-group geometry is octahedral. - Molecular shape: square planar
Two of the six positions in an octahedron can be occupied by the lone pairs. They adopt opposite (axial) sites to keep as far apart as possible, leaving four fluorines in the equatorial plane. The visible shape formed by the atoms is therefore square planar. - Bond polarity vs. molecular polarity
A Kr–F bond is polar because fluorine (χ ≈ 3.98) is appreciably more electronegative than krypton (χ ≈ 3.0). However, in a perfect square planar arrangement the four bond dipoles point toward the corners of a square and cancel vectorially. Consequently, the whole molecule is non-polar despite having four polar bonds. - Bond angles
In a square plane, the angle between adjacent fluorines is 90 °, while diametrically opposite fluorines are 180 ° apart. Textbook multiple-choice questions usually focus on the characteristic 90 ° value, so ≈ 90 ° is the best single answer among the options provided.
Thus, octahedral electron grouping, square-planar molecular shape, polar bonds, 90 ° F–Kr–F angles, and net non-polarity together describe KrF₄ accurately
