Prelab for VSEPR Theory and Shapes of Molecules Complete the following table: Chemical Species KrF2 PH3 TeCl4 CBr4 HS2 Lewis Structure Perspective Drawing Number of atoms bonded to central atom Number of lone pairs on central atom Electronic geometry Molecular geometry Polarity VSEPR Theory and Shapes of Molecules Page 1 of 1
The Correct Answer and Explanation is:
Of course. Here is the completed table for the VSEPR theory prelab, followed by a detailed explanation.
Completed VSEPR Table
| Chemical Species | KrF₂ | PH₄⁺ | TeCl₄ | ClBr₃ | H₂S |
| Lewis Structure | Kr is the central atom with single bonds to two F atoms. Kr has 3 lone pairs, and each F has 3 lone pairs. | P is the central atom with single bonds to four H atoms. The entire structure is in brackets with a +1 charge. P has no lone pairs. | Te is the central atom with single bonds to four Cl atoms. Te has 1 lone pair, and each Cl has 3 lone pairs. | Cl is the central atom with single bonds to three Br atoms. Cl has 2 lone pairs, and each Br has 3 lone pairs. | S is the central atom with single bonds to two H atoms. S has 2 lone pairs. |
| Perspective Drawing | A linear shape. F atoms are on opposite sides of the central Kr atom (180° apart). Three lone pairs are in a trigonal planar arrangement around Kr’s equator. | A tetrahedral shape. The P atom is in the center. One H is up, one is in the plane, one is on a wedge (forward), and one is on a dash (back). Bond angles are 109.5°. | A seesaw shape. The Te atom is in the center. Two Cl atoms are in axial positions, and two Cl are in equatorial positions. The lone pair is also in an equatorial position. | A T-shaped molecule. The Cl atom is in the center. Two Br atoms are in axial positions, and one Br is in an equatorial position. Two lone pairs are in equatorial positions. | A bent shape. The S atom is at the vertex. Two H atoms are bonded at an angle of <109.5°. Two lone pairs are on the S atom. |
| Number of atoms bonded to central atom | 2 | 4 | 4 | 3 | 2 |
| Number of lone pairs on central atom | 3 | 0 | 1 | 2 | 2 |
| Electronic Geometry | Trigonal Bipyramidal | Tetrahedral | Trigonal Bipyramidal | Trigonal Bipyramidal | Tetrahedral |
| Molecular Geometry | Linear | Tetrahedral | Seesaw | T-shaped | Bent |
| Polarity | Nonpolar | Nonpolar | Polar | Polar | Polar |
Explanation
The VSEPR (Valence Shell Electron Pair Repulsion) theory helps predict the three dimensional shape of molecules. The process involves determining the arrangement of electron pairs around the central atom that minimizes repulsion.
First, we determine the total number of valence electrons for each species. For an ion like phosphonium (PH₄⁺), we subtract an electron for the positive charge. Then, we draw the Lewis structure, placing the least electronegative atom (or the unique atom) in the center and connecting terminal atoms with single bonds. We distribute the remaining electrons as lone pairs, first to the terminal atoms to satisfy their octets, and then any leftover electrons to the central atom.
The number of electron domains, which includes both bonding pairs and lone pairs on the central atom, determines the electronic geometry. For example, H₂S has two bonding pairs and two lone pairs, for a total of four electron domains, giving it a tetrahedral electronic geometry. KrF₂ has five domains (two bonding, three lone), resulting in a trigonal bipyramidal electronic geometry.
The molecular geometry describes the arrangement of only the atoms, not the lone pairs. While H₂S has a tetrahedral electronic geometry, its molecular shape is bent because the two lone pairs on sulfur repel the bonding pairs. Similarly, TeCl₄ has a trigonal bipyramidal electronic geometry, but its one lone pair results in a seesaw molecular shape. For a molecule with no lone pairs on the central atom, like PH₄⁺, the electronic and molecular geometries are the same, which is tetrahedral in this case.
Finally, polarity is determined by both bond polarity and molecular symmetry. A molecule with polar bonds can be nonpolar overall if the shape is symmetrical, allowing the bond dipoles to cancel each other out. KrF₂ is linear and PH₄⁺ is tetrahedral, making them symmetrical and nonpolar. In contrast, TeCl₄ (seesaw), ClBr₃ (T-shaped), and H₂S (bent) are asymmetrical. Their polar bond dipoles do not cancel, resulting in a net molecular dipole, making them polar molecules
