1. [ PF4 ]+
(a) What is the electron-group geometry, according to VSEPR theory?
(b) What is the molecular geometry?
(c) Is this species polar or nonpolar?
(a) The electron-group geometry is tetrahedral.
(b) The molecular geometry is also tetrahedral.
(c) This species is nonpolar because the four fluorine atoms are arranged symmetrically around the central phosphorus atom.
To determine the electron-group geometry, molecular geometry, and polarity of PF4- according to the VSEPR theory, we need to follow a few steps.
1. Determine the Lewis structure of PF4-:
To do this, start by counting the total number of valence electrons. Phosphorus (P) is in Group 5A and has 5 valence electrons, while each fluorine (F) atom contributes 7 valence electrons. Also, since we have a negative charge (-1), we need to add one extra electron. Therefore, the total number of valence electrons for PF4- is:
5 (P) + 4 (F) + 1 (extra electron) = 10 valence electrons
Distribute the electrons around the atoms, giving the following structure:
F-P-F (each F has six dots, representing bonding pairs, and two dots, representing lone pairs)
|
F
2. Determine the electron-group geometry:
Since there are five electron pairs around the central atom (phosphorus), which includes four bonding pairs (from the four fluorine atoms) and one lone pair (the extra electron), the electron-group geometry is "trigonal bipyramidal."
3. Determine the molecular geometry:
To determine the molecular geometry, consider only the positions of the atoms (not the lone pairs). In the case of PF4-, all the positions will be occupied by fluorine atoms. Since all the positions are filled, the molecular geometry is "tetrahedral."
4. Determine the polarity:
To determine the polarity, we need to consider the molecular geometry and the electronegativity of the atoms involved.
In PF4-, the four fluorine atoms surrounding the central phosphorus atom exert an equal and opposite pull on the shared electron pairs. Therefore, the molecule is symmetrical, resulting in no net dipole moment. Hence, PF4- is a nonpolar species.
To summarize:
(a) The electron-group geometry of PF4- is trigonal bipyramidal.
(b) The molecular geometry of PF4- is tetrahedral.
(c) PF4- is a nonpolar species.
(a) To determine the electron-group geometry, we first need to count the number of electron groups around the central atom. In this case, the central atom is phosphorus (P) and it is bonded to four fluorine (F) atoms. Additionally, there are no lone pairs present on the central atom.
Hence, the electron-group geometry for PF4 is tetrahedral, as it has four electron groups (four bonding pairs) around the central atom.
(b) To determine the molecular geometry, we need to consider the arrangement of atoms around the central atom. As there are no lone pairs on the central atom, the molecular geometry will be the same as the electron-group geometry. Hence, the molecular geometry for PF4 is also tetrahedral.
(c) Since all bonds in PF4 are between the same atom (F), and the molecule has a symmetrical arrangement, it is a nonpolar molecule.