What is the molecular geometry of the ClF4− ion?
Select one:
a. trigonal pyramidal
b. seesaw
c. square planar
d. square pyramidal
e. tetrahedral
The Correct Answer and Explanation is :
The correct answer is d. square pyramidal.
Explanation:
The ClF₄⁻ ion (chlorine tetrafluoride anion) has a central chlorine atom surrounded by four fluorine atoms, and one extra electron due to the negative charge, which influences the overall shape of the molecule.
- Electron Pair Geometry:
- Chlorine (Cl) is in Group 17 of the periodic table, so it typically has 7 valence electrons. The negative charge on the ion adds one more electron, giving chlorine a total of 8 valence electrons. Each of the four fluorine atoms contributes one electron, forming four bonding pairs.
- To accommodate these 5 electron pairs (4 bonding pairs and 1 lone pair), we use the VSEPR (Valence Shell Electron Pair Repulsion) theory. According to VSEPR theory, 5 electron pairs around a central atom arrange themselves in a trigonal bipyramidal geometry to minimize repulsion.
- Lone Pair Influence:
- In the case of ClF₄⁻, the lone pair will occupy one of the equatorial positions in the trigonal bipyramidal arrangement. The lone pair causes distortion because lone pairs exert more repulsion than bonding pairs.
- Molecular Geometry:
- After accounting for the lone pair, the arrangement of the four fluorine atoms forms a square pyramidal shape. Four fluorine atoms occupy the equatorial positions, forming a square plane, while the fifth fluorine atom occupies the axial position, forming the pyramid’s apex.
Thus, the molecular geometry of ClF₄⁻ is square pyramidal, which is consistent with the arrangement of the five electron pairs and the effects of the lone pair on the shape.