Use the VSEPR theory to predict the shape of each molecule. A. SeO2 B. SeBr2 C. CCl4
The correct answer and explanation is:
Correct Answers using VSEPR Theory:
A. SeO₂ – Bent
B. SeBr₂ – Bent
C. CCl₄ – Tetrahedral
Explanation (VSEPR Theory):
The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the shape of molecules based on the idea that electron pairs around a central atom repel each other and thus will arrange themselves to be as far apart as possible. The molecular shape depends on the number of bonding pairs and lone pairs of electrons around the central atom.
A. Selenium dioxide (SeO₂):
Selenium (Se) is the central atom. It forms two double bonds with oxygen atoms and also has one lone pair of electrons. According to VSEPR, this gives a steric number of 3 (two bonding domains + one lone pair). This results in a trigonal planar electron geometry, but the presence of a lone pair causes the molecular shape to be bent. The bond angle is slightly less than 120° because the lone pair exerts greater repulsion than bonding pairs.
B. Selenium dibromide (SeBr₂):
Selenium again is the central atom, bonded to two bromine atoms and holding two lone pairs of electrons. This gives a steric number of 4 (two bonding pairs + two lone pairs). The electron geometry is tetrahedral, but due to the two lone pairs, the actual molecular shape becomes bent. The bond angle is reduced to about 104.5°, similar to that of water.
C. Carbon tetrachloride (CCl₄):
Carbon is the central atom and forms four single covalent bonds with chlorine atoms. There are no lone pairs on the central atom, giving a steric number of 4. The electron geometry and molecular shape are both tetrahedral, with bond angles of approximately 109.5°. The symmetry of CCl₄ makes it a nonpolar molecule despite having polar bonds.
In summary, VSEPR theory helps determine that SeO₂ and SeBr₂ are bent due to lone pairs, while CCl₄ is tetrahedral due to four bonding pairs with no lone pairs.