Neither carbon tetrachloride nor trans CHBr=CHBr have dipole moments. Both have cery different molecular geometries. What are their molecular geometries, and why are they different?
To determine the molecular geometries of carbon tetrachloride (CCl4) and trans CHBr=CHBr, you first need to examine their Lewis structures.
For carbon tetrachloride (CCl4), start with the Lewis structure of carbon (C) and four chlorine (Cl) atoms. Carbon is the central atom with four single bonds to the chlorine atoms, and the chlorine atoms are symmetrically arranged around the carbon atom in a tetrahedral shape.
To determine the geometry of CCl4, we use the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that the electron pairs around a central atom will position themselves as far apart as possible to minimize repulsion. In CCl4, there are four bonding pairs (from the carbon-chlorine bonds) and no lone pairs of electrons. According to VSEPR theory, this arrangement results in a tetrahedral geometry.
For trans CHBr=CHBr, begin with the Lewis structure of each molecule. Simply put, the molecule consists of two carbon (C) atoms double-bonded to each other, with each carbon atom bonded to two bromine (Br) atoms. The double bond restricts the molecular geometry and overall shape of the molecule.
The VSEPR theory helps determine the geometry by considering the bonding and lone pairs around the central atoms. In the case of trans CHBr=CHBr, each carbon atom has one lone pair and two bonding pairs (from the carbon-bromine bonds), resulting in a trigonal planar geometry.
The reason carbon tetrachloride has a tetrahedral geometry while trans CHBr=CHBr has a trigonal planar geometry is due to the different electronic arrangements around their respective central atoms. Carbon in carbon tetrachloride forms four sigma bonds to the chlorine atoms, resulting in a tetrahedral geometry. On the other hand, in trans CHBr=CHBr, the carbon atoms form a double bond with each other, which restricts the geometry to a trigonal planar shape.