Select all cases where the substance shown has a molecular dipole.
CHF3 fluoroform
H2NCH2CH2OH ethanolamine
CF3CF3 hexafluoroethane
CCl2CCl2 tetrachloroethylene
(CH3)3N trimethylamine
CHFCHF cis-1,2-difluoroethene
None
To determine if a substance has a molecular dipole, we need to consider the electronegativity difference between the atoms and the molecular geometry.
A molecular dipole occurs when there is an unequal distribution of electron density in a molecule due to the difference in electronegativity between atoms. This creates a partial positive charge (δ+) and a partial negative charge (δ-) within the molecule.
In general, if a molecule has polar bonds, it may have a molecular dipole. A polar bond is formed between atoms with different electronegativities, meaning one atom attracts the shared electrons more strongly than the other, creating partial positive and negative charges.
Let's analyze each of the given substances:
1. CHF3 (fluoroform): Carbon and fluorine have a significant electronegativity difference, so the C-F bonds are polar. Since the molecule is trigonal pyramidal (a tetrahedral arrangement with one missing vertex), the individual bond dipoles do not cancel out. Therefore, CHF3 has a molecular dipole.
2. H2NCH2CH2OH (ethanolamine): This molecule has multiple groups attached to a central nitrogen atom. The electronegativity difference between nitrogen and hydrogen creates polar N-H bonds. However, the presence of the hydroxyl group (-OH) also contributes to the polarity of the molecule. Considering the overall structure and the presence of multiple polar bonds, ethanolamine has a molecular dipole.
3. CF3CF3 (hexafluoroethane): This molecule consists of carbon and fluorine atoms. While the C-F bonds are polar due to the electronegativity difference, the molecular structure of hexafluoroethane is symmetrical, canceling out the individual bond dipoles. Therefore, CF3CF3 does not have a molecular dipole.
4. CCl2CCl2 (tetrachloroethylene): This molecule contains carbon and chlorine atoms. The C-Cl bonds are polar because of the electronegativity difference. Similar to hexafluoroethane, the structure is symmetrical, and the individual bond dipoles cancel out. Thus, CCl2CCl2 does not have a molecular dipole.
5. (CH3)3N (trimethylamine): Nitrogen is less electronegative than carbon and hydrogen, resulting in polar N-C and N-H bonds in this molecule. However, the molecular structure is pyramidal, meaning the individual bond dipoles do not cancel out. Hence, (CH3)3N has a molecular dipole.
6. CHFCHF (cis-1,2-difluoroethene): This molecule contains carbon, hydrogen, and fluorine. The C-F bonds have unequal electron distribution due to the electronegativity difference. Furthermore, the arrangement of atoms in cis-1,2-difluoroethene results in an overall molecular dipole.
Based on the analysis, the substances that have a molecular dipole are: CHF3 (fluoroform), H2NCH2CH2OH (ethanolamine), (CH3)3N (trimethylamine), and CHFCHF (cis-1,2-difluoroethene). Therefore, the correct answer is: CHF3, H2NCH2CH2OH, (CH3)3N, and CHFCHF.