Which of the following molecules is polar?
1. CH4
2. BH3
3. NH3
4. CF4
5. H2
To determine if a molecule is polar, you need to consider its molecular geometry and the polarity of its bonds.
1. CH4 (methane) - This molecule consists of a central carbon atom bonded to four hydrogen atoms. Since carbon and hydrogen have similar electronegativities, the bonds are nonpolar. Additionally, the molecular geometry of CH4 is tetrahedral, which means the bond dipoles cancel each other out, making the molecule nonpolar.
2. BH3 (boron trifluoride) - This molecule has a central boron atom bonded to three hydrogen atoms. Boron is less electronegative than hydrogen, so the B-H bonds are polar. However, the molecular geometry of BH3 is trigonal planar, with the hydrogen atoms at the corners of an equilateral triangle. The bond dipoles in BH3 are symmetrically arranged, which cancels out the polarity, making the molecule nonpolar.
3. NH3 (ammonia) - This molecule consists of a central nitrogen atom bonded to three hydrogen atoms. Nitrogen is more electronegative than hydrogen, so the N-H bonds are polar. The molecular geometry of NH3 is pyramidal, resulting in an asymmetric distribution of the bond dipoles. Thus, ammonia is a polar molecule.
4. CF4 (carbon tetrafluoride) - This molecule has a central carbon atom bonded to four fluorine atoms. Carbon and fluorine have a significant electronegativity difference, making the C-F bonds highly polar. However, the tetrahedral molecular geometry of CF4 means the bond dipoles point towards the corners of the tetrahedron, cancelling each other out. Thus, CF4 is a nonpolar molecule.
5. H2 (hydrogen) - This molecule consists of two hydrogen atoms bonded together. Since hydrogen and hydrogen have the same electronegativity, the H-H bond is nonpolar. The molecule is symmetric, making it nonpolar.
Therefore, the polar molecule among the options is NH3 (ammonia).
To determine whether a molecule is polar or nonpolar, we need to analyze its molecular geometry and the polarity of its bonds.
1. Methane (CH4): This molecule consists of four hydrogen atoms bonded to a carbon atom. Since carbon and hydrogen have similar electronegativities, the carbon-hydrogen bonds are considered nonpolar. Additionally, the molecule has a symmetrical tetrahedral shape, with the carbon atom at the center and the hydrogen atoms surrounding it. The vector sum of the dipole moments cancels out, resulting in a nonpolar molecule.
2. Borane (BH3): This molecule consists of three hydrogen atoms bonded to a boron atom. Boron is less electronegative than hydrogen, so the boron-hydrogen bonds are considered polar. However, the molecule has a trigonal planar shape, with the boron atom at the center and the hydrogen atoms surrounding it. The vector sum of the dipole moments does not cancel out, leading to a polar molecule.
3. Ammonia (NH3): This molecule consists of three hydrogen atoms bonded to a nitrogen atom. Nitrogen is more electronegative than hydrogen, so the nitrogen-hydrogen bonds are considered polar. The molecule has a pyramidal shape, with the nitrogen atom at the apex and the hydrogen atoms in a triangular base. The vector sum of the dipole moments does not cancel out, resulting in a polar molecule.
4. Tetrafluoromethane (CF4): This molecule consists of four fluorine atoms bonded to a carbon atom. Carbon is less electronegative than fluorine, so the carbon-fluorine bonds are considered polar. However, the molecule has a symmetrical tetrahedral shape, with the carbon atom at the center and the fluorine atoms surrounding it. The vector sum of the dipole moments cancels out, resulting in a nonpolar molecule.
5. Hydrogen (H2): This molecule consists of two hydrogen atoms bonded together. Hydrogen has similar electronegativity values, so the hydrogen-hydrogen bonds are considered nonpolar. Additionally, with a linear shape, the vector sum of the dipole moments cancels out, resulting in a nonpolar molecule.
Based on this analysis, the only polar molecule is NH3 (Ammonia).
To be polar, molecules must have the following:
1. There must be a difference in electronegativity between the central element and the binding element(s).
2. The molecules must NOT be symmetrical.
CH4, for example, has a small difference in EN between C and H, but it is tetrahedral which makes it symmetrical and the CH4 molecule as a whole has no dipole moment.