Final answer:
The non-polar molecule among the options is CF4, as it has a symmetrical tetrahedral geometry where the individual dipole moments caused by fluorine atoms cancel out.
Step-by-step explanation:
To determine which of the listed molecules is non-polar, we must examine their geometry and the electronegativity of the atoms involved. For a molecule to be non-polar, it must have a symmetric distribution of electrons and cannot have a net dipole moment.
- NH3 (ammonia) is polar because it has a trigonal pyramidal shape with a lone pair on the nitrogen atom, creating a dipole moment.
- CF4 (carbon tetrafluoride) is non-polar despite the presence of highly electronegative fluorine atoms because it has a tetrahedral geometry where the dipole moments cancel out due to symmetry.
- CH2F2 (dichlorodifluoromethane) is polar as the presence of different atoms causes the molecule to have an uneven distribution of electron density.
- HCN (hydrogen cyanide) is also polar due to the difference in electronegativity between hydrogen, carbon, and nitrogen, resulting in a dipole moment.
- He (helium) is not a molecule but an atomic element and is non-polar.
Therefore, the non-polar molecule among the options provided is CF4.