Which of these molecules is most polar?
Ethyl-fluoride would be the most polar since there is the highest difference in electronegativities between the adjacent functional groups (ethyl and fluorine).
Here is why:
1) H3C-CH3: a non-polar molecule, becz the difference of electronegativity between H and C is very small. H-C covalent bond is non-polar. The molecule itself is non-polar
2) As 4 the next four molecules: the only difference between them is the "halogen group" attached to the end of the molecule.
Obviously, this is a type of Q testing 4 ur understand for electronegativity and in relation to molecular polarity
Three things 2 know:
a) Definition for electronegativity (what does it mean)..
electronegativity is defined as the electron attracting power OF an atom IN a molecule FOR the bonding electrons.
ie.. one has higher electronegativity will tend to attract the bonding electrons to itself more than the adjacent atom. As a result, this produces a permanent dipole moment in between the atoms. Hence the covalent bond is POLAR.
2) The trend of electronegativity across the period and up a group:
The electronegativity INCREASES acrss a period and up a group. Another words, Fluorine has the HIGHTEST electronegativity than any other elements in the periodic table.
3) Polar bond can be further categorized into: weakly polar, moderate polar, strongly polar depending on the electronegativity differences.
Ones with the largest electronegativity differences produce most polar bond.
In this given Q. the electronegativity trend for group 17 is like this: F > Cl > Br > I
Hence H3C-CH2-F is the most polar molecule compares to the other ones.
ch3-ch2-f because f is the most electronegative