Question

Which of the following is most electronegative?
A. F
B. Cl
C. Br
D. I

Answer 1

The periodic table is made in such a form that it can show the variations of several properties of the atoms both along the period and down the group. So, there is also a trend for electronegativity both across the period and down the group.

Complete step by step answer:
-There are 7 periods and 18 groups in periodic table where atoms are arranged in the increasing order of their atomic number because the atomic number gives us the number of electrons of the atom. Electrons only decide the chemical properties of an atom as they are loosely held by the atom.
-Electronegativity can be defined as the tendency of an atom to attract the pair of electrons which is shared in a bond towards itself. More is the electron affinity of an atom towards an electron, more is its electronegativity.

-Along the period, the atomic number increases and so does the number of electrons without altering the number of shells of atoms. Thus, the electronegativity increases across the period. This can be explained on the basis of increase in ionization energy also.

-Down the group, the number of shells increase but the valence electrons remain the same. Atomic size increases down the group. This increases the distance between the nucleus of an atom to the valence electrons. Thus, the electronegativity decreases down the group.

-Thus according to this order, we see that the group 17 elements are the most electronegative and among them, the strength decreases down the group. It is due to the increase in the electron density as we go down the group.

-We can also see it in this way. The electronic configuration of group 17 has only 1 electron less to attain the configuration of noble gases. So the elements of group 17 try to achieve stable state by gaining electrons and thus are most electronegative.

-In the options given, we can see that all of the elements belong to group 17. Thus the atom which is at the top of its group will be most electronegative in nature as it will have the least electron density and so will be more keen to attract an electron towards itself to become stable.
So, the correct answer is “Option A”.

Note: Electronegativity of atoms is measured by Pauling scale. According to that scale, F is the most electronegative element of the periodic table. It is succeeded by O and then N. Value of electronegativity for F = 4.0, O = 3.5 and N = 3.0. Cl also has the value equal to N but it is less electronegative than N though theoretically, we write Cl to be more electronegative than N.