Video Transcript
By considering the Pauling scale,
used to quantify electronegativity, which of the following elements is the least
electronegative? (A) Cesium, (B) sodium, (C)
rubidium, (D) potassium, or (E) lithium.
Electronegativity values describe
the tendency of an atom to withdraw electron density from a chemical bond. Electron density tends to be higher
around the bonded atom that has the higher electronegativity number. The figure shows how electron
density is higher about the more electronegative atom of a covalent bond. While many scientists have devised
methods for quantifying electronegativity numbers, all of the proposed methods
generate similar numbers.
Linus Pauling proposed a very
famous method for determining the electronegativity number of elements. This method determines
electronegativity numbers from bond dissociation data, which is the energy data
obtained when measuring the dissociation of a covalent bond. Scientists have determined the
Pauling electronegativity number for most of the chemical elements. And this figure shows these numbers
for the listed alkali metals.
The numbers become smaller as we
move from the top of the group to the bottom, and we can understand the trend of
electronegativity numbers if we consider the relationship between atomic size and
electronegativity. Atoms effectively withdraw a lot of
electron density if they are small because their positively charged protons are
close to the electrons of the bond. Larger atoms are less effective at
withdrawing electron density because their protons are further apart from the
electrons of the chemical bond. And so, there is a relatively weak
force of attraction between the atomic nucleus of a large atom and the electrons of
its bond.
Atomic radius, which we typically
use to represent atomic size, tends to increase with atomic number. Since the atomic radius becomes
increasingly large down a group in the periodic table, these larger atoms will have
a weaker interaction with the electrons of the bond. The element cesium has the highest
atomic number of all the listed alkali metals. It is close to the bottom left of
the periodic table and has a larger diameter than all the other listed elements. And it also has the lowest Pauling
electronegativity number.
And with all of this information,
we can revisit and answer the question. By considering the Pauling scale,
used to qualify electronegativity, which of the following elements is the least
electronegative? And the correct answer is answer
choice (A), cesium.
