Question

The list below represents some elements of the periodic table: chlorine, helium, phosphorus, magnesium, and cesium.

Choose from the above and answer the following question: Most electronegative element.

Answer 1

Electronegativity: When two atoms are bonded via a covalent bond formed by sharing a pair of electrons, then the tendency of an atom to attract the shared pair of electrons towards itself is known as electronegativity. The more strongly the atom pulls the shared pair of electrons towards itself, the more electronegative is the element.

1. The trend of electronegativity in the Group:

Going down the group, the size of the atom increases, and thus the distance between the shared electrons and nucleus also increases which leads to a decrease in the pull of the nucleus on the electrons. Hence, electronegativity decreases on moving down the group.

2. The trend of electronegativity across the period:

As we move from left to right, there is an increase in the number of protons in the nucleus and thus the nucleus attracts the shared pair of electrons more strongly. Hence, electronegativity increases from left to right.

3. The most electronegative element from the given elements:

1. From the given elements, Chlorine ($\mathrm{Cl}$) belongs to group 17, Helium ($\mathrm{He}$) belongs to group 18, Phosphorus ($\mathrm{P}$) belongs to group 15, magnesium ($\mathrm{Mg}$) belongs to group 2, and Cesium ($\mathrm{Cs}$) belongs to group 1.
2. Helium ($\mathrm{He}$) is a noble gas with zero electronegativity due to its filled valence shell. Then after Helium, Chlorine ($\mathrm{Cl}$) belongs to the extreme right side of the periodic table and as it lacks only one electron to complete its valence shell, the chlorine will strongly attract the shared pair of electrons towards itself to complete its octet. Hence, Chlorine is the most electronegative atom.

Chlorine is the most electronegative element.