Question

What is the element with the lowest electronegativity value? How do you determine this?
A. Cesium
B. Helium
C. Calcium
D. Fluorine

Answer 1

Hint: The electronegativity of the atom is defined as its tendency to attract the electrons from the other atoms which have been shared in a bond. So on moving left to right in the periodic table the electronegativity of the atoms increases. Whereas the electronegativity decreases from top to bottom in the group.

Complete step by step answer:
- The metals usually have low electronegativity value as compared to the non metals. This is so because in the metals the number of valence electrons are less so they try to increase their stability by losing their electrons thereby forming the cations whereas the non metals have more valence electrons so they try to stabilise by adding electrons.
- The most electronegative elements are those which need few electrons for completing their valence shell and also have least quantity of the inner electrons shells between the nucleus and the valence electrons. It has the atomic number of 17. So such an element is fluorine in the given option whose electronegativity is 4.0.
- Whereas the cesium has the lowest electronegativity value as it is the most alkaline element and tends to lose its single valence electron readily to form the stable element. It has the atomic number of 55.
- It has eight numbers of shells between the nucleus and the valence electrons. So it has a large size and we know that the electronegativity of the atom is inversely proportional to its size. Hence the electronegativity of cesium is the lowest. The electronegativity of cesium is 0.659. Whereas the atomic number of helium is 2 as it has only one shell and the atomic number for calcium is 20.
- The electronegativity of helium is not listed by the Pauling electronegativity scale. The electronegativity value for calcium is 1. So the highest atomic number is of cesium with 8 shells between nucleus and valence electrons and tends to give its electrons readily, so it has the lowest electronegativity.

Hence the correct answer is option A.

Note: The electronegativity affects the strength of the covalent bond formed between the two atoms. The homonuclear diatomic molecules have a pure covalent bond because the electronegativities of the bonded atoms are the same. Whereas if the electronegativity got varied between the two species the covalent bond would get polarised.