(a) Electropositive nature of the element(s) increases down the group and decreases across the period. (b) Electronegativity of the element decreases down the group and increases across the period. (c) Atomic size increases down the group and decreases across a period (left to right). (d) Metallic character increases down the group and decreases across a period. On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers $ 3 $ to $ 9. $ Name the most electronegative element: (A) Lithium (B) Boron (C) Oxygen (D) Fluorine
Hint: The atomic numbers of Lithium, Boron, Oxygen and Fluorine is between $ 3 $ and $ 9; $ they are as follows - Lithium has atomic number $ 3, $ Boron has atomic number $ 5, $ Oxygen has atomic number $ 8, $ and Fluorine has atomic number $ 9. $ Using this information and applying the trend of electronegativity, we can easily find out the answer.
Complete answer: Electronegativity is the tendency of an element to attract a shared pair of electrons to itself. According to the periodic trend regarding electronegativity, it is said that electronegativity of the element decreases down the group, and increases across the period. Lithium, Boron, Oxygen and Fluorine lie on the same period, which is period $ 2. $ In accordance with the trend, the element lying at the end of that period, meaning furthest to the right in that period, will have the highest electronegativity. Comparing the four elements that we have taken under consideration, Fluorine lies on second last from the right on this period, and hence has the highest electronegativity. Therefore, the required answer is (D) Fluorine.
Note: The periodic table is a tabular depiction of all the chemical elements known to man. The table is also referred to as the periodic table of elements. The arrangement of the elements in the periodic table is in accordance with atomic numbers, repeating chemical properties and electronic configuration. There are several patterns noticed in the table and they have been called “trends”. Some important periodic trends are electronegativity, atomic radii, metallic character, ionization energy et cetera.