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# Classification of Elements And Periodicity In Properties ## The Main Group Elements - Group 0 - He - Ne - Ar - Kr - Xe - Rn ## Electronegativity ### Ability to attract electrons. Approximate values for the electronegativity of a few elements are given in Table 3.8(a): The electronegativity of a...

# Classification of Elements And Periodicity In Properties ## The Main Group Elements - Group 0 - He - Ne - Ar - Kr - Xe - Rn ## Electronegativity ### Ability to attract electrons. Approximate values for the electronegativity of a few elements are given in Table 3.8(a): The electronegativity of any given element is not constant; it varies depending on the element to which it is bound. Though it is not a measurable quantity, it does provide a means of predicting the nature of force that holds a pair of atoms together—a relationship that you will explore later. ### Trends In Electronegativity - Electronegativity generally increases across a period from left to right (say from lithium to fluorine) and decreases down a group (say from fluorine to astatine) in the periodic table. - Can the electronegativity be related to atomic radii, which tend to decrease across each period from left to right, but increase down each group? The attraction between the outer (or valence) electrons and the nucleus increases as the atomic radius decreases in a period. The electronegativity also increases. ## Table 3.8(a) Electronegativity Values (on Pauling scale) Across the Periods Atom (Period II) | Li | Be | B | C | N | O | F ------- | -------- | -------- | -------- | -------- | -------- | -------- | -------- Electronegativity | 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | 4.0 ## Table 3.8(b) Electronegativity Values (on Pauling scale) Down a Family Atom (Group 1) | Value | Atom (Group 17) | Value ------- | -------- | -------- | -------- Li | 1.0 | F | 4.0 Na | 0.9 | Cl | 3.0 K | 0.8 | Br | 2.8 Rb | 0.8 | I | 2.5 Cs | 0.7 | At | 2.2 ### On the same account electronegativity values decrease with the increase in atomic radii down a group. The trend is similar to that of ionization enthalpy. ### Knowing the relationship between electronegativity and atomic radius, can you now visualise the relationship between electronegativity and non-metallic properties? Non-metallic elements have strong tendency.