What do chemists mean by the term electronegativity? what does its electronegativity tell us about the atom?

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegativeat 0.7.

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1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged