How is it called the effect of electronegative atoms on their neighbours?

Electronegativity is conceived to be the ability of an atom involved in a chemical bond to polarize electron density towards itself. There are various scales of which the #"Pauling Scale"# was the earliest, and is still most widely used. Pauling originally used ionization, and atomization energies, measurable atomic properties, whose values he then normalized to give a scale that varied between #0-4#...

And so in a chemical bond, #H-F#, or even, #H_2O#,,,we could write in the dipoles, the charge separation as....

#stackrel(delta^+)H-stackrel(delta^-)F# or #stackrel(delta^+)H-stackrel(delta^-)O-stackrel(delta^+)H#

...on the basis that the electronegativity of hydrogen, #2.2#, is LESS than that of fluorine, #4.0#, or oxygen, #3.54#...the heteroatoms denude the hydrogen atoms of electronic charge, and acquire a PARTIAL NEGATIVE CHARGE....

Electronegatvity INCREASES ACROSS A PERIOD, from left to right as we face the Table. and DECREASES down a Group, a column of the Periodic Table.

Why so? Well, incomplete electronic shells shield the nuclear charge VERY imperfectly...and this is certainly REFLECTED in the well known diminution of atomic radii ACROSS the Period from left to right. And so the larger the atomic number for a given Period, the greater should be its electronegativity.