What is electronegativity? Explain its periodicity in the periodic table.

Electronegativity:
- The tendency of an atom in a chemical compound to attract a shared pair of electrons towards itself is known as electronegativity.
$\rightarrow$ It is not a directly measurable quantity.
$\rightarrow$ Linus Pauling,an American scientist,in $1922$ assigned an arbitrary value of $4.0$ to fluorine.
Periodicity:
- As we move from left to right in a period,electronegativity increases due to an increase in effective nuclear charge and a decrease in atomic size.
Example: Second Period

Element	Electronegativity
$Li$	$1.0$
$Be$	$1.5$
$B$	$2.0$
$C$	$2.5$
$N$	$3.0$
$O$	$3.5$
$F$	$4.0$

- As we move from top to bottom in a group,electronegativity decreases due to an increase in atomic size and shielding effect.
Example: Group-$17$

Element	Electronegativity
$F$	$4.0$
$Cl$	$3.0$
$Br$	$2.8$
$I$	$2.5$
$At$	$2.2$