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Trends in Electronegativity

Key Concepts

In 1932 Linus Pauling defined electronegativity as the power of an atom in a molecule to attract electrons to itself.
Pauling devised a numerical electronegativity scale, based on bond energies.
In general, electronegativities decrease down a Group of the Periodic Table.
In general, electronegativities increase going from left to right across a Period of the Periodic Table.

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Trends in Electronegativities in Groups of the Periodic Table

In general, the electronegativities of the elements in a Group decrease as you go down the group from top to bottom.
As the atomic radius increases and the number of completed electron shells (energy levels) increases going down the group, the power of the atom's nucleus to attract electrons to itself decreases.

Group 1 (IA, Alkali Metals)

Element	Atomic Number (Z)	Symbol	Electronegativity	Trend
lithium	3	Li	0.98	(highest) \|	Electronegativity decreases down Group 1 as atomic radius increases number of inner electron shells increases.
sodium	11	Na	0.93	\|
potassium	19	K	0.82	\|
rubidium	37	Rb	0.82	\|
cesium	55	Cs	0.79	\|
francium	87	Fr	0.7	\/ (lowest)

Group 17 (VIIA, Halogens)

Element	Atomic Number (Z)	Symbol	Electronegativity	Trend
fluorine	9	F	3.98	(highest) \|	Electronegativity decreases down Group 17 as atomic radius increases number of inner electron shells increases.
chlorine	17	Cl	3.16	\|
bromine	35	Br	2.96	\|
iodine	53	I	2.66	\|
astatine	85	At	2.2	\| \/ (lowest)

Trends in Electronegativity in Periods of the Periodic Table

In general, electronegativities of the elements in the same Period increases as you go from left to right across the period.
As the nuclear charge increases and the atomic radius decreases across a period, the power of the atom's nucleus to attract electrons to itself increases.

Period 2

Element	Li	Be	B	C	N	O	F
Atomic Number (Z)	3	4	5	6	7	8	9
Electronegativity	0.98	1.57	2.04	2.55	3.04	3.44	3.98
General Trend	(lowest)-	-----	-----	-----	-----	---->	(highest)
General Trend	Electronegativity increases across Period 2 as nuclear charge increases and atomic radius decreases.

Period 3

Element	Na	Mg	Al	Si	P	S	Cl
Atomic Number (Z)	11	12	13	14	15	16	17
Electronegativity	0.93	1.31	1.61	1.9	2.19	2.58	3.16
General Trend	(lowest)-	-----	-----	-----	-----	---->	(highest)
General Trend	Electronegativity increases across Period 3 as nuclear charge increases and atomic radius decreases.

Practice Questions

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