ELECTRONEGATIVITY

By: Sahaya Asirvatham

Linus Pauling

Linus Pauling, an

American chemist (and

winner of two Nobel

prizes!) came up with the

concept of

electronegativity in 1932

to help explain the nature

of chemical bonds.

Electronegativities of Some Elements

Element Pauling scale F 4.0 Cl 3.0 O 3.5 N 3.0 S 2.5 C 2.5 H 2.1 Na 0.9 Cs 0.7

Based on

BOND

DISSOCIATION

ENERGY

Electronegativities

Looking across a row or down a group of the

periodic table we can see a trend in values.

Mulliken Scale

R.S. Mulliken proposed electronegativity scale , in

which the Mulliken electronegativity, ΧM

is related to the

electron affinity EAv (a measure of the tendency of an

atom to form a negative species) and

ionization potential IEv (a measure of the tendency of

an atom to form a positive species)

by the equation:

ΧM = (IEv + EAv)/2

Ionic size

Metallic elements easily lose electrons.

Non-metals more readily gain electrons.

How does losing or gaining an electron effect

the size of the atom (ion) ?

Positive ions

Positive ions are always smaller that the

neutral atom. Loss of outer shell electrons.

Negative Ions

Negative ions are always larger than the

neutral atom. Gaining electrons.

Ionic or Covalent Bonds?????

Salt crystals are repeating patterns of positive+ cations and

negative- anions held together by electrostatic attraction.

IONIC COMPOUNDS

COVALENT COMPOUNDS

Biological molecules are covalently bound Most consist of the non-metals Carbon, Oxygen, Hydrogen, and

Nitrogen.

SO…..

Ionic and covalent bonds are very different,

but how do we predict if a bond will be ionic

or covalent?

electronegativity The ELECTRONEGATIVITY of an element

helps us understand the difference between

ionic and covalent bonding

Electronegativity is the measure of the ability of an atom in a bond to attract electrons.

Elements with a HIGH electronegativity

have a STRONG pull on electrons.

Elements with a LOW electronegativity

have a WEAK pull on electrons.

When two atoms form a bond their DIFFERENCE in

electronegativity determines the bond type.

A large difference in electronegativity means one

atom will win the “tug of war” and take the electrons

completely.

This is an ionic bond.

When the electronegativity of two

bonding atoms is very similar, neither atom

wins the “tug of war” and the electrons are

shared equally.

This produces a covalent bond

In a true covalent bond

electrons are shared equally

IONIC COVALENT

Transfer electrons Share electrons

Between an atom of

high electronegativity

and an atom of low

electronegativity

Between two atoms

of equal or very

close

electronegativities

NaCl N2