Vocabulary:
1. valence shell
2. valence electrons
3. anion
4. cation
5. isoelectric
6. Lewis structure (Lewis
dot diagram)
Banksy, British, 2002
Pauling Electronegativities
 Linus Pauling developed
the concept of
electronegativity and
assigned values to atoms
to quantify
electronegativity.
 Electronegativities have
no units; they are
comparative only.
chlorine
potassium
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s ___3p ___ ___ ___
3s ___3p ___ ___ ___
2s ___2p ___ ___ ___
2s ___2p ___ ___ ___
1s ___
1s ___
17 protons
19 protons
chlorine
potassium
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s ___3p ___ ___ ___
3s ___3p ___ ___ ___
2s ___2p ___ ___ ___
2s ___2p ___ ___ ___
1s ___
1s ___
17 protons
19 protons
chlorine
But a whole
new energy
level
potassium
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s ___3p ___ ___ ___
3s ___3p ___ ___ ___
2s ___2p ___ ___ ___
2s ___2p ___ ___ ___
1s ___
1s ___
17 protons
Only 2 more
protons 
19 protons
chlorine
That means strong
attraction for these
valence electrons
(large Zeff).
potassium
And weak attraction
for this valence
electron (low Zeff).
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s ___3p ___ ___ ___
3s ___3p ___ ___ ___
2s ___2p ___ ___ ___
2s ___2p ___ ___ ___
1s ___
1s ___
17 protons
19 protons
chlorine
That means easy to gain 1
more electron here (high
electronegativity)
potassium
And easy to lose an
electron here (low
ionization energy)
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s ___3p ___ ___ ___
3s ___3p ___ ___ ___
2s ___2p ___ ___ ___
2s ___2p ___ ___ ___
1s ___
1s ___
17 protons
19 protons
chlorine
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___
2s___2p ___ ___ ___
1s ___

Elements that have a
nearly full valence
shell, like chlorine,
have high
electronegativities
and can gain
electrons easily.
17 protons and 17 electrons = 0 charge
chlorine
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___
2s___2p ___ ___ ___
1s ___

Elements that have a
nearly full valence
shell, like chlorine,
have high
electronegativities
and can gain
electrons easily.
17 protons and 18 electrons = 1- charge
chlorine
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___

Atoms that have gained
one or more electrons
are now negative ions
and are called anions
(ˈan-ī-ən).
2s___2p ___ ___ ___
1s ___
17 protons and 18 electrons = 1- charge
potassium
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___
2s___2p ___ ___ ___
1s ___

Elements that have a
nearly empty valence
shell, like potassium,
have low
electronegativities
and can lose
electrons easily.
19 protons + 19 electrons = 0 charge
potassium
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___

Atoms that have lost
one or more electrons
are now positive ions
and are called cations
(kat-ī-ən).
2s___2p ___ ___ ___
1s ___
19 protons + 18 electrons = 1+ charge
chlorine anion (1- charge)
potassium cation (1+ charge)
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___
3s___3p ___ ___ ___
2s___2p ___ ___ ___
2s___2p ___ ___ ___
1s ___
1s ___
When each atom gained or lost electrons, the new
outer shell (energy level) is full, like the noble gases.
chlorine anion (1- charge)
potassium cation (1+ charge)
4s __ 4p ___ ___ ___
4s __ 4p ___ ___ ___
3s___3p ___ ___ ___
3s___3p ___ ___ ___
2s___2p ___ ___ ___
2s___2p ___ ___ ___
1s ___
1s ___
Different atoms or ions that have the same electron
configuration are called isoelectric. The Cl- ion is isoelectric
with the K+ ion. They are both isoelectric with neon.
Atoms lose or gain electrons in order
to have a full valence shell (a noble
gas configuration). This will typically
result in 8 valence electrons and
make the resulting ion isoelectric
with the noble gas.
Rather than draw orbital diagrams, we can use Lewis Structures
(Lewis Dot Diagrams) to show numbers of valence electrons.
1.
2.
3.
Write symbol of
element.
Determine number of
valence electrons by
position on periodic
table
Use dots to represent
electrons around
symbol (one at a time
on each side and
then pair them up.)
7 valence electrons
because in group 17
Cl
So when chlorine
forms an ion, will it
gain or lose electrons?
How many?
It needs one more
to have an octet.
Cl
1-
What will its charge be now?
1.
2.
3.
Write symbol of
element.
Determine number of
valence electrons by
position on periodic
table
Use dots to represent
electrons around
symbol (one at a time
on each side and
then pair them up.)
1 valence electrons
because in group 1
K
So when potassium
forms an ion, will it
gain or lose electrons?
How many?
It will lose one
electron to have
a full valence
K
1+
What will its charge be now?
1.
2.
3.
Write symbol of
element.
Determine number of
valence electrons by
position on periodic
table
Use dots to represent
electrons around
symbol (one at a time
on each side and
then pair them up.)
5 valence electrons
because in group 15
N
So when nitrogen
forms an ion, will it
gain or lose electrons?
How many?
It will gain
three electrons
to have a full
valence
N
3-
What will its charge be now?

Using periodic trends, we can predict the ion
charge for the main group elements.
1+
0
2+
3+ 4+/- 3- 2- 1-