Shorthand electron
configuration

 Na
Normal
2 2s2 2p6 3s1
◦
1s
electron
configuration  Ca
◦ 1s2 2s2 2p6 3s2 3p6 4s2

 Shortcut of electron
Shorthand
configuration using noble
electron
configuration gases
 Na
◦ [Ne] 3s1

Ca
◦ [Ar] 4s2

What are
Ions?



Atoms can gain or
lose electrons.
If an atom gains or
loses electrons, it will
obtain a charge
Ions are charged
atoms.
 Cations
 If
Na lost an
electron what
is its charge?
 If Ca lost 2
electrons what
is its charge?
Atoms with a
positive charge
 Atoms that have
lost electrons


Na+

Ca
2+


Anions
If S gains two
electrons,
what is its
charge
Atoms with a
negative charge
 Atoms that have
gained electrons


S2-
 What
is a
valence
electron?

Valence electrons are the
electrons in the highest
occupied energy level of
an element’s atoms.
◦ Cl = 1s2 2s2 2p6 3s2 3p5
◦ Cl has 7 electrons in its
last energy shell.

Number of valence
electrons largely
determines the chemical
properties of an element.

What is a
valence
electron?

Valence electrons are also
related to the group
numbers of the periodic
table.
◦ 1A
◦ 2A
◦ 3A
◦ 4A
◦ 5A
◦ 6A
◦ 7A
◦ 8A

--- 1 valence electron
--- 2 valence electrons
--- 3 valence electrons
--- 4 valence electrons
--- 5 valence electrons
--- 6 valence electrons
--- 7 valence electrons
--- 8 valence electrons
Helium is the exception
It has 2 valence electrons


Valence
electrons
What is the
electron dot
structure of
S?
Valence electrons are
usually the only
electrons used in
chemical bonds.
 Valence electrons are
usually shown in
electron dot structures.
 Example: Ca


Ca :

..
:S:

The Octet
Rule
In forming compounds,
atoms tend to achieve
the electron
configuration of a
noble gas.
 Octet = a set of eight
ns2 np6

What is a
Cation?
 Metals

Cations are atoms with a
positive charge
 Metals tend to become
cations.
 Metals tend to lose their
valence electrons,
leaving a complete octet
in the next-lowest
energy level.


Nonmetals
Nonmetals tend to gain
electrons since they
have their last energy
level almost full, it is
easier to gain electrons
than to lose them.
 Nonmetals tend to form
anions

◦ Anions are atoms with a
negative charge