 Electrons
are the negatively charged part
of the atom
 Electrons are found in orbitals around the
nucleus
 We write the electron configuration of the
element to see the different orbitals the
electrons are located in
 Write
the electron configuration for
Lithium…
 Write
the electron configuration for
Fluorine…
 The
electrons in the last energy level of
the element are the VALENCE electrons
 The last energy level is the part of the
configuration that has the largest number
in front of it
Lithium = 1s2 2s1
Fluorine = 1s2 2s22p5
 An
element can have anywhere from 1-8
valence electrons
 The number of valence electrons
determines how REACTIVE the element is
 8 = totally unreactive
 1 and 7 = extremely reactive
 2 and 6 = pretty reactive
 3-5 = only kinda reactive
Pull out your periodic table!
You can find the valence electron of the
element by seeing what group it is in….
Where are the groups on the periodic
table?
You should already have groups 1-18 listed
on your periodic table
Group 1 = 1 Valence Electron
Group 2 = 2 Valence Electrons
Group 13 = 3 Valence Electrons
Group 14 = 4 Valence Electrons
Group 15 = 5 Valence Electrons
Group 16 = 6 Valence Electrons
Group 17 = 7 Valence Electrons
Group 18 = 8 Valence Electrons
 The
transition metals in groups 3-12 have
their own set of rules
 Don’t
worry about them for now
 Write
down the following elements on a
sheet of paper… next to them find out
how many valence electrons they have?
1. Neon 2. Sodium 3. Aluminum
4. Calcium 5. Sulfur 6. Iodine 7. Carbon
8. Lead
9. Phosphorus 10. Krypton
 How
many valence electrons does
Arsenic have?
 How
many valence electrons does
Potassium have?
 To
find the number of valence electrons
for the elements in groups 1,2 and 13-18
you look at your periodic table
 Transition
metals (groups 3-12) have
their own rules
 To
find the number of valence electrons
for a transition metal you have to write
the shorthand electron configuration for
that metal
 For
example… Iron’s shorthand electron
configuration is [Ar] 4s2 3d6
 Just
like the regular valence electrons, we
look at the highest energy level
 Iron’s
shorthand electron configuration is
[Ar] 4s2 3d6
4s2 = highest energy level
 Iron
has 2 valence electrons

All transition metals will have a
shorthand configuration that gives you 2
valence electrons
 However, Transition
Metals can act like
they have anywhere from 1-4 electrons
“Valence Electrons” side of worksheet
For each question you should
1. Write the shorthand electron
configuration
2. Write how many valence electrons each
element has
 By
now we know that an element can
have anywhere from 1-8 valence
electrons
 We
can find the number of valence
electrons the element has by looking at
the periodic table or by its electron
configuration
 For
Groups 1,2, 13-18 the number of
valence electrons depends on group it is
in
• Exception! Helium is a noble gas and is full, but
because of its electron configuration it has 2
valence electrons, not 8
 Transition
metals in groups 3-12 all have
2 valence electrons, even though they
don’t always act that way
 We
can draw Lewis Structures to
represent the valence electrons of an
element
To draw a Lewis Structure
1. Put the element symbol in the middle
2. Determine how many valence electrons
it has
3. Draw a dot for each electron around the
symbol
 As
you are putting the dots around the
symbol you start by putting one dot on
each side of the symbol
 No side should ever have more than 2
dots
Example: Electron dot diagram for Carbon
: C:
C
Draw the electron dot diagram
1. Put the element symbol in the middle
2. Determine how many valence electrons
it has
3. Draw a dot for each electron around the
symbol
Na
Cl
Mg
Ar
 “Lewis
Dot Diagrams” side of worksheet
 Remember, Helium
is an exception to the
noble gases, it only has 2 valence
electrons!