HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge
1
neutron
No charge
1
electron
-ve charge
nil
ATOMIC STRUCTURE
He
2
4
Atomic number
the number of protons in an atom
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or
Shells around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
ATOMIC STRUCTURE
Three ways to represent the atomic structure of an
element or compound;
1. Lewis Notation
2. Rutherford-Bohr Model
3. The Ball and Stick Model
Determine the number of shells and the
number of valence electrons for:
2nd Period = 2 shells
4th Group =
4 valence
electrons
Determine the number of shells and the
number of valence electrons for:
3rd Period = 3 shells
1st Group =
1 valence
electron
Name the element.
Number of shells ?
Valence electrons ?
Write your answers on your
handout.
Name the element.
Number of shells ?
Valence electrons ?
Neon
2nd Period = 2 shells
8th Group = 8 valence
electrons
Name the element.
Number of shells ?
Valence electrons ?
Name the element.
Number of shells ?
Valence electrons ?
Potassium
4th Period = 4 shells
1st Group = 1 valence
electron
Name the element.
Number of shells ?
Valence electrons ?
Name the element.
Number of shells ?
Valence electrons ?
Helium
1st Period = 1 shell
8th Group = 2 valence
electrons
• Helium is the exception in Group 8.
• Since it has just one shell, that shell
can only fit 2 electrons instead of 8.
• It is in this group because all the
elements have a full outer shell.
Lewis Electron Dot Diagrams
Invented by the American chemist, G.N.
Lewis.
1. Write the chemical symbol
2. Write the appropriate number of dots in a
clockwise manner
Lewis Structures
1) Write the element
symbol.
2) Carbon is in the 4th
group, so it has 4
valence electrons.
3) Starting at the right,
draw 4 electrons, or
dots, counterclockwise around the
element symbol.
Lewis Structures
1) Check your work.
2) Using your periodic
table, check that
Carbon is in the 4th
group.
3) You should have 4
total electrons, or
dots, drawn in for
Carbon.
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
On your worksheet, try
these elements on your
own:
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
Lewis Structures
a)
b)
c)
d)
e)
f)
H
P
Ca
Ar
Cl
Al
BOHR-RUTHERFORD DIAGRAMS
Bohr-Rutherford diagrams should be drawn
using the following steps:
 Draw the nucleus with the proper
number of protons (+1) and neutrons
(0).
 Draw the first electron shell with the
appropriate number of electrons (-1).
BOHR-RUTHERFORD DIAGRAMS
 Draw the second valence shell (if
applicable) with the appropriate number
of electrons (-1).
 Continue to draw valence shells with
electrons until you have the proper
number of electrons for the element.
Example: sulfur
EXAMPLES
• Draw the BohrRutherford Diagram
for:
•Mg & Ca
Magnesium (Mg) and calcium (Ca)