Lewis Dot Structure

1. AIM: How to write Lewis Dot
Structures (Electron Dot Structures)
DO NOW:
1. WRITE THE ELECTRON CONFIGURATION FOR THE PHOSPHORUS
ATOM IN THE GROUND STATE.
2. THE PHOSPHORUS ATOM GAINS 3 ELECTRONS TO FORM AN ION.
WRITE THE NEW CONFIGURATION.
3. COMPARE THE CHARGE OF THE PHOSPHORUS ION TO THE
CHARGE OF THE PHOSPHORUS ATOM.
4. COMPARE THE SIZES.

2. Valence Electrons
Valence Electrons
are the electrons in
the last energy level
of an atom
You can tell the
number of valence
electrons from the
group number 2-8-8-1

3. 1
2 3 4 5 6 7
8

4. Lewis Dot Structure (Electron Dot
Structure)
A notation showing the valence electrons surrounding
the atomic symbol.

5. Rule #1. No side can have
more than two dots.
Rule #2. When filling the
sides of the element symbol
each side gets one dot
before doubling up.
Exceptions are hydrogen and
helium.

6. Elements within the same group have
the same electron-dot structure.

7. Try On your own
 In your notebook, try these elements on your own:
a) H
b) P
c) Ca
d) Ar
e) Cl
f) Al

8. Octet Rule
Octet rule says that atoms like to have
full outer shells of only eight electrons.
Atoms will lose or gain valence
electrons to make their outer shells full,
and they do this by bonding with other
atoms.

9. Formation of Positive Ions
Metals form positive ions by losing electrons
Na  Na+ + e-
2-8-1 2-8

10. Formation of the Magnesium Ion
Mg  Mg2+ + 2e-
Note: Dot structures of metal
ions have no dots. Must include
charge

11. Formation of Negative Ions
Nonmetals gain electrons, forming negative ions
Cl + 1e-  Cl -
2-8-7 2-8-8

12. Formation of Sulfide Ion
+ 2e- 
2-
Note: Nonmetal ions are
surrounded by 8 dots.
Make sure to include
charge.

13. What is the Lewis electron dot diagram
for each ion?
Ca2+
O2−

14. Solution
 Having lost its two original valence electrons, the
Lewis electron dot diagram is just Ca2+.
Ca2+
 The O2− ion has gained two electrons in its valence
shell, so its Lewis electron dot diagram is as
follows:

15. SUMMARY
Lewis electron dot diagrams use dots to
represent valence electrons around an atomic
symbol.
Lewis electron dot diagrams for ions have less
(for (+) ions) or more (for (-) ions) dots than
the corresponding atom.

16. PRACTICE QUESTIONS
1. Draw the Lewis electron dot diagram for each
element.
bromine
gallium
2. Draw the Lewis electron dot diagram for each
ion.
Mg+2 Mg+2
S−2