9th Grade Physical Science
Unit 4: Organizing the Elements
Activity #6a: Designing Ionic Compounds
#6a
To Begin
The valence electrons of an atom are involved in bonding
(combining) with other atoms. We will explore how that occurs
both for ionic bonding (by forming + and – ions that are attracted
to each other) and for covalent bonding (sharing of electrons).
Learning Goals
• Students will be able to show valence electrons of any element
using Lewis dot symbols.
• Students will be able to show the transfer of electrons between
the elements that form ionic compounds.
• Students will be able to determine the ratios of + and – ions in any neutral ionic compound.
• Students will be able to use chemical symbols (ie. CaCl2) to identify the number of atoms of each element in
complex chemical compounds.
Process & Procedure
1. Think about the number of valence electrons associated with any stable ion. How does that number relate to the
number of outer electrons found in its nearest noble gas?
2. Read the information below to find out more about this number and to learn about a bookkeeping method used to
keep track of the electrons in an outer shell of an atom. As you read be sure to define terms that are unfamiliar to
you and provide examples.
The Octet Rule and Lewis Dot Diagrams
The concept of electron configurations allowed chemists to explain why chemical molecules are formed from the
elements. Do you know what is meant by electron configuration?
In 1916 the American chemist, Gilbert Lewis, proposed that atoms achieve a noble gas electronic configuration by
gaining, losing or sharing electrons with other atoms. Do you know the electron configuration of Neon? Of Argon?
Since the noble gases (except He) have 8 valence electrons, his proposal is known as the octet rule. A valence
electron is an electron that is in the outer shell of an atom and is involved in bonding with other elements.
The rule states that, except for hydrogen, an atom combines with other atoms to form bonds in order to have 8
electrons in its valence shell. Hydrogen shares electrons with other atoms to achieve the He electronic configuration
of 2. Lewis dot diagrams are representations of the elements which give a dot  for each valence electron on the
atom.
The Lewis dot symbols for the period 2 elements are:
Note: Transition metals (and the lanthanides and actinides) can't be represented by simple Lewis Dot symbols.
3. Valence Electrons. Use the table below to complete the following the Lewis Dot Diagrams for the elements below
(skipping transition metal) (The first one, H, has been done for you as an example):
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Ga
Ge
As
Se
Br
Kr
4. Look for a pattern!!! Summarize your pattern thinking about how valence electrons relate to column, type of ion,
etc.
5. Lewis Dot Structures and Ionic Bonds
Lewis dot structures allow us to visualize how ions combine to form ionic compounds.
a. Ionic bonds are usually formed by the reaction of metals with non-metals. An ionic bond is formed when one
element gives an electron away and the other element accepts the electron.
For example, sodium reacts explosively with
chlorine gas to form sodium chloride:
2 Na (s) + Cl2 (g) → 2 NaCl (s)
Or, we can use Lewis dot structures to visualize the
process as seen in the diagram to the right.
b. Use similar Lewis dot structures to show how calcium metal reacts with oxygen gas to form calcium oxide:
2 Ca (s) + O2 (g)  2 CaO (s)
c. These ions are then held together in a crystal lattice structure by the interaction of their charges (force of
attraction between opposite charges). No chemical bonds are formed between the - ions and the + ions.
The final ionic equation for the formation of NaCl, can be written:
Na1+(aq) + Cl1-(aq)  NaCl (s)
Notice that this is the reverse of a dissociation equation:
d. Write the ionic equation for the formation of CaO.
e. It is common practice to place brackets around ions
that have achieved a noble gas electron
configuration. Positive ions that have lost electrons
use an empty bracket. Negative ions that have
gained electrons to reach 8 electrons show those
electrons in the bracket.
f.
6.
Use brackets with your Lewis dot to show how
calcium metal reacts with oxygen gas to form
calcium oxide.
NaCl (s)  Na1+(aq) + Cl1-(aq)
6. Practice Lewis Dot Structures: Use Lewis dot structures to show the transfer of electrons (example on previous
page) between the following atoms to form stable, neutral ionic compounds:
K and Cl
O and Ba
Na and S
7. Based on valence electrons (look at the electron configuration on your periodic table), complete the table for the
following common ions. The first one is done for you.
Positively Charged Ions
Negatively Charged Ions
Lithium ion
Li1+
Chloride ion
Barium ion
Oxide ion (oxygen)
Aluminum ion
Nitride ion (nitrogen)
8. Use the information above to complete this table. Remember the chemical formula will always result in a
neutral ionic compound!
Name of Compound Chemical Lewis Dot Diagram
Dissociation Equation
Formula
Lithium Chloride
LiCl
LiCl(s)  Li+ (aq) + Cl-(aq)
Lithium Oxide
Lithium Nitride
Li3N
Barium Chloride
BaCl2
Barium Oxide
Barium Nitride
Aluminum Chloride
Aluminum Oxide
Aluminum Nitride
AlN
Stop and Think
The subscript number in a chemical formula refers to how many atoms of that element are present in the compound.
For example, H2O, where the 2 indicates that there are 2 hydrogen atoms in the compound. In this example, oxygen
has no subscript…that means there is only 1 atom of that element in the compound.
1. Complete the table by counting the atoms of each element in the compounds shown.
Chemical
Symbol
# of each type of atom
CaCO3
FeS2
SiO2
Al2O3
2. For more complex compounds, use the distributive properties you learned in math. For example, Fe(SO4)2,
where the subscript 2 multiplies everything in the parentheses before it by 2. The subscript 2 does not multiply
the Fe since it is outside of the parentheses. In this example, there is 1 atom of FE, 2 atoms of S, and 8 atoms
of O.
Complete the table by counting the atoms and using the distributive property as needed.
Chemical
Symbol
# of each type of atom
Ca(H2PO4)2
Ca10(PO4)6(OH)2
(NH4)2HPO4
NH4Fe(SO4)2