Parts of A Chemical Formula and Balancing POGIL
Name
Hour
Standard1 Module 8
Chemical Formulas and Atomic Representations
Background Information and Why? In chemistry we use a language to represent atoms, compounds,
molecules, and chemical changes. Like any language there are certain rules and conventions. One rule pertains
to something called a subscript. This is a small number below and to the right of an atom. This number
represents now many of that atom are connected in a molecule. Another rule is in regards to a coefficient.
This is the large number in front of an atom or molecule. There are also rules for letters. For each atom, alone
or combined in a molecule, there is only one capital letter. This letter also commonly tells us something about
the name of that atom. All of these atoms are arranged on the periodic table of elements. This arrangement is
determined by many physical and chemical properties.
Figure 1
Figure 2
Figure 3
Single Atom one upper
case and no lower case.
Chemical Atomic
Formula
Representation
O
Single Atom one upper case
and one lower case.
Chemical Atomic
Formula
Representation
Ni
N
Au
C
Cl
Multiple atoms one upper case and no
lower case and a subscript meaning the
atoms are chemically bonded or connected.
Chemical
Atomic
Formula
Representation
O2
*the little line represents a
chemical bond that attaches
the atoms.
N3
Figure 4
Multiple atoms one upper case and one
lower case and a subscript meaning the
atoms are chemically bonded or connected.
Chemical
Atomic
Formula
Representation
Zn2
*the little line represents a
chemical bond that attaches
the atoms.
Cl3
Na5
C5
Questions:
1.) How are the examples in figure 1 and figure 2 similar?
2.) How are the examples in figure 1 and 2 different?
3.) How are the examples in figure 3 and figure 4 similar?
4.) How are the examples in figure 3 and figure 4 different?
Figure 5
Chemical
Formula
CO2
(carbon
dioxide)
3 CO2
(carbon
dioxide)
Fe2O3
(rust)
Questions
5.) What is the 2 in CO2 called?
Atomic
Representation
6.) What does the 2 in CO2 mean?
C
O
O
h
*notehwe are going to start using the
s symbol in the atom representation.
chemical
s
sC
O
O
h
h
Cs
O
O
hs
hs
sC
O
O
sh
*noteshthe coefficient 3 means 3 of the CO2
s not connected. These are each a
packages
molecule.
s The subscript 2 means 2 oxygen
atomssare connected inside each molecule.
Fe
Fe
O
O
O
7.) What is the 3 in 3CO2 called?
8.) What does the 3 in 3CO2 mean?
9.) What does the 2 in Fe2O3 mean?
10.) What does the 3 in Fe2O3 mean?
11.) What does the 4 in 4Fe2O3 mean?
12.) You draw the atomic representation for 2HCl in the
space below. The”l” in HCl is a lower case L. Then go
check the key.
Notice the 2 Fe (iron) and the 3 O(oxygen) are
represented by subscripts.
4Fe2O3
(rust)
Fe
Fe
O
O
O
Fe
Fe
O
O
O
Fe
Fe
O
O
O
Fe
Fe
O
O
O
13.) Draw 3Al2O3 in the space below (Hint: the “l” in Al is
a lower case “L”). Then go check the key.
10.)Fill in the following table using what you learned so far.
Chemical Formula
H
2Ni
*there is no
subscript so be
careful.
H2O
3O2
2FeCl2
3H2SO4
2Na2CO4
Atomic Representative (go check the key to check your progress)
Balancing Chemical Equations
Background Information and Why: Chemical reactions can be described by chemical equations. Equations
means equal. One each side of the equal side, also known as “yields”, the number AND type of atoms are
exactly the same. The Law of Conservation of Mass states that the atoms cannot be created or destroyed. The
atoms can only be rearranged into different molecules/substances. Therefore, in order to obey The Law of
Conservation of Mass, the number of atoms for each element must be the same in the reactants (left side) as
it is in the products (right side). In order to balance equations we cannot split or add to existing molecules. We
can change the coefficient, adding molecules. We cannot change the subscripts, the small numbers, because
they determine how many atoms are in a molecule.
Reaction (A)
REACTANTS
PRODUCTS
CuO
Chemical Equation
Atomic Representation
Reaction (B)
Cu
+
O
+
H2
H
Cu +
H
+
H
H
O
REACTANTS
CO
+
Cu
H2O
PRODUCTS
O2
CO2
O
Atomic Representation
C
O
+
C
O
O
O
Questions
11.) How many of each type of atom are represented in each side of reaction A? Count them up and fill out the table
below.
# Atoms in Reactants
Atoms in Products
CuCuO-
O-
H-
H-
12.) Does equation (A) obey the Law of Conservation of Mass? Explain.
13.) How many of each type of atom are represented in each side of reaction B? Count them up and fill out the table
below.
# Atoms in Reactants
Atoms in Products
CCO-
O-
14.) Does equation (B) obey the Law of Conservation of Mass? Explain.
15.) If either reaction/equation A or B does not obey the Law of Conservation of Mass, draw additional molecules on
the reactant and/or product side(s) in order to make the number of all atoms equal on both sides of the equation. HINT:
recall you cannot split existing molecules or add atoms to existing molecules. In other words EXISTING MOLECULES
MUST REMAIN INTACT AND YOU CAN ONLY USE REPLICAS OF WHAT YOU STARTED WITH.???????????????
16.) In reaction (A) how many H2O molecules are produced for every H2 molecule that is needed in the reactants?
17.) In reaction (B) how many CO2 molecules are produced for every O2 molecule that is needed in the reactants?
18.) In reaction (B) how many CO molecules react with every O2 molecule?
19.) In order to answer question 15 you should see that reaction (a) is already drawn correctly, but reaction B does not
have the same number of oxygen atoms on each side. It should be drawn like this….. GO BACK AND CHECK YOURS.
REACTANTS
PRODUCTS
O
C
+
O
C
O
O
O
O
C
C
O
We needed to
add this carbon
dioxide because
we already had
carbon dioxide
O
We needed to
add this carbon monoxide because
we already had carbon monoxide
20.) Recall we can only change the coefficients in a chemical equation. Below are the blanks where coefficients can go.
Look at the new atomic representation for Reaction (B) above and write the correct coefficient in the correct blank.
Yes, can
change these
REACTANTS
2 CO
+
O2
PRODUCTS
2 CO2
NO, CANNOT
change these
21.) This drawing and equation now show how many oxygens in the reactants? How many oxygens in the products?
22.) This drawing and equation now show how many carbons in the reactants? How many carbons in the products?
23.) Is this equation balanced? Explain?