Topic 7: Chemical Formulas and Equations
Key concept
Definitions and facts
Key examples
H2 NaCl C6H12O6
expression of qualitative and
quantitative composition of
are chemical formulas
elements and compounds (pure
substances)
1. Chemical
formula
2. Qualitative What elements are in a formula
in H2O there are
H and O atoms
3. Quantitative Number of each element in the
formula
in H2O there are
2 H atoms and
1 O atom
a whole number that indicates
how many elements in a formula
4. Subscript
H2 O
subscripts
5. Counting
atoms
Simple formula
H2SO4
2H 1S 4O
7 Total atoms
Formula w/parenthesis (NH4)2O
2N 8H 1O
11 Total atoms
Formula of hydrate CuSO4.5H2O 1Cu 1S 10H 9O
21 Total atoms
6. Counting
Ions
(ratio of ions)
(
Binary ionic formula
CaCl2
1Ca2+
:
2Cl-
calcium chloride
ion
ion
Polyatomic ion formula Al2(SO4)3 2 Al3+ : 3SO42aluminum sulfate
(with parenthesis)
ion
Polyatomic ion formula
(without parenthesis)
1K+
KNO3
ion
: 1NO3
potassium
ion
.
nitrate
ion
1
Topic 7: Chemical Formulas and Equations
Key Concept
7. Molecular
formula
8. Empirical
formula
9. Structural
formula
Definitions and facts
Examples
shows true composition H2O CO C2H6 are
of a known substance
molecular formulas for
known substances (water,
carbon monoxide, ethane)
H2O and CO are also
shows elements in
simplest whole- number formulas in the empirical
form because the ratio of
ratio
atoms (2 :1 in H2O and 1:1
in CO) are in the simplest
ratio.
shows how atoms of a
substance are bonded
together
H2O
O
H
H
H H
C2H6
H–C–C–H
H H
10. Reducing
formula to
empirical
formula
given formulas
NO2 K2S2O4 C3H6
. Find Greatest
Common Factor (GCF)
GCF
for all subscripts in
the given formula
. Divide each subscript
by GCF to get
empirical formula
2
1
2
NO2
KSO2
3
CH2
empirical formulas
Topic 7: Chemical Formulas and Equations
Key Concept
11. Writing
Correct
Chemical
formulas
Explanation
A correct chemical
formula must be
electrically neutral
Examples
. Sum of charges in the
formula must equal 0
In all the correct formulas
below, the sum of
+ and – charges in the
formula is equal to 0
.correct subscripts of a
formula allow total
charges in a formula to
equal 0
Below, names of
substances are given.
The correct formula to each
substance is given.
potassium chloride
12. A correct
formula
must
have:
. correct atom symbols
for substance it represents
correct
wrong
KCl
PCl
magnesium nitrate
correct
wrong
Mg(NO3)2
Mg3N2
and
. correct number
(subscript) of each
atom for the substance
Calcium fluoride
correct
CaF2
wrong
CaF
.
Iron (III) oxide
correct
Fe2O3
.
wrong
Fe3O2
3
Topic 7: Chemical Formulas and Equations
Types of compound
13. Binary compound
(names end with –ide)
How to write formula
Examples
. Get symbols of
magnesium fluoride
atoms and charges
Mg2+ F from Periodic Table
Criss-cross charge
Mg F2
values so each
becomes subscript for
the other element
MgF2
Remove subscript of 1
If subscripts after
criss-crossing are
reducible, reduce
them by common
factor to empirical
Barium oxide
Ba2+ O
Ba 2 O 2
BaO
. Get symbols from
14. Polyatomic ion
Sodium sulf
compounds (names Table E and Periodic
end with –ate or –ite) Table
. ALWAYS PUT
Na1+ (SO4)
parenthesis around
(polyatomic atoms)
. Criss-cross charge values
. Remove parenthesis
if subscript outside
the parenthesis is a 1
. Keep parenthesis if
subscript outside is
or more
15. Compounds with
Roman Numeral
Use Roman numeral
value as + charge of the
first element
Na (SO4)1
Na2 SO4
ammonium sulfide
+1
(NH4) S
(NH4) S1
(NH4) S
Titanium (III) ox
Ti
O
Ti2 O
Iron ( ) sulf
Fe
(SO3)
FeSO3
4
Topic 7: Chemical Formulas and Equations
Types of formulas
16. Naming
chemical
formulas
(Ionics)
How to name
Examples
a correct chemical name Below, formulas of
must have:
substances are given.
The correct name to each
substance is given.
Na I
correct
. Correct names of
atoms or ions given in sodium
the formula
iodide
wrong
sodium
iodate
K2SO4
correct
. correct name ending is
potassium
used
sulfate
wrong
potassium
sulfide
MnO
. Roman numeral (if
necessary) is used
correctly
Naming:
17. Binary formulas
(Ionics)
To name binary formulas:
.Get names of atoms
from Periodic Table
- Keep name of 1st atom
correct
wrong
manganese
(II)
oxide
manganese
(I)
oxide
ZnBr2
zinc
bromine
zinc
brom
- Change nonmetal (2nd)
SrO
atom name ending to
strontium oxygen
-ide
Strontium
.
ox
5
Topic 7: Chemical Formulas and Equations
Types of formulas
18. Formulas with
polyatomic ions
(Table E)
How to name
. Get name of element
from Periodic Table
Get name of polyatomic
ion from Table E
.Keep both names as is
(no change to names)
. Change nonmetal ending
to –ide
.Write names of element
19. Formulas with
and/or polyatomic ions
multiple oxidation . Put parenthesis between
number atom
them.
(Using Roman
.
Use
of second
numeral)
symbol as Roman
numeral value in ( )
Examples
Na ClO3
sodium chlorate
NH4Cl
N2O
Nitrogen (I ) oxide
Sn (NO3)4
Tin ( ) nitrate
Tin (
) nitrate
Sometimes, you need to
use math to determine
Cr N2
correct Roman numeral:
. Assign – charge to
second atom (Use Tables)
3Cr N2
. Determine total – by
multiplying the – charge
-6
by the subscript
Use (in parenthesis) total
+6
+ charge value needed to
add to total – to equal 0. Chromium (VI) nitride
20. Naming using prefixes
(prefixes indicate number of atom)
1 (mono)
6 (hexa)
2 (di)
7 (hepta)
3 (tri)
8 (octa)
4 (tetra)
9 (non)
5 (penta)
10 (deca)
Used for covalent compounds only!
6
CO
(carbon
PCl
(phosphorous
oxide)
N O (
nitrogen
H S (
hydrogen
chloride)
oxide)
sulfide)
NOTE: mono can’t be used to start
naming when there is just one of the
first element
Topic 7: Chemical Formulas and Equations
Key Concept
Definitions and facts
21. Equation
shows changes that are
taking place in substances
22. Physical
equation
shows changes that do
not change compositions
of substances (physical
change)
23. Chemical
equation
Shows changes in
compositions of one or
more substances
(chemical changes)
24. Nuclear
equation
Shows changes of
nucleus contents of one
or more atoms (nuclear
change or transmutation)
25. Chemical
reactions
ways by which chemical
changes occur
26. Reactants
Starting substances that
will be changed in
chemical reaction
27. Products
Substances remaining
after a change had
occurred in reaction
Examples
H2O(l) ---- > H2O(s)
H2(g) + O2(g) ---> H2 O(l)
220 Fr
---- > 4He + 216At
28. Coefficients whole-numbers in front
of substances in
equations.
Indicate number of
moles (how many) of the
substance
29. Arrow
Separates Reactants from
Products, and can read as
“yields” or “produces”
7
Topic 7: Chemical Formulas and Equations
Types of reactions
30. Synthesis
(combination)
Explanations
Two or more
reactants combined
to make one product
Examples
+
2H2 + O2 -- > 2H2O
31.Decomposition One reactant breaks
to make two or more
(Analysis)
products
+
2H2O ----> 2H2 + O2
32. Single
Replacement
33. Double
Replacement
34. Combustion
(oxidation)
35. Law of
Conservation
One (a more
reactive) reactant
replaces a less
reactive element of a
compound
+
+
Zn + 2HCl --->ZnCl2 +H2
Ions from
compound reactants
+
+
switche with each
other to form
NaCl + AgNO3 ---->NaNO3 + AgCl
different compounds
a carbon compound
burns in the present
of oxygen
CH4 + O2 --- > CO2 + H2O
)
During
chemical reactions: neither atoms, mass,
charge or energy is created nor destroyed.
The total number of atoms, charge, and energy are
the same before and after a reaction (conserved)
36. A balanced
chemical
equation
An equation that shows conservation
N2 + H2 ---- > NH3
allows
2N
2N
this equation to be
6H
6H
balanced.
atoms of
atoms of
=
reactants
8
products
Topic 7: Chemical Formulas and Equations
Key concept
36.
36.Law of conservation
of mass
Example
During a chemical reaction, mass of
substances before and after the reaction is
the same.
3Fe
20.9 g
+
2O2 ------- > Fe3O4 :
8.0 g
=
28.9 g
NOTE: The total mass of Fe and O2
(reactants) is the same as the total mass of
Fe3O4 (product)
37. Balancing equation
37.
An equation
Balancing
is balanced
equationwhen
usingit acontains the correct combination of
smallest
RAPwhole-number
table.
coefficients. The coefficients allow number of each
atomThe
on both
use ofsides
a Table
of the
is optional
equation to be the same.
To balance an equation:
One or more coefficients in front of the substances must be changed in the
equation.
The right combination of coefficients will make the number of atoms on
both sides equal.
Suggestion to balancing equations
. Make a table (optional) to keep track of number of atoms as coefficients
are changed
. Try balancing one atom at a time
. Every time a coefficient is changed, RECOUNT the number of each
atom affected by the change. NOTE changes on the table. (be sure to
count atoms correctly)
. Always change coefficients of free elements (Na, Cl2) last
. Always put parenthesis around polyatomic ions and count it as one unit
. Be sure that coefficients are in smallest whole-number ratio
38. Sums of all coefficient: After you had balance an equation, you
may be asked for the sum of all coefficients.
(which may not be written in front of the substances)
Examples of balanced equations and sums of coefficients are given on the
next page.
.
9
Topic 7: Chemical Formulas and Equations
39. Balanced equations and sum of coefficients
Li3N
Unbalanced
------> Li
+ N2
Balanced
2Li3N -------> 6 Li
+ N2
Sum of all coefficients
2
+ 1
3Ca(OH)2 + 2H3PO4 ---- > Ca3(PO4)2 + 6H2O
Sum of coefficients 3
Unbalanced
+ 2
C3H4 +
+
O2
Balanced
C3H4 + 4O2
Sum of coefficients
1
10
= 9
Ca(OH)2 + H3PO4 ----- > Ca3(PO4)2 + H2O
Unbalanced
Balanced
+ 6
+ 4
1
----- > CO2
+ 6=
+
------ > 3CO2 +
+
3
+
12
H2O
2H2O
2 = 9