Formulas & Names, Empirical and Molecular Formulas
A compound is a substance composed of two or more different elements that are chemically
combined in a fixed proportion. A chemical compound can only be broken down by chemical
means.
1. Chemical compounds can be represented by a specific formula and assigned a name based
on the IUPAC system.
2. Ionic compounds naming rules
 name the metal and then the nonmetal but end the nonmetal with-ide if it is a binary
compound Ex NaCl sodium chloride
 If the metal is not from Group I ,II or Ag, Cd, Zn, Ga or Al then the name of the metal is
followed by a roman numeral that states the oxidation number of the metal ex. FeCl3 is iron
(III) chloride
 If the ionic compound consists of a metal and polyatomic: name the metal followed by the
polyatomic Ex. Mg SO4 magnesium sulfate
3. Molecular/Covalent Compounds naming rules
 Name the element furthest to the left first then followed by the one to the right. Prefixes are used
in naming the first element only when greater than the one. Prefixes are always used when naming
the second element Ex N2O2 dinitrogen dioxide
4. Acid Naming rules
 Binary acids start with Hydro and end with the non-metal with an –ic ending Ex.HCl
hydrochloric acid
 Ternary acids(so acids with a polyatomic) don’t have hydro in the name and all you do is
change the polyatomic ending -ate goes to –ic and -ite goes to –ous
 Ex HClO3 chloric acid
6. Types of chemical formulas include empirical, molecular, and structural.
 Empirical formulas show elements in their simplest whole number ratios. This may or may not be
the same as the molecular formula.
 To find the empirical formula follow the following limerick
% to grams, grams to moles, divide by small (the smallest mole present) multiply to whole (if
necessary).
Ex. Find the empirical formula of the following compound.
40% C, 6.72% H and 53.2% O
%>grams
grams>moles
1𝑚𝑜𝑙𝑒 𝐶
40% =40 g.C x
=3.331 moles C
12𝑔𝑟𝑎𝑚𝑠
1𝑚𝑜𝑙𝑒 𝐻
6.72% H= 6.72 g H x
1.01 𝑔
1𝑚𝑜𝑙𝑒 𝑂
=6.67 moles H
divide by small
Formula
3.331 𝑚𝑜𝑙𝑒𝑠𝐶 ⁄3.331 𝑚𝑜𝑙𝑒𝑠 =1
6.67 𝑚𝑜𝑙𝑒𝑠𝐻 ⁄3.31 𝑚𝑜𝑙𝑒𝑠 =2
CH2O
53.2% O = 53.2g O x 16.00 𝑔 =3.331 moles O 3.31𝑚𝑜𝑙𝑒𝑠𝑂⁄3.31𝑚𝑜𝑙𝑒𝑠 =1
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Molecular formulas show the actual number of atoms per element in a single molecule.
Ex. Given the molecular formula mass of 180 grams what is the molecular formula given the
empirical formula CH2O
The molecular formula is always a multiple of the empirical formula so if the empirical formula is
CH2O then the empirical formula mass would be 30grams
𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝐹𝑜𝑟𝑚𝑢𝑙𝑎 𝑀𝑎𝑠𝑠⁄𝐸𝑚𝑝𝑖𝑟𝑖𝑐𝑎𝑙 𝐹𝑜𝑟𝑚𝑢𝑙𝑎 𝑀𝑎𝑠𝑠= multiplier or
180 𝑔⁄30 𝑔= 6 or 6(CH2O) molecular formula = C6H12O6
Structural formulas show the number of each type of atom as well as their physical arrangement.
Practice Problems
1. What is the empirical formula of C3H6?
A. CH
B. CH2
C. CH3
D. CH6
2. The name of the compound KClO2 is potassium
A. hypochlorite
B. chlorate
C. chlorite
D. perchlorate
3. Which formula is correct for ammonium sulfate?
A.
B.
C.
D.
NH4SO4
(NH4)2SO4
NH4(SO4)2
(NH)3(SO4)2
4. The molecular formula of a compound is represented by X3Y6. What is the empirical
formula of this compound?
A. X3Y
B. X2Y
C. XY2
D. XY
5. Consider a mystery compound having the formula MxTy. If the compound is not an
acid, if it contains only two elements, and if M is not a metal, which of the following is
true about the compound?
A. It contains a polyatomic ion
B. It is a binary molecular compound
C. Its name ends in –ic
D. It is a binary ionic compound
E. Its name ends in –ite or –ate
6. Which of the following is a binary molecular compound?
A. BeHCO3
B. AgI
C. MgS
D. PCl5
E. Cr2O3
7. What is the oxidation number of a fluoride ion?
A. -1
B. +1
C. -2
D. +2
8. What is the molecular formula of a compound with a molar mass of 92.011 g/mol and
an empirical formula of NO2?
A. NO5
B. N2O4
C. N3O3
D. N3O6
9. What is the name of the compound PbO2 according to IUPAC rules?
The chemical name is
A. Dilead oxide
B. Tetralead dioxygen
C. Lead (II) oxide
D. Lead (IV) oxide
10. Which of these represents the empirical formula and the molecular formula, respectively,
for a given organic compound?
A. CH and C2H2
B. CH and CH4
C. CH2 and C2H2
D. CH3 and C3H12
11. A compound has 50% sulfur and 50% oxygen. What is its empirical formula?
A. SO4
B. S2O4
C. SO3
D. SO2
12. A compound is composed of 85.64% carbon and 14.36% hydrogen. The compound has a
formula mass of 42.08 grams. What is the molecular formula?
A. CH
B. C3H6
C. C2H4
D. C2H18
A. _
Answers 1A, 2C,3B, 4D, 5B, 6D, 7A , 8B, 9D, 10A, 11D, 12B