This document discusses different types of chemical formulas used to represent compounds: - A chemical compound is made of two or more elements that are combined in fixed ratios. - The chemical formula uses symbols of the elements and subscripts to show the relative proportions. - The empirical formula shows the lowest whole number ratio of atoms in a compound, while the molecular formula gives the exact number of each atom. - The structural formula depicts the specific bonding arrangement of the atoms in a compound.

1. Chemical
Compounds
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2. CHEMICAL COMPOUND
A compound, when we are talking about
chemistry,
is simply any substance that is made up of two or
more elements which react with one another.
The
elements must be present in fixed ratios.
-: Example :-
Hydrogen and Oxygen are pure elements and are
gases.© iTutor. 2000-2013. All Rights Reserved

3. CHEMICAL FORMULA
A compound is represented by giving its chemical
formula, a notation that uses atomic symbols
with numerical subscripts to convey the relative
proportion of atoms of different elements in the
substance.
H2O
The two elements present
two H atoms per formula unit
Lack of subscript means one atom of O per formula unit
E.g.
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4. TYPES OF CHEMICAL FORMULA
Empirical Formula
Molecular Formula
Structural Formula
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5. EMPIRICAL FORMULA
 The empirical formula indicates the different
types of elements in a molecule and the lowest
whole-number ratio of each kind of atom in the
molecule.
 Compounds with different molecular formulas
can have the same empirical formulas and such
substances will have the same percentage
composition.
Acetic acid (C2H4O2), formaldehyde (CH2O), and
glucose
(C6H12O6) all have the empirical formula CH2O.© iTutor. 2000-2013. All Rights Reserved

6. STEPS TO CALCULATE EMPIRICAL FORMULA
 Step 1: assume the mass to be 100g so the
percent becomes grams
 Step 2: determine the moles of each element
 Step 3: determine the mole ratio by dividing
each elements number of moles by the
smallest
 Step 4: Double, triple .. to get an integer is
they are not all whole numbers
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7. EXAMPLE
What is the empirical formula given percent
composition?
62.1% of C, 5.21% of H, 12.1% of N, and 20.7% of O
Solution
Step 1 : Mass is 100% so % becomes grams
62.1g C, 5.21gH, 12.1g N, and 20.7g O
Step 2 : determine the moles of each element
62.1 g C x (12.0 g C / mole) = 5.18 moles C
5.21 g H x (1.0 g H / mole) = 5.21 moles H
12.1 g N x (14.0 g N / mole) = 0.864 moles N
20.7 g O x (16.0 g O / mole) = 1.29 moles O
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8. EXAMPLE
Step 3 : determine the mole ratio by dividing each
elements number of moles by the smallest
Dividing by the smallest (0.864) we get
C: 5.18 / 0.864 = 6.00
H: 5.21 / 0.864 = 6.03
N: 0.864 / 0.864 = 1.00
O: 1.29 / 0.864 = 1.49
Step 4 : Double, triple .. to get an integer is they are
not
all whole numbers
To get all integers, double these values and you get
C12H12N2O3
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9. MOLECULAR FORMULA
 A molecular formula is based on an actual
molecule of a compound. It gives the exact number
of different atoms of an element in a molecule. In
some cases, the empirical formula and the
molecular formula are identical
 E.g. formaldehyde CH2O. In other cases, the
molecular formula is a multiple of the empirical
formula unit E.g. C6H12O6 = (CH2O)6
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10. STEPS TO CALCULATE MOLECULAR FORMULA
 Step 1 After you determine the empirical
formula, determine its mass.
 Step 2 Determine how many times greater
the molecular mass is compared to the mass
of the empirical formula.
 Step 3 Multiply the empirical formula by this
number
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11. EXAMPLE
From the percentages you get an empirical formula of
CH2 and the molecular mass is 56.0g/mol.
Solution
Step 1 : After you determine the empirical formula,
determine its mass.
CH2
1 carbon 12.0 + 2 (hydrogen's 1.0) =14.0g/mol
Step 2 : Determine how many times greater the molecular
mass is compared to the mass of the empirical formula.
molecular mass/ empirical formulas mass
56.0g/mol / 14.0g/mol = 4
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12. EXAMPLE
Step 3 : Multiply the empirical formula by this number
4x CH2 =C4H8
Note: Some compounds have the same empirical and
molecular formula.
For example : Carbon Dioxide has as its empirical
and molecular formula CO2.
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13. STRUCTURAL FORMULA
The structural formula shows the elements in
the
compound, the exact number of each atom in
the
compound, and the bonding pattern for the
compound. The electron-dot formula and Lewis
formula are examples of structural formulas.
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14. STRUCTURAL FORMULA
Both compounds in the figure have two carbon
atoms, six hydrogen atoms, and one oxygen
atom. The difference is in the way the atoms
are
bonded© iTutor. 2000-2013. All Rights Reserved

15. THE END
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