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Lecture 4

CHEM 131 Lecture Notes - Lecture 4: Ionic Compound, Nitride, Formula Unit


Department
Chemistry
Course Code
CHEM 131
Professor
Shuhua Ma
Lecture
4

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Chem 131 9/8
Chemical Formulas
Formulas that express the composition of molecules and ionic
compounds in terms of chemical symbols
Molecular Formula
Shows the exact number of atoms of each element in the smallest unit of
a substance
o Example: C6H1206
Empirical Formula
Shows the simplest whole-number ratio of the atoms in a substance
o Example: CH2O6 (simplest whole-number ratio of C6H12O6)
Allotrope
One of two or more distinct forms of an element
Examples of writing Molecular vs. Empirical Formulas:
Example 1:
o Molecular:
CH2O3
H2CO3 (Better to recognize)
o Empirical:
CH2O3
H2CO3 (Better to recognize)
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2
Example 2:
o Molecular:
H2O2
o Empirical:
HO
Example 3:
o Molecular:
C2H6
o Empirical:
CH3
Example 4:
o Molecular:
C6H6
o Empirical:
CH
Ionic Compounds
Consists of a combination of cations and anions
o The formula is usually the same as the empirical formula
o The sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
Example:
o The ionic compound Na+Cl-
o The positive on Na and the negative on Cl cancel each other out,
making the sum of the charges on the cation(s) and anion(s)
equal to zero
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