Chapter 7 Naming, Empirical Formula, Molecular Formula and Percent Composition.
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Transcript of Chapter 7 Naming, Empirical Formula, Molecular Formula and Percent Composition.
7.1 Chemical Names and Formulas
C8H18
8 Carbon atoms 18 Hydrogen Atoms
Al2(SO4)3
2 Aluminum atoms 4 Oxygen atoms 3 of everything in ( ) making 3 Sulfur atoms and 12 Oxygen atoms total
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Monatomic Ions:: ions formed from a single atom ::
NAMING :: Element Root + -ide
F F-
Flourine Flouride anion N N3-
Nitrogen Nitride anion
O2- = ?
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Binary Ionic CompoundsNomenclature :: naming system
Naming ::
Al2O3
Name of Cation Name of Anion
(with –ide ending)
Aluminum Oxide
Writing the Formula
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Nomenclature :: The Stock System
Some elements [such as transition metals] form two or more cations with different charges. The stock system is used to distinguish between the different ions of an element.
Fe2+ Iron (II) Fe3+ Iron (III)
CuCl2 Cu2+ Cl- Name of Cation + Roman Numeral Name of Anion
indicating charge
Copper (II) Chloride
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Polyatomic Ions & Oxyanionsoxyanions :: polyatomic ions that contain oxygen
1 less O than ___ite has 1 less O than other oxyanion has 1 more O than other oxyanion 1 more O than ___ate
ClO- ClO2 ClO3 ClO4
Hypochlorite Chlorite Chlorate Perchlorate
Common Polyatomic Ions:
NO3- SO4
2- CO32- PO4
3- OH- NH4+
Nitrate Sulfate Carbonate Phosphate Hydroxide Ammonium
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Binary Molecular Compounds
NAMING RULES1. First element does not take a
prefix if it only contributes 1 atom to the compound
2. Second element takes prefix, drop ending, add –ide
3. The o or a at the end of prefix is dropped if the element begins with a vowel
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P4O10
Prefix [if needed] + Prefix [determined by # Name of element
atoms] + root name + -ide
Tetraphosphorus decoxide
PREFIXES
# atoms Prefix # atoms Prefix
1 mono- 6 hexa-
2 di- 7 hepta-
3 tri- 8 octa-
4 tetra- 9 nona-
5 penta- 10 deca-
Naming Acids Have O ?
Yes No Poly atomic ion root + suffix Acid Hydro________ic Acid [Hydro + root + ic Acid]
HNO3 Nitric Acid Ex: HCl Hydrochloric acid
Nitrate Nitric Acid HF Hydrofluoric acid HNO2 Nitrous Acid
HClO4 Perchloric Acid
HClO2 Hypochlorous Acid
HClO3 Chloric Acid
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ACID SUFFIXES
Polyatomic Ion suffix Acid suffix
- ate [nitrate] -ic [nitric]
-ite [nitrite] -ous [nitrous]
7.2 Oxidation Numbers
Oxidation number :: numbers assigned to compound or ion to indicate the general distribution of electrons among the bonded atoms in a molecular compound/ion
Oxidation numbers are helpful in naming compounds, writing formulas, and balancing chemical equations [redox!!]
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Rules for Assigning Oxidation Numbers
1. Atoms in pure element have oxidation number zero (0).2. Elements in a binary molecular compound are given oxidations numbers equal to
the charges they would have as ions3. Flourine always has an oxidation number of -1.4. Oxygen has an oxidation number of -2 in every compound except for peroxides (like
H2O2), where it is -1, and with halogens, has oxidation number +2 (OF2)
5. Hydrogen has oxidation number +1 in compounds with elements more electronegative than itself; it has oxidation number -1 in metal compounds
6. Algebraic sum of oxidation numbers of all atoms in compound add up to charge of compound
7. Monatomic ions have oxidation numbers equal to their charges.8. Rules 1-7 apply to covalently bonded atoms, but oxidation numbers can also be
assigned to atoms in ionic compounds.
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Assigning Oxidation Numbers
UF6 We know that fluorine has oxidation # -1. There are 6 F atoms, so -1 x 6 = -6.
Also, the sum of oxidation numbers must equal the charge of the compound, or O, in this case. U + (-6) = 0. Therefore, the Oxidation number of U = +6.
Oxidation Number: U: +6 F: -1
ClO3- Oxygen has oxidation # of -2. Total of oxidation numbers must add up to -1.
Therefore, Cl has oxidation number of +5. Oxidation Number: Cl: +5 O: -2
Oxidation number S in H2SO4 ?? Answer: +6
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
7.3 Using Chemical Formulas
Chemical Names & Formulas Oxidation Numbers Using Chemical FormulasDetermining Chemical Formulas Questions
Formula Mass :: sum of the average atomic masses of all the atoms represented in its formula
FOR EXAMPLE :The formula mass for H2O is:
Average atomic mass for H : 1.01 amuAverage atomic mass of O : 16.00 amu
2 H atoms x 1.01 amu = 2.02 amu1 O atom x 16.00 amu = 16.00 amu
formula mass of H2O = 18.02 amu
© 2009, Prentice-Hall, Inc.
Formula Weight (FW)• A formula weight is the sum of the atomic
weights for the atoms in a chemical formula.
• So, the formula weight of calcium chloride, CaCl2, would be
Ca: 1(40.1 amu) + Cl: 2(35.5 amu)
111.1 amu
• Formula weights are generally reported for ionic compounds.
© 2009, Prentice-Hall, Inc.
Molecular Weight (MW)
• A molecular weight is the sum of the atomic weights of the atoms in a molecule.
• For the molecule ethane, C2H6, the molecular weight would be
C: 2(12.0 amu)
30.0 amu+ H: 6(1.0 amu)
© 2009, Prentice-Hall, Inc.
Percent Composition
One can find the percentage of the mass of a compound that comes from each of the elements in the compound by using this equation:
% element =(number of atoms)(atomic weight)
(FW of the compound)x 100
© 2009, Prentice-Hall, Inc.
Percent Composition
So the percentage of carbon in ethane is…
%C =(2)(12.0 amu)
(30.0 amu)
24.0 amu
30.0 amu= x 100
= 80.0%
© 2009, Prentice-Hall, Inc.
Chemical FormulasThe subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound.
© 2009, Prentice-Hall, Inc.
Types of Formulas
• Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound.
• Molecular formulas give the exact number of atoms of each element in a compound.
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
One can calculate the empirical formula from the percent composition.
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
The compound para-aminobenzoic acid (you may have seen it listed as PABA on your bottle of sunscreen) is composed of carbon (61.31%), hydrogen (5.14%), nitrogen (10.21%), and oxygen (23.33%). Find the empirical formula of PABA.
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
Assuming 100.00 g of para-aminobenzoic acid,
C: 61.31 g x = 5.105 mol C
H: 5.14 g x = 5.09 mol H
N: 10.21 g x = 0.7288 mol N
O: 23.33 g x = 1.456 mol O
1 mol12.01 g
1 mol14.01 g
1 mol1.01 g
1 mol16.00 g
© 2009, Prentice-Hall, Inc.
Calculating Empirical FormulasCalculate the mole ratio by dividing by the smallest number of moles:
C: = 7.005 7
H: = 6.984 7
N: = 1.000
O: = 2.001 2
5.105 mol0.7288 mol
5.09 mol0.7288 mol
0.7288 mol0.7288 mol
1.458 mol0.7288 mol
© 2009, Prentice-Hall, Inc.
Calculating Empirical Formulas
These are the subscripts for the empirical formula:
C7H7NO2
Molecular FormulaActual ratio of atoms in a compound. Ex. H2O, C6H12O6
To determine the molecular formula, divide the molar mass by empirical formula mass. This will give the number of empirical formula units (n) in actual molecule.
n= Molar Mass/ Empirical Formula Mass
Ex. Determine the empirical and molecular formula of each of the following: 1.Ethylene glycol, the substance used as antifreeze has 38.70 % C, 9.70 % H and 51.60 % O , mm= 62.10 g2.Caffeine, a stimulant in coffee has the following percent composition:49.50 % C, 5.15% H, 28.90 % N and 16.50 % O , molar mass= 195.00g