Naming, Empirical Formula, Molecular Formula and Percent Composition Chapter 7 Naming, Empirical Formula, Molecular Formula and Percent Composition

7.1 Chemical Names and Formulas 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 Formulas Determining Chemical Formulas Questions

Monatomic Ions NAMING :: Element Root + -ide O2- = ? :: 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 Formulas Determining Chemical Formulas Questions

Binary Ionic Compounds Nomenclature :: 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 Formulas Determining Chemical Formulas Questions

Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining 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 Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

Polyatomic Ions & Oxyanions oxyanions :: 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- SO42- CO32- PO43- OH- NH4+ Nitrate Sulfate Carbonate Phosphate Hydroxide Ammonium Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

Binary Molecular Compounds NAMING RULES 1. 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 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- P4O10 Prefix [if needed] + Prefix [determined by # Name of element atoms] + root name + -ide Tetraphosphorus decoxide Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

Naming Acids Have O ? ACID SUFFIXES Chemical Names & Formulas 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 ACID SUFFIXES Polyatomic Ion suffix Acid suffix - ate [nitrate]  -ic [nitric] -ite [nitrite]  -ous [nitrous] Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

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 Formulas Determining Chemical Formulas Questions

Rules for Assigning Oxidation Numbers Atoms in pure element have oxidation number zero (0). Elements in a binary molecular compound are given oxidations numbers equal to the charges they would have as ions Flourine always has an oxidation number of -1. 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) Hydrogen has oxidation number +1 in compounds with elements more electronegative than itself; it has oxidation number -1 in metal compounds Algebraic sum of oxidation numbers of all atoms in compound add up to charge of compound Monatomic ions have oxidation numbers equal to their charges. 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 Formulas Determining 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 Formulas Determining Chemical Formulas Questions

7.3 Using Chemical Formulas 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 amu Average atomic mass of O : 16.00 amu 2 H atoms x 1.01 amu = 2.02 amu 1 O atom x 16.00 amu = 16.00 amu formula mass of H2O = 18.02 amu  Chemical Names & Formulas Oxidation Numbers Using Chemical Formulas Determining Chemical Formulas Questions

Formula Weights © 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) + H: 6(1.0 amu) 30.0 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… (2)(12.0 amu) (30.0 amu) 24.0 amu 30.0 amu = x 100 = 80.0% © 2009, Prentice-Hall, Inc.

Chemical Formulas The 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.

Finding Empirical Formulas © 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 mol 12.01 g 14.01 g 1.01 g 16.00 g © 2009, Prentice-Hall, Inc.

Calculating Empirical Formulas Calculate 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 mol 0.7288 mol 5.09 mol 1.458 mol © 2009, Prentice-Hall, Inc.

Calculating Empirical Formulas These are the subscripts for the empirical formula: C7H7NO2 © 2009, Prentice-Hall, Inc.

Molecular Formula Actual 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: Ethylene glycol, the substance used as antifreeze has 38.70 % C, 9.70 % H and 51.60 % O , mm= 62.10 g 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