Modern Chemistry Chapter 7 Chemical Formulas and Chemical Compounds

Chemical Names and Formulas Section 1 Chemical Names and Formulas

Chemical Formula C H Molecular compounds – for one molecule Ionic compounds – for one formula unit; the simplest ratio of cations to anions C H 8 18 Eighteen hydrogen atoms in the molecule Eight carbon atoms in the molecule

Chemical Formula Al (SO ) 5 ions – two Al 3+ ions and three (SO4) 2- ions Al (SO ) 2 4 3 4 SO4 ions 2 Al atoms 4 O atoms

Definitions Binary Compound – compound with only two types of atoms Nomenclature – a naming system Salt- an ionic compound composed of a cation and an anion from an acid

Definitions Monatomic ions – ions formed from a single atom For negative monatomic ions, -ide is added to the root name

How can I tell if the compound is ionic or covalent ???? Ionic compounds contain a metal and a nonmetal or a polyatomic ion !!!

Writing Fomulas and Naming Ionic Compounds

Charges on Monatomic Ions 1+ 2+ 3+ 3- 2- 1-

Charges on Transition Metals Ag 1+ Zn 2+ Cu 1+ or 2+ Fe/Cr 2+ or 3+ Sn 2+ or 4+ Pb 2+ or 4+ See list.

Charges of Metals PbO2 and PbO

Polyatomic Ions Page 226

Ionic Compounds Formulas Write the symbols Determine the charges Monatomic ions from the periodic table Transition metals from a roman numeral Polyatomic ions from sheet. Cross the charges. Reduce to lowest ratio.

Ionic Compounds Names Write the cation name. Write the anion name. Add –ide to the anion if monatomic Add the roman numeral for any transition metal. NO PREFIXES!!!!

Ionic Binary Compounds Aluminum Oxide FORMULAS 3+ 2- Al O 3 2 (3+ x ) + (2- x ) = 0 2 3 Al2O3 (charge x subscript)+(charge x subscript) = 0

Ionic Binary Compounds Aluminum Oxide FORMULAS 3+ 2- Al O 3 2 REDUCE IF NECESSARY!! Al2O3

Ionic BinaryCompounds NAMING Mg3N2 NO PREFIXES!! Magnesium Nitrogen ide

1. Write formulas for the binary ionic compounds formed between the following elements: a. potassium and iodine b. magnesium and chlorine c. sodium and sulfur d. aluminum and sulfur e. aluminum and nitrogen 2. Name the binary ionic compounds indicated by the following formulas: a. AgCl e. BaO b. ZnO f. CaCl2 c. CaBr2 d. SrF2 Practice Page 223

Ionic Compounds with Transition Metals FORMULAS Iron (III) Chloride 3+ 1- Fe Cl 1 3 (3+ x ) + (1- x ) = 0 1 3 FeCl3

Ionic Compounds with Transition Metals FORMULAS Tin (II) Oxide 2+ 2- Sn O 1 1 (2+ x ) + (2- x ) = 0 1 1 SnO

Ionic Compounds with Transition Metals FORMULAS Tin (II) Oxide 2+ 2- Sn O 2 1 1 2 REDUCE! SnO

1. Write the formula and give the name for the compounds formed between the following ions: a. Cu 2+ and Br − d. Hg 2+ and S 2− b. Fe 2+ and O 2− e. Sn 2+ and F − c. Pb 2+ and Cl − f. Fe 3+ and O 2− 2. Give the names for the following compounds: a. CuO c. SnI4 b. CoF3 d. FeS Practice Page 225

Ionic Compounds with Transition Metals NAMING PbO ( x 1 ) + ( 2- x 1 ) = 0 2+ NO PREFIXES!! Lead II Oxygen ide

Ionic Compounds with Polyatomic Ions FORMULAS Ammonium Sulfate + 2- (NH ) (SO ) 4 2 4 1 (1+ x ) + (2- x ) = 0 2 1 (NH4)2SO4 Parenthesis are needed if the p. ion has a subscript from the crossed charge – outside the ( ).

Ionic Compounds with Polyatomic Ions NAMING Ca(NO3)2 NO PREFIXES!! Calcium Nitrate

Practice Page 227 1. Write formulas for the following ionic compounds: a. sodium iodide e. copper(II) sulfate b. calcium chloride f. sodium carbonate c. potassium sulfide g. calcium nitrite d. lithium nitrate h. potassium perchlorate 2. Give the names for the following compounds: a. Ag2O b. Ca(OH)2 c. KClO3 d.NH4OH e. Fe2(CrO4)3 f. KClO Practice Page 227

Writing Fomulas and Naming Molecular Compounds

Prefixes for Covalent p. 228

Molecular Compound Formulas Write the symbols. Use prefixes for subscripts. DON’T reduce.

Molecular Compound Names Write the name of the elements. Order: Smaller group number first; Same group? Greater period number first. Add –ide to the second element. Add prefixes to each element for the number of atoms.

Binary Molecular Compounds FORMULAS Disulfur difluoride S F 2 2 DON'T REDUCE! S2F2

Binary Molecular Compounds NAMING O N 2 4 di nitrogen tetra oxygen ide

Practice Page 229 1. Name the following binary molecular compounds: a. SO3 b. ICl3 c. PBr5 2. Write formulas for the following compounds: a. carbon tetraiodide b. phosphorus trichloride c. dinitrogen trioxide Practice Page 229

Acids and Salts Acids – Chapter 14 Binary Acids – two elements; hydrogen and one other element Oxyacids – contain hydrogen, one other element and oxygen Acid – typically thought of as an H donor; usually referred to as a solution of the compound in water.

Acids and Salts Salt – an ionic compound Made from the cation of a base and the anion of an acid Some retain an H in the anion Example: CO3 2- carbonate HCO3 1- hydrogen carbonate or bicarbonate

Salt Definition Animation p. 230

HF, HCl, H3PO4, HNO3, H2SO4 CH3COOH List of Acids Know these acids: HF, HCl, H3PO4, HNO3, H2SO4 CH3COOH p. 230

Section 3 Oxidation Numbers

Oxidation Numbers Oxidation numbers are numbers assigned to the atoms in a molecular compound or ion that indicates the general distribution of electrons among bonded atoms. Oxidation numbers are not actual charges. Oxidation numbers can be useful in naming compounds and writing formulas. -1 +1 +2 +3 -2

Rules for Assigning Oxidation Numbers Atoms in a pure element have an oxidation number of zero – O2 Ox. # = 0 Fluorine always has ox. # of -1 Oxygen almost always has ox. # of -2 except in peroxides such as H2O2 – then it is a -1.

Rules for Assigning Oxidation Numbers (Rules continued): Hydrogen’s ox. # is +1 unless it is with metals – then it is -1 The sum of the ox. # in molecules must be zero, but in polyatomic ions, it is equal to the ions charge.

Oxidation Numbers What are the oxidation numbers for each atom in these compounds? UF6 : Fluorine is -1 x 6 = -6 Uranium +6 {+6 + (-6)} = 0 H2SO4 : Oxygen is -2 (x 4 = -8) Hydrogen is +1 (x 2 = +2) so Sulfur has to be +6 { (+6) + (+2) + (-8) }= 0

Oxidation Numbers What are the oxidation numbers for the chlorate polyatomic ion? ClO3- : Oxygen is -2 x 3 = -6 Chlorine must be +5 { (+5) + (-6)} = -1 (the ion’s charge)

Using Chemical Formulas Section 4 Using Chemical Formulas

Formula Mass With a chemical formula, you can calculate many characteristic values for a compound. Formula Mass: Compounds have masses – just like elements.

Formula Mass Formula Mass: The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula. To find the mass of a compound simply add the masses of the atoms that make up the compound. Units are amu’s.

Formula Mass To find the formula mass of sulfuric acid (H2SO4): element # of atoms x mass (to 2 decimals) H 2 1.01 = 2.02 amu S 1 32.01=32.01 amu O 4 16.00=64.00 amu 98.03 amu

Formula Mass To find the formula mass of Calcium Nitrate Ca(NO3)2 element # of atoms x mass = Ca 1 40.08 =40.08 amu N 2 14.01 =28.02 amu O 6 16.00= 96.00 amu 164.10 amu

Molar Mass Molar Mass The mass of a mole of any substance is equal to its formula mass – except instead of amu’s it is in grams. Formula mass of sulfuric acid = 98.03 amu Molar mass of sulfuric acid = 98.03 grams

Molar Mass To find the molar mass of Calcium Nitrate Ca(NO3)2 element # of atoms x mass = Ca 1 40.08 =40.08 g N 2 14.01 =28.02 g O 6 16.00= 96.00 g 164.10 g

Percentage Composition It is sometimes useful to know what the percentage of a compound is an element. What percentage of water is oxygen? H: 1.01 x 2 = 2.02 O: 16.0 x 1 = 16.0 Molar Mass= 18.02 g 16.0 ÷18.02 = 88.79%

Molar Mass Molar Mass can be used as a conversion factor. 1 mole H2SO4 98.03 grams or 98.03 grams 1 mole H2SO4

Problems How many moles are there in 25 g of H2SO4? 1 mole H2SO4 25 g H2SO4 x = 0.255 mol 98.03 grams

Problems What is the mass of 4.2 moles of H2SO4? x = 1 mol H2SO4 98.03 g H2SO4 4.2 mol H2SO4 x = 411.73 mol 1 mol H2SO4

Problems How many molecules are in 54 g of H2SO4? 6.02 x 1023 molecules H2SO4 54 g H2SO4 = x 98.03 g H2SO4 3.32 x 1023 molecules

Determining Chemical Formulas Section 4 Determining Chemical Formulas

Chemical Formula from % Comp Check periodic table for molar masses of each element Find moles of each element present (assume 100g since we are working with percentages) To determine the simplest ratio of moles in the compound, select the smallest number of moles calculated and divide the other moles calculated by that number Write the formula using the smallest whole number ratio of elements

Empirical formulas Simplest formula Consists of element symbols and subscripts showing the numbers of each element Really, subscripts represent the smallest whole number ratios

Empirical formulas What is the empirical formula of a compound containing 56.6% K, 8.7% C and 34.7 % O ? K= 39.10 g/mol C = 12.01 g/mol O = 16.00 g/mol

Empirical formulas K 56.6 g K x 1 mol K = 1.45 mol 39.10 g K C 8.7 g C x 1 mol C = 0.724 mol 12.01 g C O 34.7 g O x 1 mol O = 2.17 mol 16.00 g O Smallest value = 0.724 Divide all answers by this number.

Empirical formulas K = 1.45 mol = 2.00 0.724 mol C = 0.724 mol = 1.00 O = 2.17 mol = 3.00 Therefore, the empirical formula = K2CO3 Name? Potassium Carbonate

Molecular formulas Gives the type and actual number of atoms in the compound CH2O – empirical formula for glucose C6H12O6 – molecular formula for glucose So far, we have been studying ionic compounds, so molecular and empirical formulas were the same In most compounds, however, not the same

Molecular formulas Molecular formulas can be determined from empirical formulas X (empirical formula) = molecular formula (X is a whole number) Also true . . . Molecular molar mass = X Empirical molar mass

Molecular formulas Empirical formula of mercury (I) chloride is HgCl. What is the molecular formula, knowing that molar mass is 472.08 g/mol? Empirical formula HgCl Molar mass of unknown = 472.08 g/mol 1 mol Hg = 200.59 g/mol 1 mol Cl = 35.45 g/mol Molar mass of HgCl = 236.04 g/mol

Molecular formulas 472.08 g/mol = 2.00 236.04 g/mol 2(HgCl) = Hg2Cl2 Name? dimercury dichloride