Elements and Compounds elements combine together to make an almost limitless number of compounds the properties of the compound are totally different from the constituent elements H2(g) + O2(g)  H2O(l) Tro, Chemistry: A Molecular Approach

Tro, Chemistry: A Molecular Approach

Tro, Chemistry: A Molecular Approach

Formation of Water from Its Elements Tro, Chemistry: A Molecular Approach

Allotropes:one of two or more forms of an element that differ in their basic structure diamond graphite Tro, Chemistry: A Molecular Approach

Allotropes of carbon diamond graphite Tro, Chemistry: A Molecular Approach

Allotrope of carbon

Chemical Bonds compounds : made of atoms held together by chemical bonds Bonds:forces of attraction between atoms attractions between protons and electrons Tro, Chemistry: A Molecular Approach

Bond Types two general types of bonding ionic and covalent ionic bonds electrons transferred between atoms, results in oppositely charged ions that attract each other Metals + nonmetal covalent bonds two atoms share some of their electrons Nonmetal + nonmetal Tro, Chemistry: A Molecular Approach

Molecular View of Elements and Compounds Tro, Chemistry: A Molecular Approach

Homonuclear vs heteronuclear Tro, Chemistry: A Molecular Approach

Molecular Elements H2 Cl2 Br2 I2 N2 O2 F2 Certain elements occur as 2 atom molecules Rule of 7’s Other elements occur as polyatomic molecules P4, S8, Se8 H2 Cl2 Br2 I2 7 7A N2 O2 F2 Tro, Chemistry: A Molecular Approach

Classifying Materials atomic elements = Fe molecular elements = N2 molecular compounds = H2O ionic compounds = SrCl2 MgCO3 Tro, Chemistry: A Molecular Approach

Representing Compounds with Chemical Formula compounds represented with: chemical formula Type of formula determines amount of information given

Types of Formula Empirical Formula Tells atoms and their ratio do not describe how many atoms, the order of attachment, or the shape the formulas for ionic compounds are empirical

Empirical formula Empirical formula Molecular formula HO __________ C8H8 C6H12O6 _________ Hg2Cl2

Types of Formula

Expanded structural formula vs. condensed structural formula

Formula Mass the mass of an individual molecule or formula unit (FW) amu (D for Dalton) molecular mass or molecular weight (MW or μ) g/mol sum of the masses of the atoms in a single molecule or formula unit mass of 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu Tro, Chemistry: A Molecular Approach

What Is a Mole? Tro, Chemistry: A Molecular Approach

How Big is a Mole? N=6.022x1023 One mole of Marshmallows would cover the entire earth 12 miles high One mole of marshmallows would fill the Grand Canyon and still be enough left over to displace all the water from Lake Michigan and more

Mole = 6.022x1023items Avogadro’s number N

Molar Mass of Compounds the relative masses of molecules can be calculated from atomic masses Formula Mass = 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu since 1 mole of H2O contains 2 moles of H and 1 mole of O Molar Mass = 1 mole H2O = 2(1.01 g H) + 16.00 g O = 18.02 g so the Molar Mass of H2O is 18.02 g/mole Tro, Chemistry: A Molecular Approach

Moles as Conversion factors Moles to molecules or atoms Use Avogadro’s number Ex: How many molecules of water are in 9.01 g of water? Grams to moles Use Molar Mass Ex: How many moles are in 9.01 g of water?

Moles How many molecules of Chlorine are in 19.5 grams of chlorine? How many moles of sodium atoms is 29.0 grams of sodium? Tro, Chemistry: A Molecular Approach

Tro, Chemistry: A Molecular Approach

Molecular formula In 5.0 moles of the compound Mg(H2PO4)2 How many moles of Mg are there?____ How many moles of phosphorus are there?___ How many moles of oxygen are there?______ Tro, Chemistry: A Molecular Approach

Molar mass What is the formula weight (FW) of Mg(H2PO4)2 including units? ________ What is the molar mass (MW or µ) of Mg(H2PO4)2 including units?_________ Tro, Chemistry: A Molecular Approach

Practice - Converting Grams to Molecules How many molecules are in 50.0 g of PbO2? (PbO2 = 239.2 g/mol) Tro, Chemistry: A Molecular Approach

Percent Composition Percentage of each element in a compound Mass of element/mass of compound The percentages may not always total to 100% due to rounding Tro, Chemistry: A Molecular Approach

Find the mass percent of Cl in CCl2F2

Mass Percent as a Conversion Factor the mass percent tells you the mass of a constituent element in 100 g of the compound the fact that CCl2F2 is 58.64% Cl by mass means that 100 g of CCl2F2 contains 58.64 g Cl this can be used as a conversion factor 100 g CCl2F2 : 58.64 g Cl

Example 3.14 – Find the mass of table salt containing 2.4 g of Na Given: Find: 2.4 g Na, 39% Na g NaCl Concept Plan: Relationships: 100. g NaCl : 39 g Na g Na g NaCl Solution: Check: since the mass of NaCl is more than 2x the mass of Na, the number makes sense

Benzaldehyde is 79. 2% carbon. What mass of benzaldehyde contains 19 Benzaldehyde is 79.2% carbon. What mass of benzaldehyde contains 19.8 g of C?

Empirical Formula simplest, whole-number ratio of the atoms of elements in a compound can be determined from elemental analysis masses of elements formed when decompose or react compound combustion analysis percent composition Tro, Chemistry: A Molecular Approach

Finding an Empirical Formula convert the percentages to grams assume you start with 100 g of the compound skip if already in grams convert grams to moles use molar mass of each element write a pseudoformula using moles as subscripts divide all by smallest number of moles if result is within 0.1 of whole number, round to whole number multiply all mole ratios by number to make all whole numbers if ratio ?.5, multiply all by 2; if ratio ?.33 or ?.67, multiply all by 3; if ratio 0.25 or 0.75, multiply all by 4; etc. skip if already whole numbers Tro, Chemistry: A Molecular Approach

Calculating Empirical formula 1. A sample of an unknown compound with a mass of 2.571 g was found to contain 1.102 g of carbon and 1.469 g of oxygen. What is its empirical formula?

Calculating empirical formula An oxide of iron called black iron oxide, is analyzed. In a 2.448 g sample the ore was found to contain 1.771 g of Fe and 0.6766 g of O. Calculate the empirical formula of this compound

Example 3.17 Laboratory analysis of aspirin determined the following mass percent composition. Find the empirical formula. C = 60.00% H = 4.48% O = 35.53%

Finding empirical formula C, H, O mol C, H, O mol ratio empirical formula Tro, Chemistry: A Molecular Approach

Determine the empirical formula of hematite, which contains 72 Determine the empirical formula of hematite, which contains 72.4% Fe (55.85) and the rest oxygen (16.00) Tro, Chemistry: A Molecular Approach

Molecular Formulas The molecular formula is a multiple of the empirical formula To determine the molecular formula you need to know the empirical formula and the molar mass of the compound

Example 3.18 – Find the molecular formula of butanedione empirical formula for butanedione = C2H3O; MW of molecular formula = 86.03 g/mol

Benzopyrene has a molar mass of 252 g/mol and an empirical formula of C5H3. What is its molecular formula? (C = 12.01, H=1.01)

hydrates

Hydrates When the hydrate of RuCl3 is heated water is driven off to form the anhydrous salt as shown below: RuCl3.xH2O  RuCl3 + xH2O If 1.056 g of hydrated compound is heated and 0.838 g of anhydrous salt remains what is the value of x?

Naming hydrates: name the ionic compound then the water part, use prefixes for number of water molecules Ionic formula • x H2O x = prefix (di, tri etc from covalent naming) H2O = hydrate   Ex:   CuSO4• 5 H2O   copper(II) sulfate pentahydrate Ex.   CaCl2• 2 H2O   calcium chloride dihydrate

Combustion Analysis

Example 3.20 Combustion of a 0.8233 g sample of a compound containing only carbon, hydrogen, and oxygen produced the following: CO2 = 2.445 g H2O = 0.6003 g Determine the empirical formula of the compound Tro, Chemistry: A Molecular Approach

Write a Concept Plan: g CO2, H2O mol CO2, H2O mol C, H g C, H g O mol C, H, O mol ratio empirical formula

Information Given: 0.8233 g compound, 2.445 g CO2, 0.6003 g H2O, Find: Empirical Formula, CxHyOz 0.05556 mol C, 0.6673 g C, 0.06662 mol H, 0.06715 g H, 0.0889 g O, 0.00556 mol O Plan: g CO2 & H2O  mol CO2 & H2O  mol C & H  g C + H  g O  mol O  mol ratio  emp. formula Example 3.20: Find the empirical formula of compound with the given amounts of combustion products Tro, Chemistry: A Molecular Approach

The smell of dirty gym socks is caused by the compound caproic acid The smell of dirty gym socks is caused by the compound caproic acid. Combustion of 0.844 g of caproic acid produced 0.784 g of H2O and 1.92 g of CO2. If the molar mass of caproic acid is 116.2 g/mol, what is the molecular formula of caproic acid? (μ C = 12.01, H = 1.008, O = 16.00)

C H O g 0.524 0.0877 0.232 moles 0.0436 0.0870 0.0145 C0.0436H0.0870O0.0145 Tro, Chemistry: A Molecular Approach

Molecular Formula = {C3H6O} x 2 = C6H12O2 Tro, Chemistry: A Molecular Approach

1. Nicotine, a poisonous compound found in tobacco leaves, is 74 1. Nicotine, a poisonous compound found in tobacco leaves, is 74.0% C, 8.65% H, and 17.35% N. It has a molar mass of 162 g/mol. What is the molecular formula of nicotine? 2. The “average” cigarette in the US contains 9.0 mg of nicotine but during smoking about 90% of the nicotine is burned off. How many molecules of nicotine are inhaled during smoking of one “average” cigarette?

Other fun things to do with moles Molarity

What is the molarity of a solution prepared by dissolving 15 What is the molarity of a solution prepared by dissolving 15.0 g of sodium hydroxide in enough water to make a total of 225 mL of solution?

Practice Problems What is the molarity of a solution that contains 1.724 moles of H2SO4 in 2.50 L of solution? 2. What is the molarity of a solution prepared by dissolving 25.0 g of HCl (g) in enough water to make 150.0 mL of solution?

How would you prepare 1 liter of a 0 How would you prepare 1 liter of a 0.25 M (molar) solution of glucose (C6H12O6) (molar mass 180 g/mol)?