Introductory Chemistry, 2nd Edition Nivaldo Tro Chapter 5 Molecules and Compounds

Molecules and Compounds Compounds = composed of 2 or more elements chemically combined Properties completely different from component elements Salt Sodium (Na) – shiny, reactive, poisonous Chlorine (Cl) – pale yellow gas, reactive, poisonous Sodium chloride (NaCl) – table salt, flavor enhancer Tro's Introductory Chemistry, Chapter 5

Law of Constant Composition Pure substances have constant composition all samples of a pure substance contain same elements in same ratios or proportions regardless of source mixtures have variable composition Tro's Introductory Chemistry, Chapter 5

Compounds Display Constant Composition Water (H2O) decomposed by electrolysis yields 16.0 grams of oxygen to every 2.00 grams of hydrogen. Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0. Tro's Introductory Chemistry, Chapter 5

Formulas Describe Compounds Compound = a distinct substance that is composed of atoms of two or more elements Formulas give the number and type of each atom in the simplest unit of the compound Molecules (H2O) or ions (CaCl2) Number of atoms of each element is written to the right of the element as a subscript if only one atom, 1 subscript is not written Polyatomic groups are placed in parentheses if more than one, i. e. Ca(NO3)2 Tro's Introductory Chemistry, Chapter 5

Formulas Describe Compounds Examples: water = H2O \ two atoms of hydrogen and 1 atom of oxygen table sugar (sucrose) = C12H22O11 \12 atoms of C, 22 atoms of H and 11 atoms O Tro's Introductory Chemistry, Chapter 5

Classifying Materials Atomic elements = elements whose particles are single atoms; Na, Ne, Hg, Ag Molecular elements = elements whose particles are multi-atom molecules; H2, O2, N2, Cl2 Tro's Introductory Chemistry, Chapter 5

Molecular Elements H2 Cl2 Br2 I2 N2 O2 F2 Certain elements occur as 2 atom molecules Rule of 7’s there are 7 common diatomic elements find the element with atomic number 7, N make a figure 7 by going over to Group 7A, then down don’t forget to include H2 H2 Cl2 Br2 I2 VIIA N2 O2 F2 7

Classifying Materials Molecular compounds = compounds whose particles are molecules made of only nonmetals, i.e. CO2 Ionic compounds = compounds whose particles are cations (+) and anions (-), i.e. NaCl Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Molecular Compounds Two or more nonmetals, i.e. H2O, CO2, C6H12O6 Smallest unit is a molecule Tro's Introductory Chemistry, Chapter 5

Order of Elements in a Formula Metals written first NaCl Nonmetals written in order from Table 5.1 CO2 occasional exceptions for historical or informational reasons H2O, but NaOH Order of Listing Nonmetals in Chemical Formulas Table 5.1 F O Cl Br I S H N P C Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Ionic Compounds Metals + nonmetals No individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units Tro's Introductory Chemistry, Chapter 5

Molecular View of Elements and Compounds

Tro's Introductory Chemistry, Chapter 5 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al aluminum chloride, AlCl3 chlorine, Cl2 acetone, C3H6O carbon monoxide, CO cobalt, Co Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Classify each of the following as either an atomic element, molecular element, molecular compound or ionic compound aluminum, Al = atomic element aluminum chloride, AlCl3 = ionic compound chlorine, Cl2 = molecular element acetone, C3H6O = molecular compound carbon monoxide, CO = molecular compound cobalt, Co = atomic element Tro's Introductory Chemistry, Chapter 5

Major Classes of Compounds Ionic metal + nonmetal metal first in formula Binary Ionic compounds with polyatomic ions Molecular 2 nonmetals Binary Molecular (or Binary Covalent) Acids – formula starts with H though acids are molecular, they behave as ionic when dissolved in water may be binary or oxyacid Tro's Introductory Chemistry, Chapter 5

Binary Ionic Compounds: Writing a correct formula 1. Write down the charges of the stable ions with the positive ion first. Ex: for Chlorine and magnesium Mg Cl 2+ 1-

2. Cross-over charges to get subscripts. Drop all +/- signs. Ex: for Chlorine and magnesium Mg Cl 2+ 1 - 1 2

3. Reduce/Simplify subscripts to get the lowest whole number ratio 3. Reduce/Simplify subscripts to get the lowest whole number ratio. The subscript “1” does not have to be shown. Ex: for Chlorine and magnesium MgCl2 Ex: calcium and sulfur Ca+2S-2 Ca2S2 cross-over CaS simplify

How many electrons will an atom lose or gain in an ionic compound? lose 1 e- lose 2 e- lose 3 e- gain 3 e- gain 2 e- gain 1 e-

What will be the charge on the “stable ion” formed? +1 +2 +3 -3 -2 -1

Rules for Naming Ionic Compounds from Formula Made of cation and anion Name by simply naming the ions If cation is: Type I metal (main group) = metal name Type II metal (transition element) = metal name(charge) Polyatomic ion = name of polyatomic ion If anion is: Nonmetal = root of nonmetal name + ide Tro's Introductory Chemistry, Chapter 5

How do you know a metal cation is Type II? Metal Cations Type I metals whose ions can only have one possible charge IA, IIA, (Al, Ga, In) determine charge by position on the Periodic Table IA = +1, IIA = +2, (Al, Ga, In = +3) Type II metals whose ions can have more than one possible charge (transition elements) determine charge by charge on anion How do you know a metal cation is Type II? its not Type I !!! Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, Li copper, Cu gallium, Ga tin, Sn strontium, Sr Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Determine if the following metals are Type I or Type II. If Type I, determine the charge on the cation it forms. lithium, Li Type I +1 copper, Cu Type II gallium, Ga Type I +3 tin, Sn Type II strontium, Sr Type I +2 Tro's Introductory Chemistry, Chapter 5

Determining Charge and Naming Monatomic Nonmetal Anions Determine the charge from position on the Periodic Table To name anion, change ending on the element name to –ide 4A = -4 5A = -3 6A = -2 7A = -1 C = carbide N = nitride O = oxide F = fluoride Si = silicide P = phosphide S = sulfide Cl = chloride Tro's Introductory Chemistry, Chapter 5

Naming Type I Binary Ionic Compounds Contain Metal Cation + Nonmetal Anion Metal listed first in formula & name name metal cation first, name nonmetal anion second cation name is the metal name nonmetal anion named by changing the ending on the nonmetal name to -ide

What is the correct formula and name for a compound made from: 1. nitrogen and potassium 2. magnesium and oxygen 3. chlorine and calcium 4. oxygen and aluminum

1. nitrogen and potassium K3N potassium nitride 2. magnesium and oxygen MgO magnesium oxide 3. chlorine and calcium CaCl2 calcium chloride 4. oxygen and aluminum Al2O3 aluminum oxide

Naming Type II Binary Ionic Compounds Name metal cation first, name nonmetal anion second Metal cation name is the metal name followed by a Roman Numeral in parentheses to indicate its charge determine charge from anion charge Common Type II cations in Table 5.5 Nonmetal anion named by changing the ending on the nonmetal name to -ide Tro's Introductory Chemistry, Chapter 5

Example – Naming Binary Ionic, Type II Metal CuCl Identify Major Class Cu = metal, on left side of Periodic Table Cl = nonmetal, on right side of Periodic Table  Ionic Identify the Subclass 2 elements,  Binary Ionic Is the metal Type I or Type II Cu not in Group IA, IIA, or (Al, Ga, In)  Type II Tro's Introductory Chemistry, Chapter 5

Example – Naming Binary Ionic, Type II Metal CuCl Identify cation and anion Cl = Cl- because it is Group 7 Cu = Cu+ to balance the charge Name the cation Cu+ = copper(I) Name the anion Cl- = chloride Write the cation name first, then the anion name copper(I) chloride Tro's Introductory Chemistry, Chapter 5

Give the formula and name for a compound from Cu+1 and sulfur Cu+1 S-2 formula = Cu2S name = copper(I) sulfide

name = iron(II) chloride Give the formula and name for a compound from Fe+2 and chlorine Fe+2 Cl-1 formula = FeCl2 name = iron(II) chloride Give the formula and name for a compound from Cu+2 and sulfur Cu+2 S-2 formula = CuS name = copper(II) sulfide

What is the formula for copper(II) oxide? Cu+2 O-2 formula = CuO

Compounds with Polyatomic Ions Polyatomic ions are single ions that contain more than one atom Formula: cation first, polyatomic anion or polyatomic cation, monatomic anion Name cation first and then anion Non-polyatomic cations named like Type I and II Non-polyatomic anions named with –ide Polyatomic ions = use name of polyatomic ion Tro's Introductory Chemistry, Chapter 5

Some Common Polyatomic Ions (be able to recognize these) Name Formula and Charge acetate C2H3O2– carbonate CO32– hydrogen carbonate (aka bicarbonate) HCO3– hydroxide OH– nitrate NO3– nitrite NO2– sulfate SO42– chlorate ClO3– ammonium NH4+ Tro's Introductory Chemistry, Chapter 5

Naming Ionic Compounds with Polyatomic Ion Na2SO4 Identify Major Class Na = metal, on the left side of Periodic Table SO4 = is a polyatomic ion,  Ionic Identify the Subclass compound has 3 elements  Ionic with Polyatomic Ion Is the metal Type I or Type II Na is in Group IA,  Type I Tro's Introductory Chemistry, Chapter 5

Naming Ionic Compounds with Polyatomic Ion Na2SO4 Identify the ions Na = Na+ because in Group 1 SO4 = SO42- a polyatomic ion Name the cation Na+ = sodium (Type I) Name the anion SO42- = sulfate Write the name of the cation followed by the name of the anion sodium sulfate Tro's Introductory Chemistry, Chapter 5

Naming Ionic Compounds with Polyatomic Ion Fe(NO3)3 Identify Major Class Fe = metal, on left side of Periodic Table NO3 = is a polyatomic ion because it is in ( )  Ionic Identify the Subclass Have 3 elements  Ionic with Polyatomic Ion Is the metal Type I or Type II Fe not in Group IA, IIA, or (Al, Ga, In)  Type II Tro's Introductory Chemistry, Chapter 5

Naming Ionic compounds with Polyatomic Ion Fe(NO3)3 Identify the ions NO3 = NO3- a polyatomic ion Fe = Fe+3 to balance the charge of the 3 NO3-1 Name the cation Fe+3 = iron(III) (Type II) Name the anion NO3- = nitrate Write the name of the cation followed by the name of the anion iron(III) nitrate Tro's Introductory Chemistry, Chapter 5

Rules for Naming Binary Molecular Compounds Binary molecular compounds = composed of 2 nonmetal elements for binary molecular compound: name first nonmetal then name second nonmetal with ide ending then give each name a prefix to indicate number of atoms (subscript) of each element in formula Tro's Introductory Chemistry, Chapter 5

Naming Binary Molecular Compounds Name first element in formula first use the full name of the element Name the second element in the formula with an -ide as if it were an anion, however, remember these compounds do not contain ions! Use a prefix in front of each name to indicate the number of atoms Never use the prefix mono- on the first element

Tro's Introductory Chemistry, Chapter 5 Subscript - Prefixes 1 = mono-; not used on first nonmetal 2 = di- 3 = tri- 4 = tetra- 5 = penta- 6 = hexa- 7 = hepta- 8 = octa- drop last “a” if name begins with vowel Tro's Introductory Chemistry, Chapter 5

Naming Binary Molecular Compounds BF3 Identify Major Class B = nonmetal, on right side of Periodic Table F = nonmetal, on right side of Periodic Table  Molecular Identify the Subclass 2 elements  Binary Molecular Tro's Introductory Chemistry, Chapter 5

Naming Binary Molecular Compounds BF3 Name the first element: boron Name the second element with an –ide fluorine  fluoride Add a prefix to each name to indicate the subscript monoboron, trifluoride Write the first element with prefix, then the second element with prefix Drop prefix mono from first element boron trifluoride Tro's Introductory Chemistry, Chapter 5

Tro's Introductory Chemistry, Chapter 5 Formula Mass Formula mass = mass of an individual molecule or formula unit also known as molecular mass or molecular weight Sum of the masses of the atoms in a single molecule or formula unit whole = sum of the parts! mass of 1 molecule of H2O = 2(1.01 amu H) + 16.00 amu O = 18.02 amu Tro's Introductory Chemistry, Chapter 5