Ch03 lecture

Click here to load reader

download Ch03 lecture

of 87

Embed Size (px)

Transcript of Ch03 lecture

PowerPoint Presentation

Catherine E. MacGowanArmstrong State UniversityLecture PresentationChapter 3

Molecules, Compounds, and Chemical Equations

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. TroHydrogen + Oxygen = WaterElements can combine to form compounds.Daltons atomic theoryLaw of definite proportionsLaw of multiple proportionsThe properties of the compound are totally different from the constituent elements.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

2

Chemical BondsCompounds are made of atoms held together by chemical bonds.

Bonds are attraction forces between atoms.The bonding attraction comes from attractions between protons and electrons.

Types of chemical bondsIonicBond formed between a metal and a nonmetal element CovalentBond formed between two nonmetal elementsMetallicBond formed between two metal elements

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

3

Ionic Bonds

Occur between a metal and a nonmetal elementTransfer of electron(s) from one element to anotherA metal atom can transfer an electron to a nonmetal.

Ionic bonding results in the attraction between the two charges (cation plus anion).

The resulting cation and anion are attracted to each other by electrostatic forces.These forces are governed by Coulombs law. Strength of bond can be calculated using Coulombs law.

Compounds formed having ionic bonds are referred to as ionic compounds.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

4

Formation of an Ionic Compound

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

5

What Is Covalent Bonding?It occurs between nonmetal elements.

The bond arises from the mutual attraction of two nuclei for the same electrons. Electron sharing results.

Bond is a balance between attractive forces. (protons of atom A to electrons of atom B) repulsive forces. (electrons of atom A to electrons of atom B) and (protons of atom A to protons of atom B)

Covalently bonded compounds are referred to as molecular compounds.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

6

Chemical FormulasA chemical formula represents the composition of the substance.It indicates the type and number of elements that make up the molecule (compound).

ExampleC2H6O is the chemical formula for ethanol.The compound of ethanol is composed of two moles of carbon atoms, six moles of hydrogen atoms, and one mole of oxygen atoms.

The molecular mass for ethanol is determined from its molecular formula.Ethanols molecular mass is 46.0 grams/mole.One mole of ethanol has a mass of 46.0 grams.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

7

Types of Chemical FormulasMolecular lists the exact number and types of atoms of which the molecule is composed.ExampleThe hydrogen peroxide molecular formula is H2O2.

Empirical lists the relative type and number of atoms in the compound.It is the simplest ratio of atom to atom.Example For the molecule hydrogen peroxide, H2O2, the empirical formula is (HO)n=2, where n means two units of (HO).For every H atom there is one O atom present.

Structural represents how the atoms in the molecule are connected to one another.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

8

Empirical Formulas Empirical formulas do not give information on the compounds shape or how atoms are attached to each other.Empirical formulas may or may not indicate how many of each type of atom is present in the compound.Will if the molecular formula is the empirical formulaExample Water is H2O.Will not if the molecular formula is a multiple of the empirical formula Example Oxalic acid is C2H2O4.The empirical formula for oxalic acid is CHO2.The molecular formula of oxalic acid is C2H2O4, which is two units of CHO2 or (CHO2)n=2.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

9

Types of Chemical FormulasRepresenting the molecule oxalic acid

Molecular C2H2O4

EmpiricalCHO2 or (CHO2)n=2

Structural

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

10

Problem:Determine the empirical formula for the following:An ionic compound that has two aluminum ions for every three oxide ionsHexane, C6H14

3. Arabinose, C5H10O5

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

11

Answer:Determine the empirical formula for the following:Al2O3(CH2O)n where n = 2An ionic compound that has two aluminum ions for every three oxide ions

Hexane, C6H14

3. Arabinose, C5H10O5(C3H7)n where n = 2

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

12

Molecular and Empirical Problems

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

13

Molecular ModelsBall-and-stick models use balls to represent the atoms and sticks to represent the attachments between them.Gray = CarbonWhite = Hydrogen

Space-filling models use interconnected spheres to show the electron clouds of atoms connecting together.

Models depict the three-dimensional structure for the compound methane. Methanes chemical formula is CH4.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

14

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

15

Classification of Elements and CompoundsCompounds composed of a metal element and a nonmetal element are ionic compounds.The cation and/or anion may be simple or polyatomic.ExamplesSimple: chloride ion (Cl), copper(II) ion (Cu2+), silicon(IV) ion (Si4+), or nitride ion (N3)Polyatomic: nitrate ion (NO3) or ammonium ion (NH4+)Their formulas are sometimes referred to as ionic formulas because the bonding in the compound is ionic in nature.

Compounds composed of nonmetal elements are referred to as molecular compounds.Atoms are attached to each other in a molecular compound through covalent bonding.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

16

Classification of Elements and Compounds

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

17

Ionic versus Molecular CompoundsThe compound propane contains individual C3H8 molecules.The sodium chloride molecule, NaCl, is composed of an array of Na+ ions and Cl ions.

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

18

Predicting Formulas for Ionic CompoundsIonic compounds are composed ofmetal + nonmetal elements.metal + nonmetal polyatomic ions.

Chemical formulas of ionic compounds are neutral or have a net charge of zero.

Question: What is the molecular formula for Mn3+ and O2 (oxide ion)?

Mn3+ has an oxidation state of 3+ and the oxide ion has an oxidation state of 2.Multiply the absolute value of the respective oxidation states to derive the molecular formula Mn2O3.

Mn: + 3 2 = + 6O: 2 3 = 6 0

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

19

A List of Common Charges (Oxidation States) Element or GroupCommon Charge (oxidation state)Alkali metals 1+ only Alkaline earth metals+2 onlyHalogensFluorine (F) 1 onlyOther halogens15A column nonmetals36A column nonmetals2Aluminum (Al)+3 onlyHydrogen (H)When combined with a nonmetal+1When combined with a metal1

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

20

List of Common Polyatomic IonsNameFormulaAcetateC2H3O2CarbonateCO32Hydrogen carbonate(aka bicarbonate)HCO3HydroxideOHNitrateNO3NitriteNO2ChromateCrO42DichromateCr2O72AmmoniumNH4+

NameFormulaHypochloriteClOChloriteClO2ChlorateClO3PerchlorateClO4SulfateSO42SulfiteSO32Hydrogen sulfate(aka bisulfate)HSO4Hydrogen sulfite(aka bisulfite)HSO3

2016 Pearson Education, Inc.Instructors Resources Materials (Download Only) for Principles of Chemistry: A Molecular Approach, 3/eNivaldo J. Tro

21