Chapter 2 Atoms, Molecules, and Ions General Chemistry: An Integrated Approach Hill, Petrucci, 4 th Edition Mark P. Heitz State University of New York

Chapter 2Atoms, Molecules, and Ions

General Chemistry: An Integrated Approach

Hill, Petrucci, 4th Edition

Mark P. HeitzState University of New York at Brockport

© 2005, Prentice Hall, Inc.

Chapter 2: Atoms, Molecules, and Ions

2

Example: Decomposition of mercuric oxide (HgO)

Laws of Chemical Composition

Conservation of Mass - The total mass remains constant during a chemical reaction.

EOS

HgO(s) = Hg(l) + O2(g)


3

Law of Definite Proportions

All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present

EOS

Water always contains:~89% oxygen

~11% hydrogen


4

Basic Copper Carbonate

EOS


5

Law of Multiple Proportions

EOS

When two or more different compounds of the same two elements are compared, the masses of one element that combine with the a fixed mass of the second element are in the ratio of small whole numbers.

Multiple proportions illustrated


6

Law of Multiple Proportions

EOS


7

Atomic Theory of Matter

• All matter is composed of extremely small, indivisible particles called atoms

• All atoms of a given element are alike in mass and other properties, but atoms of one element differ from the atoms of every other element

• Compounds are formed when atoms of different elements unite in fixed proportions

• A chemical reaction involves a rearrangement of atoms. No atoms are created, destroyed, or broken apart in a chemical reaction

EOS


8

Atomic Theory Illustrated …

Note the laws of constant composition and conservation of mass

EOS


9

Subatomic Particles

Protons and neutrons are located at the center of an atom called the nucleus.

Electrons are dispersed around the nucleus.

EOS


10

Isotopes

Atoms that have the same number of protons but different numbers of neutrons are called isotopes

Atomic number (Z) = number of protons

EOS

Hydrogen has 1 proton, 0 neutrons - Z = 1Deuterium has 1 proton, 1 neutron - Z = 1Tritium has 1 proton, 2 neutrons - Z = 1


11

Other Examples of Isotopes

Carbon-14 Z = 6 so 8 neutrons

EOS

The number of neutrons = A – Z

Chlorine-35 Z = 17 so 18 neutrons

Uranium-234 Z = 92 so 142 neutrons


12

Atomic Masses

EOS


13

Atomic Masses

EOS

An atomic mass unit (amu) is defined as exactly one-twelfth the mass of a carbon-12 atom

1 u = 1.66054 × 10–24 g

The atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes of that element


14

Periodic Table

Arranged the known elements in order of increasing atomic weight from left to right and from top to bottom in groups.

EOS

Elements that tend to most closely resemble each other are arranged in the same vertical group.


15

Modern Periodic Table

Elements are divided into two main classes

EOS


16


Except for hydrogen, those elements to the left of the line are metals

EOS


17


Elements to the right of the line are nonmetals

EOS


18


Elements around the line are referred to as metalloids

EOS


19

Introduction to Compounds

A molecule is a group of two or more atoms held together by covalent bonds.

EOS

A chemical formula is a symbolic representation of the composition of a compound in terms of its constituent elements.


20

Molecular Compounds

EOS

Ball-and-stick model vs. Space-filling model


21

Empirical and Molecular Formulas

EOS

Empirical formula: the simplest whole number ratio of elements in a compound

Example: Molecular formula of glucose – C6H12O6

EOS

The elemental ratio C:H:O is 1:2:1, so the empirical formula is CH2O


22

Structural Formulas

EOS

Shows how atoms are attached to one another.


23


24


25


26

Binary Molecular Compounds

Compounds that are typically comprised of two nonmetallic elements:

e.g., CO, NO, HF

EOS

Molecular formulas are usually written with the more “metallic” first – “metallic” means farther left in the period and lower in the group


27

Binary Molecular Formulas

EOS

The lines trace a continuous path from boron (B) to fluorine (F). The element closer to the beginning of this path is generally written first in the formula of a binary molecular compound.


28

Formulas and Subscripts

Subscripts are used when a given atom is used more than once

e.g., H2O, CO2, N2O, HF, B2O3

The presence of subscripts is reflected in the names of compounds

EOS


29

Names of Binary Compounds

The compound name consists of two words, one for each element in the compound

Consider the compounds CO and CO2

Name the element that appears first in the formula: CARBON

The second element has an altered name: retain the stem of the element name and replace the ending by -ide

OXYGEN OXIDE

EOS

However, both compounds cannot be carbon oxide


30

Names of Binary Compounds

The names are further modified by adding prefixes to denote the numbers of atoms

Consider the compounds CO and CO2

EOS


31

Ions and Ionic Compounds

Atoms that gain or lose electrons are called ions

Positive ions: CATIONS Negative ions: ANIONS

Atoms that lose electrons form cations

Na Na+ + e–

EOS

Atoms that gain electrons form anions

Cl + e– Cl–


32

Monatomic Ions

Group A metals usually lose the number of electrons equal to their Group number.

Nonmetal atoms usually gain electrons and have a charge equal to their Group number minus eight.

The periodic table cannot be used to determine the charge on Group B metals.

EOS

For naming, Group B metals capable of multiple charges have the corresponding Roman numeral in parentheses added after the element name.


33

Common Monatomic Ions

EOS


34

Names and Formulas forIonic Compounds

Ionic compounds form when oppositely charged ions are attracted to each other NaCl

Resulting compound is electrically neutral

Na+ Cl–

(+1) + (–1) = 0

Ionic compound names use the cation name followed by the anion name

EOS

Sodium chloride


35

Polyatomic Ions

EOS

Polyatomic ions are charged groups of covalently bonded atoms


36

Hydrates

A hydrate is an ionic compound in which the formula unit includes a fixed number of water molecules associated with cations and anions

EOS

Examples:

BaCl2 . 2 H2O

CuSO4 . 5 H2O


37

Acids

• Taste sour• Turn blue litmus paper red• React with metals to form

hydrogen gas• Neutralize a base

EOS

IntroToAcids


38

Bases

• Taste bitter• Turn red litmus paper blue• Feel slippery on skin• Neutralize an acid

EOS

IntroToBases


39

Arrhenius Concepts

EOS

Acids are compounds that ionize in water to form a solution of H+ ions and anions

Bases are compounds that ionize in

water to form solutions of OH– and cations

Acids and bases react to form a salt and water= neutralization


40

Arrhenius Concepts

Acids and bases react to form a salt and water= neutralization

HCl + NaOH “Salt” + Water

Acid Base Na

cationEOS

HOHCl

/anion


41

Formulas and Names for Acids

Binary acids start with hydro and end with “ic” plus the word acid

EOS

Ternary acids simply use the polyatomic anion name with “ate” changing to “ic” plus the word acid


42

Formulas and Names for Bases

Arrhenius bases always have hydroxide ions

The name follows ionic compound convention

e.g., NaOH – sodium hydroxide

EOS

Molecular bases form OH– after reacting with water

NH3 + HOH NH4OH

Ammonia ammonium hydroxide


43

Formulas and Names for Salts

EOS

Binary salts use the “ide” ending on the anion namee.g., sodium chloride

Polyatomic salts use “ate” ending on the anion namee.g., sodium sulfate


44

Electrolytic Dissociation and Conduction

Molten (liquid) ionic compounds and aqueous solutions of ionic compounds are good electrical conductors: they form cations and anions in solution

EOS

Electrons can flow in these solutions, resulting in an electric current


45

Nonelectrolyte Solutions

Solutions of nonelectrolytes don’t conduct electricity since the solute is exclusively as molecules

EOS

Electrolytes and Nonelectrolytes


46

Strong/Weak Electrolytes

Strong electrolytes generate ions and are good conductors of electricity

EOS

Weak electrolytes partially ionize and are poor conductors of electricity


47

Ion Concentrations in Solutions

Brackets [ ] are used to represent molar concentrations in units of molarity, moles per liter, MIn a 0.010 M solution of NaCl:

Since NaCl(s) Na+(aq) + Cl–(aq)in solution there is 0.010 M Na+

and 0.010 M Cl–

In a 0.010 M solution of Na2SO4:

EOS

Na2SO4(s) 2 Na+(aq) + SO4–2(aq)

in solution there is 0.020 M Na+ and 0.010 M SO4–2

Dissolution Video


48

Strong and Weak Acids

The dissociation of a weak acid in solution is written using a double arrow to indicate that the dissociation does not go to completion

EOS

Strong acids are acids that are completely ionized in water and are good conductors of electricity

Weak acids are acids in which only some of the molecules are ionized in water; the rest remain as intact molecules

Introduction toAcids Clip


49

Limited Ionization

Organic acids such as acetic acid are typical weak acids that have limited ionization in solution

CH3COOH(aq) CH3COO–(aq) + H+(aq)

EOS

+


50

Recognizing Strong/Weak AcidsMolecular formulas of compounds with ionizable H atoms have the H atom written first – strong acids

e.g., HCl, H2SO4

EOS

Condensed structural formulas for weakly ionizable H atoms show the H at the end – weak acids

e.g., CH3COOH


51

Recognizing Strong/Weak Acids

EOS

Memorize the six strong acids


52

Strong and Weak Bases

• Strong bases are ionic hydroxides that completely ionize in water - good conductors of electricity

• Weak bases are substances that act as bases but remain mostly molecular at equilibrium in water

• The dissociation of a weak base in solution is written using a double arrow to indicate that the dissociation does not go to completion

EOS

Ammonia, NH3, is a weak base


53

Recognizing Strong/Weak Bases

As with acids, memorize the few strong bases

EOS


54

Organic Compounds

• Organic Chemistry is the study of carbon and its compounds

• Carbon compounds containing one or more of the elements H, O, N, or S are especially common

• Most organic compounds are molecular compounds

• Can exist as acids, bases, and salts• Compounds have systematic names AND

common names

EOS


55

Representations of Molecules

EOS

Condensed Structural Formula CH3CH2CH3

Structural Formula

Ball and Stick


56

Saturated Hydrocarbons

Hydrocarbons have only hydrogen and carbon atoms Saturated hydrocarbon:

has the maximum number of hydrogen atoms possible for each carbon atom

EOS

Alkanes are saturated hydrocarbons

Methane (CH4) is the first molecule in the alkane series


57

Prefixes for Number of Carbon

Used for simple organic molecules

Combined with alkane ending “ane”

e.g., propane is a 3-carbon alkane

EOS


58

Table 20.2


59

Ethane Propane

• Second most simple alkane

• Minor ingredient of natural gas

• Also known as bottled gas

• Found in natural gas, but separately for commercial purposes

C C

H

H

H

H

H

H

C C

H

H

H

H

H

H

C

H

H


60

Butane

• Gas used in Butane lighters• Four carbon chain allows

for possible isomerizations- Compounds which share

the same molecular formula but differ in their structural formula

C

H

H

H

C

H

H

C

H

H

HC

H

H

C

H

H

H

C

H

C

HCH

H

HH

H


61

Isomers

EOS

Compounds with the same molecular formula but different structural formulas


62

Cyclic Alkanes

Alkane compounds that have carbons arranged in a ring structure are called cycloalkanes.

use the prefix cyclo-

methylcyclopropane

EOS

cyclohexane


63

Ethene

• Simplest member if the alkene family, also called ethylene

• Most important commercial organic chemical

• U.S. production over 20 billion kg, more than have is used in the production of polyethylene, one of the most familiar plastics.

C C

H

H

H

H


64

Higher Level Alkenes

• alkenes of containing four carbons provide the opportunity for isomerization, a change in the location of the double bond.

• Different double bond positions result in different chemical properties

C

H

H

C

H

C

H

H

HC

H

H

C

H

H

H

C

H

C

H

H

HC

H


65

Ethyne

• Commercially known as acetylene

• Used as a fuel in welding torches

• Past used a surgical anesthetic

C C HH


66

Functional Groups

• Alcohols• Ethers• Carboxylic Acids• Esters• Amines

Specific groupings of atoms attached to a carbon chain that give the compound unique properties

EOS

Most-common functional groups include:


67

Table 20.5


68

Alcohols

EOS

Alcohols are molecules that contain a hydroxyl group (OH)


69

Ethanol• Alcohol found in wine, liquor or beer• Industrial ethanol made from ethene is cheaper

because it generally lacks the same taxes on the “recreational” alcohol

• Although identical, industrial contains a noxious substance to prevent people from drinking it.

• A solution of 70% ethanol by volume acts as an antiseptic by coagulating bacterial proteins

C C

H

OH

H

H

H

H


70

Iso-propanol

• Commonly called rubbing alcohol• Used to give sponge baths to reduce high fevers.• Alcohol quickly evaporates removing heat from

the skin surface, lowering one’s temperature

C C

H

H

H

H

H

H

C

H

OH


71

Propanetriol

• Commonly known as glycerol, or glycerin• Very think, sweet tasting compound• Nontoxic, excellent carrier of medicine• Used by cosmetic industry in hand and skin creams

because it acts as a good lubricant

C C

OH

H

H

HO

H

H

C

H

OH


Aldehyde

Ketone

O

CR H

R = H, alkyl, aryl

O

CR R'

R and R' = alkyl or arylR and R' cannot be hydrogen!

STRUCTURE


CH3

CCH2

CH2CH3

O

2-Pentanone

EXAMPLES

O

CCH2 CH

CH3 CH2

CH2

CH3

CH3

4-Ethyl-3-hexanone


CH3

CCH2

CH2CH3

O

Methyl propyl ketone

Example of Common NamesExample of Common Names

O

CCH2 CH2

CH3 CH3

Diethyl ketone


• Choose the longest continuous carbon chain that contains the carbonyl carbon

• Number from the end of the chain closest to the carbonyl carbon (carbon #1!)

• Aldehyde ending is -al

IUPAC Nomenclature of AldehydesIUPAC Nomenclature of Aldehydes

Do the aldehydes section of Organic Nomenclatureprogram.


EXAMPLES

CH3

CH2CH2

CH2C

O

Hpentanal

CH3CH

CHC

O

HCH3

Cl

2-chloro-3-methylbutanal

12

34

always carbon 1aldehyde group is


O

CH H

O

CH CH3

C

O

H

SPECIAL CASESSPECIAL CASES

formaldehyde

acetaldehyde

benzaldehyde

KNOWTHESE


78

Ethers

Ethers are molecules in which two alkane groups (R-) are attached to a central oxygen atom

The general formula is R-O-R´

R and R´ may be the same or different groups

EOS

CH3CH2OCH2CH3

CH3CH2OCH2CH2CH3


79

Carboxylic Acids

EOS

Carboxylic acids are alkanes that also contain a carboxyl group and are weak acids

HCOO– + H+

Acts like an Arrhenius acid, loses a hydrogen ion


80

Esters

Esters are molecules in which two alkanes are attached to each side of a carboxyl group (R’-COO-R)

EOS


81

NH2(CH2)4NH2

Amines

Amines are molecules in which alkanes and hydrogen(s) are attached to a central nitrogen

EOS

Amines are weak bases


82

Summary of Concepts

EOS

• The basic laws of chemical combination are the laws of conservation of mass, constant composition, and multiple proportions.

• The three main subatomic particles are the protons, neutrons, and electrons.

• Atoms with the same number of protons but different numbers of neutrons are called isotopes.

• A chemical formula indicates the relative numbers of atoms of each type in a compound.


83

Summary (cont.)

EOS

• The periodic table is an arrangement of the elements by atomic number that places elements with similar properties into the same vertical group.

• Ions are formed by the gain or loss of electrons. Positive ions are cations and negative ions are anions.

• Many compounds are classified as either acids (H+), bases

(OH–), or salts (neutralization of acid and base).

• Organic compounds are based on the element carbon.

• Functional groups confer distinctive properties on an organic molecule.

Documents

Chapter 2 Atoms, Molecules, and Ions General Chemistry: An Integrated Approach Hill, Petrucci, 4 th Edition Mark P. Heitz State University of New York