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Chapter Two:
ATOMS, MOLECULES, AND IONS
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 2
Early History of Chemistry
• Greeks were the first to attempt to explain why chemical changes occur.
• Alchemy dominated for 2000 years:– Several elements discovered– Mineral acids prepared
• Robert Boyle was the first “chemist”:– Performed quantitative experiments
2.1
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 3
Three Important Laws
• Law of conservation of mass (Lavoisier):– Mass is neither created nor destroyed
• Law of definite proportion (Proust):– A given compound always contains exactly the
same proportion of elements by mass
2.2
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 4
Three Important Laws (continued)
• Law of multiple proportions (Dalton):– When two elements form a series of
compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers
– http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/003_MULTIPLEPROP.MOV
2.2
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 5
Dalton’s Atomic Theory (1808)
• Each element is made up of tiny particles called atoms.
2.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 6
Dalton’s Atomic Theory (continued)
• The atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.
2.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 7
Dalton’s Atomic Theory (continued)
• Chemical compounds are formed when atoms of different elements combine with each other. A given compound always has the same relative numbers and types of atoms.
2.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 8
Dalton’s Atomic Theory (continued)
• Chemical reactions involve reorganization of the atoms—changes in the way they are bound together.
• The atoms themselves are not changed in a chemical reaction.
2.3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 9
Concept Check
Which of the following statements regarding Dalton’s atomic theory are still believed to be true?
I. Elements are made of tiny particles called atoms.
II. All atoms of a given element are identical.
III. A given compound always has the same relative
numbers and types of atoms.
IV. Atoms are indestructible.
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 10
Early Experiments to Characterize the Atom
• J. J. Thomson (1898-1903):– Postulated the existence of electrons using
cathode-ray tubes– Determined the charge-to-mass ratio of an
electron– The atom must also contain positive particles
that balance exactly the negative charge carried by the electrons
2.4
Figure 2.8 Deflection of Cathode Rays by an Applied Electric Field
Figure 2.9 The Plum Pudding Model of the Atom
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 13
Early Experiments to Characterize the Atom
• Robert Millikan (1909):– Performed experiments involving charged oil
drops– Determined the magnitude of the electron
charge– Calculated the mass of the electron
2.4
Figure 2.10 A Schematic Representation of the Apparatus Millikan Used to Determine
the Charge on the Electron
Milikan’s Experiment
• http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/004_MILLIKANOIL.MOV
• Perform Millilkan’s Experiment yourself– http://webphysics.davidson.edu/applets/pqp_pr
eview/contents/pqp_errata/cd_errata_fixes/section4_5.html
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 15
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 16
Early Experiments to Characterize the Atom
• Ernest Rutherford (1911):– Explained the nuclear atom– Atom has a dense center of positive charge
called the nucleus– Electrons travel around the nucleus at a
relatively large distance
2.4
Figure 2.12 Rutherford's Experiment On a-Particle Bombardment of Metal Foil
Rutherford’s experiment
• http://micro.magnet.fsu.edu/electromag/java/rutherford/
• Animation with narration– http://cwx.prenhall.com/petrucci/medialib/medi
a_portfolio/text_images/006_RUTHERFORD.MOV
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 18
Rutherford’s Observations
• Most α particles passed straight through the foil
• Some α particles were deflected to the side
• A few α particles were bounced backward
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 19
Figure 2.13 a & b (a) Expected Results of the Metal Foil Experiment
if Thomson's Model Were Correct (b) Actual Results
Rutherford’s Conclusions
• Atoms are mostly empty space
• Atoms contain positively charged particles
• Atoms contain a dense nucleus
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 21
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 22
The Modern View of Atomic Structure-Nuclear Model
• The atom contains: Electrons Protons – found in the nucleus; positive charge
equal in magnitude to the electron’s negative charge
Neutrons – found in the nucleus; no charge; virtually same mass as a proton
2.5
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 23
The Modern View of Atomic Structure
• The nucleus is:– Small compared with the overall size of the
atom– Extremely dense; accounts for almost all of the
atom’s mass
2.5
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 24
Nuclear Atom Viewed in Cross Section
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 25
The Modern View of Atomic Structure
• Isotopes:– Atoms with the same number of protons but
different numbers of neutrons– Show almost identical chemical properties;
chemistry of atom is due to its electrons– In nature most elements contain mixtures of
isotopes
2.5
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 26
Two Isotopes of Sodium
2.5
Isotope Symbols
XAZ
• X = Element symbol
• Z = Atomic Number = number of protons
• A = Mass Number = protons + neutrons
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 27
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 28
Exercise
A certain isotope X contains 54 electrons and 78 neutrons.
What is the mass number of this isotope?
What is the symbol of this isotope?
2.5/2.6
Ions
• Atoms that have gained or lost electrons
• Gained electrons– Negative charge– Anion
• Lost electrons– Positive charge– Cation
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 29
• Cations
• Mg2+
– Lost 2 electrons
• K+ – Lost 1 electron
• Anions
• F-
– Gained 1 electron
• S2-
– Gained 2 electrons
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 30
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 31
Chemical Bonds
• Covalent Bonds: – Bonds form between atoms by sharing
electrons– Resulting collection of atoms is called a
molecule
2.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 32
Covalent Bonding
2.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 33
Chemical Bonds
• Ionic Bonds: Bonds form due to force of attraction between
oppositely charged ions Ion – atom or group of atoms that has a net
positive or negative charge Cation – positive ion; lost electron(s) Anion – negative ion; gained electron(s)
2.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 34
Molecular vs. Ionic Compounds
2.6
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 35
The Periodic Table
• Metals vs. Nonmetals
• Groups or Families – elements in the same vertical columns– Alkali metals, alkaline earth metals, halogens,
and noble gases
• Periods – horizontal rows of elements
2.7
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 36
The Periodic Table
2.7
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 37
Naming Compounds
• Binary Compounds:– Composed of two elements
• Binary Ionic Compounds:– Metal-nonmetal
• Binary Covalent Compounds:– Nonmetal to nonmetal
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 38
Binary Ionic Compounds (Type I)
• Cation is always named first and the anion second.
• Monatomic cation has the same name as its parent element.
• Monatomic anion is named by taking the root of the element name and adding –ide.
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 39
Binary Ionic Compounds (Type I)
• Examples:
KCl Potassium chloride
MgBr2 Magnesium bromide
CaO Calcium oxide
2.8
Chemical Formulas
• Identify the elements present– Element symbols
• Identify the number of each atom– Subscripts
• Aluminum sulfide Al2S3
– 2 Al atoms for every 3 S atoms
Writing the Formulas from the Names
–Determine the ions present
–Determine the charges on the cation and anion
–Balance the charges to get the subscripts
Writing the Formulas from the Names (cont.)
• Magnesium chloride– Mg2+ Cl-
– Total positive charge must equal total negative charge
– 1 Mg2+ will balance 2Cl-
– MgCl2
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 43
Polyatomic Ions
• Ions consisting of two or more covalently bonded atoms
• Examples of compounds containing polyatomic ions:
NaOH Sodium hydroxide
Mg(NO3)2 Magnesium nitrate
(NH4)2SO4 Ammonium sulfate
2.8
Compounds Containing Polyatomic Ions
• Polyatomic ions are charged entities that contain more than one atom
• Polyatomic compounds contain one or more polyatomic ions
• Name polyatomic compounds by naming cation and anion
• Al(C2H3O2)3 = aluminum acetate
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 45
Binary Ionic Compounds (Type II)
• Metals in these compounds form more than one type of positive charge.
• Charge on the metal ion must be specified.
• Roman numeral indicates the charge of the metal cation.
• Transition metal cations usually require a Roman numeral.
2.8
Determining the Charge on a Cation – Au2S3
• Determine the charge on the anion– Sulfide = -2
• Determine the total negative charge– (-2) x 3 = -6
• Total positive charge = total negative charge
• Divide total positive charge by the number of cations– +6/2 = +3
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 47
Binary Ionic Compounds (Type II)
• Examples:
CuBr Copper(I) bromide
FeS Iron(II) sulfide
PbO2 Lead(IV) oxide
2.8
Type IIBinary Ionic Compounds (cont.)
¶Old naming system
¶Uses root name or latin name for metal
¶Uses suffixes instead of roman numerals
Type IIBinary Ionic Compounds (cont.)
¶Suffixes
¶_____ic for higher charge
¶_____ous for lower charge
Type IIBinary Ionic Compounds (cont.)
¶Examples
¶Iron (III) chloride = ferric chloride
¶Iron (II) chloride = ferrous chloride
Type IIBinary Ionic Compounds (cont.)
¶Common latin names
¶Cu – cupric, cuprous
¶Pb – plumbic, plumbous
¶Sn – stannic, stannous
¶Fe – ferric, ferrous
Writing the Formulas from the Names (cont.)
• For Type II
Determine the charges on the cation and anion
• Charge on cation = roman numeral
–Balance the charges to get the subscripts
Writing the Formulas from the Names (cont.)
• Copper (I) oxide– Cu+1 O-2
– 2 Cu+1 will balance 1 O-2
– Cu2O
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 54
Formation of Ionic Compounds
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 55
Binary Covalent Compounds (Type III)
• Formed between two nonmetals.• First element is named first, using the full
element name.• Second element is named as if it were an
anion.• Prefixes are used to denote the numbers of
atoms present.• Prefix mono- is never used for naming the
first element.2.8
Table 2.6 Prefixes Used to Indicate Number in Chemical Names
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 57
Binary Covalent Compounds (Type III)
• Examples:
CO2 Carbon dioxide
SF6 Sulfur hexafluoride
N2O4 Dinitrogen tetroxide
2.8
Writing the Formulas from the Names
• For Type III compounds, use the prefixes to determine the subscripts
• Carbon tetrachloride = CCl4
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 59
Overall Strategy for Naming Chemical Compounds
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 60
Flowchart for Naming Binary Compounds
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 61
Acids
• Acids can be recognized by the hydrogen that appears first in the formula—HCl.
• Molecule with one or more H+ ions attached to an anion.
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 62
Acids
• If the anion does not contain oxygen, the acid is named with the prefix hydro- and the suffix -ic.
• Examples:
HCl Hydrochloric acid
HCN Hydrocyanic acid
H2S Hydrosulfuric acid
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 63
Acids
• If the anion does contain oxygen:– The suffix -ic is added to the root name if the
anion name ends in -ate.
• Examples:
HNO3Nitric acid
H2SO4 Sulfuric acid
HC2H3O2 Acetic acid
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 64
Acids
• If the anion does contain oxygen:– The suffix -ous is added to the root name if the
anion name ends in -ite.
• Examples:
HNO2Nitrous acid
H2SO3 Sulfurous acid
HClO2 Chlorous acid
2.8
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 65
Flowchart for Naming Acids
Copyright © Houghton Mifflin Company. All rights reserved.Chapter 2 | Slide 66
Exercise
Which of the following compounds is named incorrectly?
a) KNO3 potassium nitrate
b) TiO2 titanium(II) oxide
c) Sn(OH)4 tin(IV) hydroxide
d) PBr5 phosphorus pentabromide
e) CaCrO4 calcium chromate
2.8