Atoms, Molecules

1
Chapter 2

• Atoms, Molecules
• Ions

2
Quantum Corral
http//www.almaden.ibm.com/vis/stm/corral.html
3
Scanning Tunneling Microscope
4
Scanning Tunneling Microscope
5
Scanning Tunneling Microscope
6
http//www.cbu.edu/mcondren/SeeAtoms.htm
7
http//mrsec.wisc.edu/
http//mrsec.wisc.edu/
Developed in collaboration with the Institute for
Chemical Education and the Magnetic Microscopy
Center University of Minnesota http//www.physics.
umn.edu/groups/mmc/
8
Sample
http//www.nsf.gov/mps/dmr/mrsec.htm
http//www.nsf.gov/mps/dmr/mrsec.htm
Pull Probe Strip
Pull Probe Strip
9
Which best represents the poles?
(a)
(b)
(c)
North
South
10
Atoms Molecules

• Atoms
• can exist alone or enter into chemical
  combination
• the smallest indivisible particle of an element
• Molecules
• a combination of atoms that has its own
  characteristic set of properties

11
Law of Constant Composition

• A chemical compound always contains the same
  elements in the same proportions by mass.

12
Law of Multiple Proportions

• the same elements can be combined to form
  different compounds by combining the elements in
  different proportions

13
Daltons Atomic Theory

• Postulates
• proposed in 1803
• know at least 2 for first exam

14
Daltons Atomic Theory

• Postulate 1
• An element is composed of tiny particles called
  atoms.
• All atoms of a given element show the same
  chemical properties.

15
Daltons Atomic Theory

• Postulate 2

• Atoms of different elements have different
  properties.

16
Daltons Atomic Theory

• Postulate 3
• Compounds are formed when atoms of two or more
  elements combine.
• In a given compound, the relative number of atoms
  of each kind are definite and constant.

17
Daltons Atomic Theory

• Postulate 4
• In an ordinary chemical reaction, no atom of any
  element disappears or is changed into an atom of
  another element.
• Chemical reactions involve changing the way in
  which the atoms are joined together.

18
Radioactivity
19
Radioactivity

• Alpha helium-4 nucleus
• Beta high energy electron
• Gamma energy resulting from transitions from
  one nuclear energy level to another

20
Alpha Radiation

• composed of 2 protons and 2 neutrons
• thus, helium-4 nucleus
• 2 charge
• mass of 4 amu
• creates element with atomic number 2 lower
• Ra226 ? Rn222 He4(a)

21
Beta Radiation

• composed of a high energy electron which was
  ejected from the nucleus
• neutron converted to proton
• very little mass
• -1 charge
• creates element with atomic number 1 higher
• U239 ? Np239 b-1

22
Gamma Radiation

• nucleus has energy levels
• energy released from nucleus as the nucleus
  changes from higher to lower energy levels
• no mass
• no charge
• Ni60 ? Ni60 g

23
Cathode Ray Tube
24
Thompsons Charge/Mass Ratio
25
Millikins Oil Drop
26
Rutherfords Gold Foil
27
Rutherfords Model of the Atom
28
Rutherfords Model of the Atom

• atom is composed mainly of vacant space
• all the positive charge and most of the mass is
  in a small area called the nucleus
• electrons are in the electron cloud surrounding
  the nucleus

29
Structure of the Atom Composed of

• protons
• neutrons
• electrons

30
Structure of the Atom

• Composed of
• protons
• neutrons
• electrons

• protons
• found in nucleus
• relative charge of 1
• relative mass of 1.0073 amu

31
Structure of the Atom

• Composed of
• protons
• neutrons
• electrons

• neutrons
• found in nucleus
• neutral charge
• relative mass of 1.0087 amu

32
Structure of the Atom

• Composed of
• protons
• neutrons
• electrons

• electrons
• found in electron cloud
• relative charge of -1
• relative mass of 0.00055 amu

33
Size of Nucleus
If the nucleus were 1 in diameter,
the atom would be 1.5 miles in diameter.
34
Ions

• charged single atom
• charged cluster of atoms

35
Ions

• cations
• positive ions
• anions
• negative ions
• ionic compounds
• combination of cations and anions
• zero net charge

36
Atomic number, Z

• the number of protons in the nucleus
• the number of electrons in a neutral atom
• the integer on the periodic table for each element

37
Isotopes

• atoms of the same element which differ in the
  number of neutrons in the nucleus
• designated by mass number

38
Mass Number, A

• integer representing the approximate mass of an
  atom
• equal to the sum of the number of protons and
  neutrons in the nucleus

39
Masses of Atoms

• Carbon-12 Scale

40
Isotopes of Hydrogen H-1, 1H, protium

• 1 proton and no neutrons in nucleus
• only isotope of any element containing no
  neutrons in the nucleus
• most common isotope of hydrogen

41
Isotopes of Hydrogen H-2 or D, 2H, deuterium

• 1 proton and 1 neutron in nucleus

42
Isotopes of Hydrogen H-3 or T, 3H, tritium

• 1 proton and 2 neutrons in nucleus

43
Isotopes of Oxygen

• O-16
• 8 protons, 8 neutrons, 8 electrons
• O-17
• 8 protons, 9 neutrons, 8 electrons
• O-18
• 8 protons, 10 neutrons, 8 electrons

44
The radioactive isotope 14C has how many
neutrons? 6, 8, other
45
The identity of an element is determined by the
number of which particle? protons, neutrons,
electrons
46
Mass Spectrometer
47
Mass Spectra of Neon
48
Measurement of Atomic Masses

• Mass Spectrometer
• a simulation is available at
• http//www.colby.edu/chemistry/
• OChem/DEMOS/MassSpec.html

49
Atomic Masses andIsotopic Abundances

• natural atomic masses
• sum(atomic mass of isotope)
• (fractional isotopic abundance)

50
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?
let x fraction Cl-35
y fraction Cl-37
x y 1
y 1 - x
(AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
Cl-37) 35.453
Thus 34.96885x 36.96590y 35.453
51
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x

52
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453

53
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453

54
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453

55
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453

56
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)

57
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129

58
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129

59
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129
• x 0.7553 ltgt 75.53 Cl-35

60
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129
• x 0.7553 ltgt 75.53 Cl-35
• y 1 - x

61
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129
• x 0.7553 ltgt 75.53 Cl-35
• y 1 - x 1.0000 - 0.7553

62
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129
• x 0.7553 ltgt 75.53 Cl-35
• y 1 - x 1.0000 - 0.7553 0.2447

63
Example Chlorine has two isotopes, Cl-35 and
Cl-37, which have masses of 34.96885 and 36.96590
amu, respectively. The natural atomic mass of
chlorine is 35.453 amu. What are the percent
abundances of the two isotopes?

• let x fraction Cl-35
• y fraction Cl-37
• x y 1 ltgt y 1 - x
• (AW Cl-35)(fraction Cl-35) (AW Cl-37)(fraction
  Cl-37) 35.453
• 34.96885x 36.96590y 35.453
• 34.96885x 36.96590(1-x) 35.453
• (34.96885 - 36.96590)x 36.96590 35.453
• (34.96885 - 36.96590)x (35.453 - 36.96590)
• - 1.99705x - 1.5129
• 1.99705x 1.5129
• x 0.7553 ltgt 75.53 Cl-35
• y 1 - x 1.0000 - 0.7553 0.2447
• 24.47 Cl-37

64
Development of Periodic Table

• Newlands - English
• 1864 - Law of Octaves - every 8th element
  has similar properties

65
Development of Periodic Table

• Dmitri Mendeleev - Russian
• 1869 - Periodic Law - allowed him to
  predict properties of unknown elements

66
Mendeleevs Periodic Table

• the elements are arranged according to increasing
  atomic weights

67
Mendeleevs Periodic Table
Missing elements 44, 68, 72, 100 amu
68
Properties of Ekasilicon
69
Modern Periodic Table

• Moseley, Henry Gwyn Jeffreys
• 18871915, English physicist.
• Studied the relations among bright-line spectra
  of different elements.
• Derived the ATOMIC NUMBERS from the frequencies
  of vibration of X-rays emitted by each element.
• Moseley concluded that the atomic number is equal
  to the charge on the nucleus.
• This work explained discrepancies in Mendeleevs
  Periodic Law.

70
Modern Periodic Table

• the elements are arranged according to increasing
  atomic numbers

71
Periodic Table of the Elements
72
Organization of Periodic Table

• period - horizontal row
• group - vertical column

73
Family Names

• Group IA alkali metals
• Group IIA alkaline earth metals
• Group VIIA halogens
• Group VIIIA noble gases
• transition metals
• inner transition metals
• lanthanum series rare earths
• actinium series trans-uranium series

74
Types of Elements

• metals
• nonmetals
• metalloids - semimetals

75
Elements, Compounds, and Formulas

• Elements
• can exist as single atoms or molecules
• Compounds
• combination of two or more elements
• molecular formulas for molecular compounds
• empirical formulas for ionic compounds

76
Organic CompoundsOrganic Chemistry

• branch of chemistry in which carbon compounds and
  their reactions are studied.
• the chemistry of carbon-hydrogen compounds

77
Inorganic Compounds Inorganic Chemistry

• field of chemistry in which are studied the
  chemical reactions and properties of all the
  chemical elements and their compounds, with the
  exception of the hydrocarbons (compounds composed
  of carbon and hydrogen) and their derivatives.

78
Molecular and Structural Formulas
79
Bulk Substances

• mainly ionic compounds
• empirical formulas
• structural formulas

80
Models of Sodium Chloride
NaCl table salt
81
How many atoms are in the formula Al2(SO4)3? 3,
5, 17
82
Naming Binary Molecular Compounds

• For compounds composed of two non-metallic
  elements, the more metallic element is listed
  first.
• To designate the multiplicity of an element,
  Greek prefixes are used
• mono gt 1 di gt 2 tri gt 3 tetra gt 4 penta
  gt 5 hexa gt 6 hepta gt 7 octa gt 8

83
Common Compounds

• H2O
• water
• NH3
• ammonia
• N2O
• nitrous oxide
• CO
• carbon monoxide
• CS2
• carbon disulfide

• SO3
• sulfur trioxide
• CCl4
• carbon tetrachloride
• PCl5
• phosphorus pentachloride
• SF6
• sulfur hexafluoride

84
Alkanes - CnH2n2

• methane - CH4
• ethane - C2H6
• propane - C3H8
• butanes - C4H10
• pentanes - C5H12

• hexanes - C6H14
• heptanes - C7H16
• octanes - C8H18
• nonanes - C9H20
• decanes - C10H22

85
Burning of Propane Gas
86
Butanes
87
Ionic Bonding

• Characteristics of compounds with ionic bonding
• non-volatile, thus high melting points
• solids do not conduct electricity, but melts
  (liquid state) do
• many, but not all, are water soluble

88
Ion Formation
89
ValanceCharge on Ions

• compounds have electrical neutrality
• metals form positive monatomic ions
• non-metals form negative monatomic ions

90
Valence of Metal Ions

• Monatomic Ions
• Group IA gt 1
• Group IIA gt 2
• Maximum positive valence
• equals
• Group A

91
Valence of Non-Metal Ions

• Monatomic Ions
• Group VIA gt -2
• Group VIIA gt -1
• Maximum negative valence
• equals
• (8 - Group A )

92
Charges of Some Important Ions
93
Polyatomic Ions

• more than one atom joined together
• have negative charge except for NH4 and its
  relatives
• negative charges range from -1 to -4

94
Polyatomic Ions

• ammonium NH4
• perchlorate ClO41-
• cyanide CN1-
• hydroxide OH1-
• nitrate NO31-

• sulfate SO42-
• carbonate CO32-
• phosphate PO43-

95
Names of Ionic Compounds

• 1. Name the metal first.
• If the metal has more than one oxidation
  state, the oxidation state is specified by Roman
  numerals in parentheses.
• 2. Then name the non-metal,
• changing the ending of the non-metal to
• -ide.

96
Nomenclature

• NaCl
• sodium chloride
• Fe2O3
• iron(III) oxide
• N2O4
• dinitrogen tetroxide

• KI
• potassium iodide
• Mg3N2
• magnesium nitride
• SO3
• sulfur trioxide

97
Nomenclature

• NH4NO3
• ammonium nitrate
• KClO4
• potassium perchlorate
• CaCO3
• calcium carbonate
• NaOH
• sodium hydroxide

98
Nomenclature Drill

• Available for PCs
• on your disk to use at home or in the dorm
• in the Chemistry Resource Center
• off the web under Chapter 2, Links
  http//www.cbu.edu/mcondren/c115lkbk.html

99
How many moles of ions are there per mole of
Al2(SO4)3? 2, 3, 5
100
Chemical Equation

• reactants
• products
• coefficients
• reactants -----gt products

101
Writing and BalancingChemical Equations

• Write a word equation.
• Convert word equation into formula equation.
• Balance the formula equation by the use of
  prefixes (coefficients) to balance the number of
  each type of atom on the reactant and product
  sides of the equation.

102
Example

• Hydrogen gas reacts with oxygen gas to produce
  water.
• Step 1.
• hydrogen oxygen -----gt water
• Step 2.
• H2 O2 -----gt H2O
• Step 3.
• 2 H2 O2 -----gt 2 H2O

103
Example

• Iron(III) oxide reacts with carbon monoxide to
  produce the iron oxide (Fe3O4) and carbon
  dioxide.
• iron(III) oxide carbon monoxide -----gt Fe3O4
  carbon dioxide
• Fe2O3 CO -----gt Fe3O4 CO2
• 3 Fe2O3 CO -----gt 2 Fe3O4 CO2