Chapter 2 Atoms, Molecules, and Ions

1
Chapter 2Atoms, Molecules, and Ions
2

• Important Read Before Using Slides in Class
• Instructor This PowerPoint presentation contains
  photos and figures from the text, as well as
  selected animations and videos. For animations
  and videos to run properly, we recommend that you
  run this PowerPoint presentation from the
  PowerLecture disc inserted in your computer.
  Also, for the mathematical symbols to display
  properly, you must install the supplied font
  called Symb_chm, supplied as a cross-platform
  TrueType font in the Font_for_Lectures folder
  in the "Media" folder on this disc.
• If you prefer to customize the presentation or
  run it without the PowerLecture disc inserted,
  the animations and videos will only run properly
  if you also copy the associated animation and
  video files for each chapter onto your computer.
  Follow these steps
• 1. Go to the disc drive directory containing the
  PowerLecture disc, and then to the Media
  folder, and then to the PowerPoint_Lectures
  folder.
• 2. In the PowerPoint_Lectures folder, copy the
  entire chapter folder to your computer.
  Chapter folders are named chapter1,
  chapter2, etc. Each chapter folder contains
  the PowerPoint Lecture file as well as the
  animation and video files.
• For assistance with installing the fonts or
  copying the animations and video files, please
  visit our Technical Support at http//academic.cen
  gage.com/support or call [phone]. Thank
  you.

3
ATOMS, Molecules, Ions
4
ATOMIC COMPOSITION

• Protons
• electrical charge
• mass 1.672623 x 10-24 g
• relative mass 1.007 atomic mass units
  (u)
• Electrons
• negative electrical charge
• relative mass 0.0005 u
• Neutrons
• no electrical charge
• mass 1.009 u

5
ATOM COMPOSITION
The atom is mostly empty space

• protons and neutrons in the nucleus.
• the number of electrons is equal to the number of
  protons.
• electrons in space around the nucleus.
• extremely small. One teaspoon of water has 3
  times as many atoms as the Atlantic Ocean has
  teaspoons of water.

PLAY MOVIE
6
Atomic Number, Z

• All atoms of the same element have the same
  number of protons in the nucleus, Z

13
Al
26.981
7
Atomic Weight

• This tells us the mass of one atom of an element
  relative to one atom of another element.
• OR the mass of 1000 atoms of one relative to
  1000 atoms of another.
• For example, an O atom is approximately 16 times
  heavier than an H atom.
• Define one element as the standard against which
  all others are measured
• Standard carbon

8
Mass Number, A

• C atom with 6 protons and 6 neutrons is the mass
  standard
• 12 atomic mass units (u)
• Mass Number (A) protons neutrons
• A boron atom can have A 5 p 5 n
  10 u

9
Boron in Death Valley

• Death Valley has been a major source of borax and
  other boron-containing minerals.
• Borax was transported out of Death Valley in
  wagons pulled by teams of 20 mules.

10
Isotopes

• Atoms of the same element (same Z) but different
  mass number (A).
• Boron-10 has 5 p and 5 n 105B
• Boron-11 has 5 p and 6 n 115B

11
Hydrogen Isotopes
Hydrogen has _____ isotopes
1 proton and 0 neutrons, protium
11H
1 proton and 1 neutron, deuterium
21H
1 proton and 2 neutrons, tritium radioactive
31H
12
Isotope Composition

13
Isotopes Their Uses
Heart scans with radioactive technetium-99.
9943Tc Emits gamma rays
14
Masses of Isotopesdetermined with a mass
spectrometer
See Active Figure 2.3
15
Mass spectrum of C6H5Br
16
Isotopes

• Because of the existence of isotopes, the mass of
  a collection of atoms has an average value.
• Average mass ATOMIC WEIGHT
• Boron is 19.9 10B and 80.1 11B. That is, 11B
  is 80.1 percent abundant on earth.
• For boron atomic weight
• 0.199 (10.0 u) 0.801 (11.0 u) 10.8 u

17
Isotopes Atomic Weight

• Because of the existence of isotopes, the mass of
  a collection of atoms has an average value.
• 6Li 7.5 abundant and 7Li 92.5
• Atomic weight of Li ______________
• 28Si 92.23, 29Si 4.67, 30Si 3.10
• Atomic weight of Si ______________

18
Periodic Table

• Dmitri Mendeleev (1834-1907) developed the modern
  periodic table. Argued that element properties
  are periodic functions of their atomic weights.
• We now know that element properties are periodic
  functions of their ATOMIC NUMBERS.

19
Periods in the Periodic Table
PLAY MOVIE
20
Groups/Families in the Periodic Table
PLAY MOVIE
21
Regions of the Periodic Table
22
Element Abundance
C
O
Al
Si
Fe
http//www.webelements.com/
23
Hydrogen
PLAY MOVIE

• Shuttle main engines use H2 and O2

24
Group 1A Alkali MetalsLi, Na, K, Rb, Cs
PLAY MOVIE
Reaction of potassium H2O
Cutting sodium metal
25
Group 2A Alkaline Earth Metals Be, Mg, Ca, Sr,
Ba, Ra
Magnesium
Magnesium oxide
PLAY MOVIE
26
Group 3A B, Al, Ga, In, Tl
Cu
Al
Al resists corrosion (here in nitric acid).
Gallium is one of the few metals that can be
liquid at room temp.
27
Gems Minerals

• Sapphire Al2O3 with Fe3 or Ti3 impurity gives
  blue whereas V3 gives violet.
• Ruby Al2O3 with Cr3 impurity

28
Group 4A C, Si, Ge, Sn, Pb
Quartz, SiO2
Diamond
29
Group 5A N, P, As, Sb, Bi
PLAY MOVIE
Ammonia, NH3

• White and red phosphorus

30
Phosphorus

• Phosphorus first isolated by Brandt from urine,
  1669

31
Group 6A O, S, Se, Te, Po

• Sulfuric acid dripping from snot-tite in cave in
  Mexico

Elemental S has a ring structure.
32
Group 7A HalogensF, Cl, Br, I, At
PLAY MOVIE
33
Group 8A Noble Gases He, Ne, Ar, Kr, Xe, Rn
34
Transition Elements

• Lanthanides and actinides

Iron in air gives iron(III) oxide
35
Colors of Transition Metal Compounds
Iron
Cobalt
Nickel
Copper
Zinc
36
Molecules, Ions Their Compounds
PLAY MOVIE
Ethanol, C2H6O
Buckyball, C60
37
Compounds Molecules

• COMPOUNDS are a combination of 2 or more elements
  in definite ratios by mass.
• The character of each element is lost when
  forming a compound.
• MOLECULES are the smallest unit of a compound
  that retains the characteristics of the compound.

38
MOLECULAR FORMULAS

• Formula for glycine is C2H5NO2
• In one molecule there are
• 2 C atoms
• 5 H atoms
• 1 N atom
• 2 O atoms

39
WRITING FORMULAS

• Can also write glycine formula as
• H2NCH2COOH to show atom ordering
• or in the form of a structural formula

40
MOLECULAR MODELING
Structural formula of glycine
Ball stick
Space-filling
41
Molecular Ionic Compounds
Fe
N
Iron-porphyrin
NaCl
42
ELEMENTS THAT EXIST AS MOLECULES
Allotropes of C
43
ELEMENTS THAT EXIST AS DIATOMIC MOLECULES
44
ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES
S8 sulfur molecules
White P4 and polymeric red phosphorus
45
IONS AND IONIC COMPOUNDS
46
IONS AND IONIC COMPOUNDS

• IONS are atoms or groups of atoms with a positive
  or negative charge.
• Taking away an electron from an atom gives a
  CATION with a positive charge
• Adding an electron to an atom gives an ANION with
  a negative charge.

47
Forming Cations Anions
A CATION forms when an atom loses one or more
electrons.
An ANION forms when an atom gains one or more
electrons
PLAY MOVIE
PLAY MOVIE
F e- f F-
Mg f Mg2 2 e-
48
See Active Figure 2.17
49
PREDICTING ION CHARGES
See Figure 2.18

• In general
• metals (Mg) lose electrons f cations
• nonmetals (F) gain electrons f anions

50
Charges on Common Ions
3
By losing or gaining e-, atom has same number of
e-s as nearest Group 8A atom.
51
Predicting Charges on Monatomic Ions
52
METALS

• M f n e- Mn
• where n periodic group
• Na sodium ion
• Mg2 magnesium ion
• Al3 aluminum ion
• Transition metals f M2 or M3 are common
• Fe2 iron(II) ion
• Fe3 iron(III) ion

53
NONMETALS

• NONMETAL n e- f Xn- where n 8 - Group
  no.

N3-, nitride
O2-, oxide
F-, fluoride
S2-, sulfide
Cl-, chloride
Name derived by adding -ide to stem
Br-, bromide
I-, iodide
54
Ion Formation

• Reaction of aluminum and bromine

PLAY MOVIE
55
POLYATOMIC IONS

• Groups of atoms with a charge.
• MEMORIZE the names and formulas in Table 2.4,
  page 74.

Celestite, SrSO4
56
Note many O containing anions have names ending
in ate (or -ite).
57
Polyatomic Ions
NO3- nitrate ion
HNO3 nitric acid
58
Polyatomic Ions

• NH4
• ammonium ion
• One of the few common polyatomic cations

59
Polyatomic Ions

• CO32-
• carbonate ion
• HCO3-
• bicarbonate ion
• hydrogen carbonate

60
Polyatomic Ions

• PO43-
• phosphate ion
• CH3CO2-
• acetate ion

61
Polyatomic Ions

• SO42-
• sulfate ion
• SO32-
• sulfite ion

62
Polyatomic Ions

• NO3-
• nitrate ion
• NO2-
• nitrite ion

63
COMPOUNDS FORMED FROM IONS
CATION ANION f COMPOUND

• Na Cl- f NaCl

A neutral compd. requires equal number of
and - charges.
64
IONIC COMPOUNDS
ammonium chloride, NH4Cl
65
Some Ionic Compounds
Ca2 2 F- f
CaF2

• Mg2 NO3- f
• Mg(NO3)2
• magnesium nitrate
• Fe2 PO43- f
• Fe3(PO4)2
• iron(II) phosphate
• Be sure to practice naming compounds.

calcium fluoride
66
Properties of Ionic CompoundsForming NaCl from
Na and Cl2

• A metal atom can transfer an electron to a
  nonmetal.
• The resulting cation and anion are attracted to
  each other by electrostatic forces.

PLAY MOVIE
PLAY MOVIE
67
Electrostatic Forces
PLAY MOVIE

• The oppositely charged ions in ionic compounds
  are attracted to one another by ELECTROSTATIC
  FORCES.
• These forces are governed by COULOMBS LAW.

68
Electrostatic Forces

• COULOMBS LAW

As ion charge increases, the attractive force
_______________. As the distance between ions
increases, the attractive force
________________. This idea is important and will
come up many times in future discussions!
69
Electrostatic Forces

• COULOMBS LAW

See Active Figure 2.21
70
Importance of Coulombs Law
NaCl, Na and Cl-, m.p. 804 oC
MgO, Mg2 and O2- m.p. 2800 oC
71
Molecular CompoundsCompounds without Ions
CO2 Carbon dioxide
PLAY MOVIE
BCl3 boron trichloride
CH4 methane
72
Naming Molecular Compounds
All are formed from two or more nonmetals.
CO2 Carbon dioxide
Ionic compounds generally involve a metal and
nonmetal (NaCl)
PLAY MOVIE
BCl3 boron trichloride
CH4 methane
73
Counting Atoms

• Mg burns in air (O2) to produce white magnesium
  oxide, MgO.

How can we figure out how much oxide is produced
from a given mass of Mg?
PLAY MOVIE
74
Counting Atoms

• Chemistry is a quantitative sciencewe need a
  counting unit.

MOLE
1 mole is the amount of substance that contains
as many particles (atoms, molecules) as there are
in 12.0 g of 12C.
518 g of Pb, 2.50 mol
75
Particles in a Mole
Avogadros Number
Amedeo Avogadro 1776-1856

• 6.0221415 x 1023

There is Avogadros number of particles in a mole
of any substance.
76
Molar Mass

• 1 mol of 12C 12.00 g of C 6.022 x 1023
  atoms of C
• 12.00 g of 12C is its MOLAR MASS
• Taking into account all of the isotopes of C, the
  molar mass of C is 12.011 g/mol

77
One-mole Amounts
78
PROBLEM What amount of Mg is represented by
0.200 g? How many atoms?

• Mg has a molar mass of 24.3050 g/mol.

How many atoms in this piece of Mg?
4.95 x 1021 atoms Mg
79
MOLECULAR WEIGHT AND MOLAR MASS

• Molecular weight sum of the atomic weights of
  all atoms in the molecule.
• Molar mass molecular weight in grams

80
What is the molar mass of ethanol, C2H6O?

• 1 mol contains
• 2 mol C (12.01 g C/1 mol) 24.02 g C
• 6 mol H (1.01 g H/1 mol) 6.06 g H
• 1 mol O (16.00 g O/1 mol) 16.00 g O
• TOTAL molar mass 46.08 g/mol

81
Tylenol

• Formula
• Molar mass

C8H9NO2
151.2 g/mol
82
Molar Mass
83
Empirical Molecular Formulas

• A pure compound always consists of the same
  elements combined in the same proportions by
  weight.
• Therefore, we can express molecular composition
  as PERCENT BY WEIGHT

Ethanol, C2H6O 52.13 C 13.15 H 34.72 O
84
Percent Composition

• Consider some of the family of nitrogen-oxygen
  compounds
• NO2, nitrogen dioxide and closely related, NO,
  nitrogen monoxide (or nitric oxide)

Chemistry of NO, nitrogen monoxide
PLAY MOVIE
85
Percent Composition

• Consider NO2, Molar mass ?
• What is the weight percent of N and of O?

What are the weight percentages of N and O in NO?
86
How to Determine a Formula?

• Mass spectrometer

87
Mass Spectrum of Ethanol
88
Determining Formulas

• In chemical analysis we determine the by weight
  of each element in a given amount of pure
  compound and derive the EMPIRICAL or SIMPLEST
  formula.
• PROBLEM A compound of B and H is 81.10 B.
  What is its empirical formula?

89
A compound of B and H is 81.10 B. What is its
empirical formula?

• Because it contains only B and H, it must contain
  18.90 H.
• In 100.0 g of the compound there are 81.10 g of B
  and 18.90 g of H.
• Calculate the number of moles of each constituent.

90
A compound of B and H is 81.10 B. What is its
empirical formula?

• Calculate the number of moles of each element in
  100.0 g of sample.

91
A compound of B and H is 81.10 B. What is its
empirical formula?

• Now, recognize that atoms combine in the ratio of
  small whole numbers.
• 1 atom B 3 atoms H f 1 molecule BH3
• or
• 1 mol B atoms 3 mol H atoms f 1 mol BH3
  molecules
• Find the ratio of moles of elements in the
  compound.

92
A compound of B and H is 81.10 B. What is its
empirical formula?
Take the ratio of moles of B and H.
Always divide by the smaller number.

• But we need a whole number ratio.
• 2.5 mol H/1.0 mol B 5 mol H to 2 mol B
• EMPIRICAL FORMULA B2H5

93
A compound of B and H is 81.10 B. Its empirical
formula is B2H5. What is its molecular formula?

• Is the molecular formula B2H5, B4H10, B6H15,
  B8H20, etc.?

94
A compound of B and H is 81.10 B. Its
empirical formula is B2H5. What is its molecular
formula?

• We need to do an EXPERIMENT to find the MOLAR
  MASS.
• Here experiment gives 53.3 g/mol
• Compare with the mass of B2H5
• 26.66 g/unit
• Find the ratio of these masses.

Molecular formula B4H10
95
DETERMINE THE FORMULA OF A COMPOUND OF Sn AND I
Sn(s) some I2(s) f SnIx
96
Data to Determine the formula of a SnI Compound

• Reaction of Sn and I2 is done using excess Sn.
• Mass of Sn in the beginning 1.056 g
• Mass of iodine (I2) used 1.947 g
• Mass of Sn remaining 0.601 g
• See p. 93

97
Tin and Iodine Compound

• Find the mass of Sn that combined with 1.947 g
  I2.
• Mass of Sn initially 1.056 g
• Mass of Sn recovered 0.601 g
• Mass of Sn used 0.455 g
• Find moles of Sn used

98
Tin and Iodine Compound

• Now find the number of moles of I2 that combined
  with 3.83 x 10-3 mol Sn. Mass of I2 used was
  1.947 g.

How many mol of iodine atoms?
1.534 x 10-2 mol I atoms
99
Tin and Iodine Compound

• Now find the ratio of number of moles of moles of
  I and Sn that combined.

Empirical formula is SnI4