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Chemistry Chapter 3

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Title: Chemistry Chapter 3


1
Chemistry Chapter 3
Chemical Foundations Elements, Atoms, and Ions
2
Top Ten
3
Table 3.1
4
Table 3.3
5
History of Chemistry
  • 400 B.C. Greeks proposed 4 elements
  • Earth
  • Fire
  • Water
  • Air
  • Next 2000 yearsalchemy
  • During this period discoveries were made
  • Hg, S, Sb
  • prepared acids

6
Controversial Thinking!
Democritus (460-370 B.C)
Greek thinker Coined the term atoms and thought
they were indivisible.
Aristotle (384 B.C.-322B.C.)
Thought matter was continuous and indefinitely
divisible (did not believe in atoms) His idea
was accepted for nearly 2000 years!
7
Indivisible or Divisible?Democritis vs. Aristotle
8
Robert Boyle
  • Founder of Modern Chemistry (1627-1691)
  • Took the Al out of Alchemy (although he started
    as one)
  • First scientist to understand the importance of
    careful measurement
  • Insisted science be based on experiments
  • Famous for P1/V

9
Late 1700s
  • Most chemists accepted element definition
  • Understood elements combined to form compounds
    with various properties
  • Disagreed whether compounds are always in the
    same ratio

10
What happened in 1790?
  • Study of matter was revolutionized by new
    emphasis on Quantitative Analysis
  • Aided by improved balances
  • Measurements were actually ACCURATE!!!

11
Antoine Lavoisier
  • Father of Modern Chemistry (1743-1794)
  • Recognized and named hydrogen and oxygen
  • Introduced the metric system
  • Wrote first list of elements and revised
    nomenclature
  • Because of prominence in pre-revolutionary
    government, was beheaded at the height of the
    French revolution

12
Law of Conservation of Mass
Mass is neither created nor destroyed during
chemical or physical reactions.
Total mass of reactants Total mass of products
Antoine Lavoisier
13
Law of Definite (or Constant) Composition
  • The fact that a chemical compound contains the
    same elements in exactly the same proportions by
    mass regardless of the size of the sample or the
    source of the compound.

14
What does this mean? (Law of Definite Composition)
  • 50.0 g sample of pure H2O decomposed into its
    elements
  • would find 5.6 g H and 44.4 g oxygen
  • mass would be
  • mass H 5.60 g x 100 11.2 H
  • total mass 50.0 g
  • mass 0 44.4 g x 100 88.8 O
  • total mass 50.0 g

15
Law of Multiple Proportions
  • If two or more different compounds are composed
    of the same two elements, then the ratio of the
    masses of the second element combined with a
    certain mass of the first element is always a
    ratio of small whole numbers. (CO, CO2)

16
Figure 3.2 Representation of NO, NO2, and N2O.
17
John DaltonBeginning of Modern Atomic Theory
  • Englishman from a Quaker family (1766-1844)
  • Revolutionized chemistry by emphasizing that
    atoms can have weights and weights can be
    measured (quantitative)
  • Opened a school at age 12
  • Color blind/researched
  • Interested in botany
  • Theory not accepted until 1905 Albert Einstein
    paper

18
Daltons Atomic Theory (1808)
  • All matter is composed of extremely small
    particles called atoms (fundamental particles)
  • Atoms of a given element are identical.

John Dalton
  • Atoms cannot be subdivided, created, or
    destroyed.
  • Atoms of different elements combine in simple
    whole-number ratios to form chemical compounds.
    (Law of Multiple Proportions)
  • In chemical reactions, atoms are combined,
    separated, or rearranged

19
Dalton vs. Today
All matter is composed of extremely small particles called atoms. (fundamental particles) Atoms are not fundamental, made up of smaller particles (protons, neutrons, electrons)
Atoms of a given element are identical. Atoms of a given element have same p and e-, but may differ in of neutrons.
Atoms cannot be subdivided, created, or destroyed. except in nuclear chemistry
Law of Multiple Proportions Law of Multiple Proportions
In chemical reactions, atoms are combined, separated, or rearranged In chemical reactions, atoms are combined, separated, or rearranged
20
  • What does an atom look like?
  • (Sketch it on your paper!)

21
This is The Modern Atomic Model
22
Atomic Particles
Particle Charge Mass (kg) Location
Electron (e-) (J.J.Thomson 1897) -1 9.109 x 10-31 Electron cloud
Proton (p) (Thomson/Goldstein/ Rutherford 1907-1919) 1 1.673 x 10-27 Nucleus
Neutron (no) (Chadwick 1932) 0 1.675 x 10-27 Nucleus
23
Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube to
deduce the presence of a negatively charged
particle.
Cathode ray tubes pass electricity through a gas
that is contained at a very low pressure.
24
Figure 3.7 Schematic of a cathode ray tube.
25
Some ModernCathode Ray Tubes
26
Mass of the Electron
1909 Robert Millikan determines the mass of the
electron.
The oil drop apparatus
Mass of the electron is 9.109 x 10-31 kg
27
Conclusions from the Study of the Electron
  • Cathode rays have identical properties
    regardless of the element used to produce them.
    All elements must contain identically charged
    electrons.
  • Atoms are neutral, so there must be positive
    particles in the atom to balance the negative
    charge of the electrons
  • Electrons have so little mass that atoms must
    contain other particles that account for most of
    the mass

28
Thomsons Atomic Model
Thomson believed that the electrons were like
plums embedded in a positively charged pudding,
thus it was called the plum pudding
model. Based on the following facts (1) atoms
contain small, negatively charged particles
called electrons and (2) the atoms of the element
behave as if they have no charge at all
29
Ernest Rutherford
  • 1871-1937
  • Learned physics in JJ Thomsons lab
  • Did much work with alpha particles ( charged
    part with mass)
  • Most famous for his GOLD FOIL EXPERIMENT

30
Figure 3.5 Rutherfords experiment.
31
Try it Yourself!
In the following pictures, there is a target
hidden by a cloud. To figure out the shape of the
target, we shot some beams into the cloud and
recorded where the beams came out. Can you figure
out the shape of the target?
32
The Answers
Target 1
Target 2
33
Figure 3.3 Plum Pudding model of an atom.
34
Figure 3.6 Results of foil experiment if Plum
Pudding model had been correct.
35
Figure 3.6 Actual results.
36
Rutherfords Findings
  • Most of the particles passed right through
  • A few particles were deflected
  • VERY FEW were greatly deflected

Like howitzer shells bouncing off of tissue
paper!
Conclusions
  • The nucleus is small
  • The nucleus is dense
  • The nucleus is positively charged

37
Disbelievers.
  • Albert Einstein when to his grave not totally
    believing it
  • According to classical physics, the electron
    would have collapsed into the nucleus
  • 1910-1930 began the Quantum Physics Revolution
    (the physics of atomic and subatomic particles)

38
The Atomic Scale
  • Most of the mass of the atom is in the nucleus
    (protons and neutrons)
  • Electrons are found outside of the nucleus (the
    electron cloud)
  • Most of the volume of the atom is empty space

q is a particle called a quark
39
The Quark
Oopswrong Quark!
40
About Quarks
Protons and neutrons are NOT fundamental
particles.
Protons are made of two up quarks and one
down quark.
Neutrons are made of one up quark and two
down quarks.
Quarks are held together by gluons
41
Figure 3.9 A nuclear atom viewed in cross
section.
42
Atomic Number
Atomic number (Z) of an element is the number of
protons in the nucleus of each atom of that
element.
Element of protons Atomic (Z)
Carbon 6 6
Phosphorus 15 15
Gold 79 79
43
(No Transcript)
44
Isotopes
Elements occur in nature as mixtures of isotopes.
Isotopes are atoms of the same element that
differ in the number of neutrons
45
Figure 3.10 Two isotopes of sodium.
46
Mass Number
Mass number is the number of protons and neutrons
in the nucleus of an isotope.
Mass p n0
Nuclide p n0 e- Mass
Oxygen - 10
- 33 42
- 31 15
8
8
18
18
Arsenic
75
33
75
Phosphorus
15
31
16
47
Atomic Masses
Atomic mass is the average of all the naturally
isotopes of that element.
Carbon 12.011
Isotope Symbol Composition of the nucleus in nature
Carbon-12 12C 6 protons 6 neutrons 98.89
Carbon-13 13C 6 protons 7 neutrons 1.11
Carbon-14 14C 6 protons 8 neutrons lt0.01
48
IsotopesAgain (must be on the test)
Isotopes are atoms of the same element having
different masses due to varying numbers of
neutrons.
Isotope Protons Electrons Neutrons Nucleus
Hydrogen1 (protium) 1 1 0
Hydrogen-2 (deuterium) 1 1 1
Hydrogen-3 (tritium) 1 1 2
49
Chlorine Practice Problem
  • Chlorine exists as 2 isotopes in nature. Cl-35
    (atomic mass 34.969 amu) has a 75.77 relative
    abundance. Cl-37 has an atomic mass 36.966 amu.
  • What is the abundance of the Cl-37 isotope?

50
Chlorine Practice Problem
  • Chlorine exists as 2 isotopes in nature. Cl-35
    (atomic mass 34.969 amu) has a 75.77 relative
    abundance. Cl-37 has an atomic mass 36.966 amu
  • Calculate the atomic mass of Chlorine.

51
Chlorine Practice Problem
  • Chlorine exists as 2 isotopes in nature. Cl-35
    (atomic mass 34.969 amu) has a 75.77 relative
    abundance. Cl-37 has an atomic mass 36.966 amu.
  • How many times more massive is Cl-37 than Cl-35?

52
Atomic and Atomic Mass
  • The Periodic Law

53
Chinese Periodic Table
54
Triangular Periodic Table
55
Mayan Periodic Table
56
Stowe Periodic Table
57
A Spiral Periodic Table
58
Modern Russian Table
59
The Year 1860.
  • First International Congress of Chemists
  • 60 to 70 of 113 elements had been discovered
  • Italian chemist Cannizzaro presented method for
    measurement of atomic mass that all could agree
    on.

60
Dimitri Mendeeleev
  • Writing a book about the same time.
  • Wanted to include new information of atomic
    masses
  • Wanted to find an arrangement for all of the
    information on the 60-70 elements

61
Law of Mendeleev
  • Properties of the elements recur in regular
    cycles (periodically) when the elements are
    arranged in order of increasing atomic mass.

62
Missing?
14 Si 28.09
??
50 Sn 118.71
Named missing element Ekasilicon
From base word eka meanging next in order
63
Ekasilicon
Predicted Properties Observed Properties
Atomic Mass 72 amu
Density 5.5 g/cm3
Melting Point 825 C
64
Ekasilicon
Predicted Properties Observed Properties
Atomic Mass 72 amu 72.61 amu
Density 5.5 g/cm3 5.32 g/cm3
Melting Point 825 C 938 C
65
Ekasilicon
Predicted Properties Observed Properties
Oxide Formula XO2 GeO2

Chloride Formula XCl4 GeCl4
66
Mendeleevs Periodic Table
Dmitri Mendeleev
67
Figure 3.11 The periodic table
68
Figure 3.11 The periodic table
69
Periodic Table with Group Names
70
The Periodic Table
Period
Group or Family
Group or family
Period
71
Periodic Table with Group Names
72
Figure 3.12 Elements classified as metals and
nonmetals.
73
Properties of Metals
  • Metals are good conductors of heat and
    electricity
  • Metals are malleable
  • Metals are ductile
  • Metals have high tensile strength
  • Metals have luster

74
Figure 3.17 Spherical atoms packed closely
together.
75
Metalloids
  • Mostly brittle solids
  • Properties between metal and non-metal
    (semi-conductors)
  • With exception of Bismuth, found in nature only
    as compound
  • Once obtained as free metals, that are stable in
    the presence of air

76
Properties of Nonmetals
Carbon, the graphite in pencil lead is a great
example of a nonmetallic element.
  • Nonmetals are poor conductors of heat and
  • electricity
  • Nonmetals tend to be brittle
  • Many nonmetals are gases at room temperature

77
Examples of Nonmetals
Microspheres of phosphorus, P, a reactive
nonmetal
Sulfur, S, was once known as brimstone
Graphite is not the only pure form of carbon, C.
Diamond is also carbon the color comes from
impurities caught within the crystal structure
78
Figure 3.14 Nitrogen gas contains N2 molecules.
79
Figure 3.13 A collection of argon atoms.
80
Figure 3.14 Oxygen gas contains O2 molecules.
81
Table 3.5
82
Allotropes
  • Different forms of a given element
  • Different properties b/c different arrangement of
    atoms
  • EX diamond, graphite, Buckminsterfullerene (All
    Carbon!)
  • Look in your bookp. 70

83
TYPES OF IONS (Remember an ion is an atom or
group of atoms that has a net or net charge.
Cations
  • Positively charged ions
  • Smaller than the corresponding
  • atom (lost e/closer together)

Anions
  • Negatively charged ions
  • Larger than the corresponding
  • atom (gained e/spread apart

84
Table of Ion Sizes
85
Figure 3.11 The periodic table
86
Figure 3.19 The ions formed by selected members
of groups 1, 2, 3, 6, and 7.
87
Figure 3.20 Pure water does not conduct a
current.
88
Figure 3.20 Water containing dissolved salt
conducts a current.
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