Chapter 3: Chemical Foundations

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Chapter 3 Chemical Foundations

• Elements, Atoms, and Ions

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The History of Chemistry

• Since ancient times, humans have used chemical
  changes
• Processing of ores to produce metals
• Embalming Fluids (prior to 1000 B.C.)
• The Greeks proposed (400 B.C.) that there were 4
  elements fire, earth, water and air.
• The next 2000 years were dominated by Alchemy
  which evolved into what we call Chemistry.
• Robert Boyle (1627-1691) proposed that science
  should based on repeatable experiments.

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History continued

• Boyle is best know for his work on the
  properties of gases.
• Defined the term element based on his
  experiments a substance was an element unless it
  could be broken down into two or more simpler
  substances.

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Elements Sec. 3.1Objectives 1) To learn about
the relative abundance of elements and the names
of elements.

• elements are pure substances
• organized by properties on periodic table
• each square shows the name and letter symbol for
  each element
• usually the symbols relate to the English names
  but some come from older names (usually Latin)
• Ex golds symbol is Au from aurum
• Ex irons symbol is Fe from ferrum

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The Elements

• Presently about 115 different elements are known.
• 88 occur naturally
• The remaining have been produced in the lab
• Only 9 elements account for most of the earths
  crust.

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Table 3.1
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Section 3.2 Symbols for Elements

• Objective
• To learn the symbols of some elements.

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Table 3.3
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Elemental Symbols

• Chemists use a set of abbreviations called
  Element Symbols.
• Rules
• Usually consist of the first letter of the first
  two letters of the element name.
• The first letter is always capitalized.

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Daltons Atomic TheorySection 3.3

• Objectives
• To learn about Daltons theory of atoms.
• To understand and illustrate the law of constant
  composition.

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Chemistry by the 18th Century

• Most natural materials are mixtures of pure
  substances.
• Pure substances are either elements or
  combinations of elements called compounds.
• Law of Constant Composition a given compound
  always has the same composition.

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John Dalton (1766-1844)

• English scientist and Teacher
• Meteorologist
• 1808 offered an explanation called Daltons
  Atomic Theory

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Daltons Atomic Theory

• Elements are made of tiny particles called atoms.
• All atoms of a given element are identical.
• The atoms of a given element are different from
  those of any other element.
• Atoms of one element can combine with atoms of
  other elements to form compounds. A given
  compound always has the relative numbers of
  atoms.
• Atoms are indivisible in chemical processes. That
  is, atoms are not created or destroyed in
  chemical reactions. A chemical reaction simply
  changes the way atoms are grouped together.

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The result
Dalton pictured compounds as collections of
atoms. Note that the number of atoms of each type
in a molecule is given by a subscript, except
that the number 1 is always assumed and not
written.
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Formulas of Compounds

• Section 3.4
• Objective
• To learn how a formula describes a compoundss
  composition.

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Chemical Formulas

• The types of atoms and the number of each type in
  each unit (molecule) of a given compound.
• Atoms are indicated by element symbols
• Number of each atom is indicated by subscript
• H2O

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Rules for Writing Formulas

• Each atom present is represented by a symbol.
• The number of each type of atom is indicated by a
  subscript written to the right of the symbol.
• When only one atom of a given type is present,
  the subscript 1 is not written.

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The Structure of the Atom

• Section 3.5
• Objectives
• To learn about the internal parts of an atom.
• To investigate Rutherfords experiment to
  characterize the atoms structure.

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Thomsons Experiment

• J.J. Thomson, physicist, showed in the late
  1890s showed that atoms had a negative charge
  because they were repelled by the negative part
  of an electric field.
• We now call these negative particles electrons.
• But he realized that the overall atom did not
  have a negative charge. Atoms must contain
  positive particles that balance the negative
  ones, giving the atom a zero charge.

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The Plum Pudding Model

• Lord Kelvin (a.k.a. William Thomson)
• Proposed that electrons were pictured as embedded
  in a positively charged spherical cloud, like
  raisins in plum pudding.

Plum Pudding Model
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Ernest Rutherford

• Ernest Rutherford (1871-1937)
• Nobel Prize in Chemistry in 1908
• 1911 Disproved Plum Pudding Model with his gold
  foil experiment.

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Figure 3.5 Rutherfords experiment.
Found that most particles passed through
indicating that most of the atom is empty space.
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Figure 3.6 Actual Results.
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How science changed

• Atoms have dense positive center (nucleus).
• Positive particles called Protons (1919).
• Neutral particle, Neutrons, found in 1932.
• Cathode Ray Tubes a stream of electrons passes
  between the electrodes (making neon signs, TV
  picture tubes and computer monitors possible).

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Modern Atomic Structure Isotopes

• Section 3.6-3.7
• Objectives
• To describe some important features of subatomic
  particles.
• To define the terms isotope, atomic number, and
  mass number.
• To use symbols to describe atoms.

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Visualizing an atom

• If the nucleus of an atom is the size of a grape
  then the electrons would be, on average, about
  one mile away.

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Terms

• Isotopes atoms with the same number of protons,
  but different numbers of neutrons.

Atomic Number The number of protons in the
nucleus of an atom.
Mass Number sum of the number of neutrons and
protons in a nucleus.
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Using Symbols for Isotopes
Z sum of protons neutrons A number of protons
Self Check p. 62
Find neutrons by subtracting atomic number from
the mass number.
Sodium-23 has how many neutrons?
23-1112 neutrons
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Periodic Table

• Section 3.8
• Objectives
• To describe the various features of the periodic
  table.
• To investigate some of the properties of metals,
  nonmetals, and metalloids.

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Periodic Table

• Groups
• also called families
• vertical columns
• numbered 1?18
• have similar chemical properties
• Periods
• horizontal rows
• properties change consistently across a period

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Periodic Table
Link to a fun periodic table.
A periodic table can be found inside the back
cover of your textbook.
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Periodic Table

• two rows below the periodic table are the
  lanthanide and actinide series
• these rows fit after 57 and 89
• they are only at the bottom to keep the width of
  the chart smaller

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Types of Elements

• Metals
• an element that is a good conductor of
  electricity
• at room temperature, most are solids
• malleable- can be rolled or hammered into sheets
• ductile- can be made into wire
• high tensile strength- can resist breakage when
  pulled
• most have silvery or grayish white luster

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Types of Elements

• Nonmetals
• an element that is a poor conductor of heat and
  electricity
• many are gases at room temperature
• some are solids usually brittle, not malleable

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Types of Elements

• Metalloids
• an element that has some characteristics of
  metals and nonmetals
• appear along staircase
• B, Si, Ge, As, Sb, Te
• all are solids at room temperature
• less malleable that metals but less brittle than
  nonmetals
• are semiconductors

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Types of Elements

• Noble Gases
• generally unreactive gases
• in far right column of periodic table

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Natural States of Elements

• Section 3.9
• Objectives
• To determine the natures of the common elements.

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Diatomic Molecules

• Molecules made up of two of the same atoms.
• 7 Diatomic moleucules HIBrONClF

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Allotropes

• Different forms of a given element.
• 3 allotropes of carbon

Diamond
Bucky Ball
Graphite
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Ions

• Section 3.10
• Objectives
• To describe the formation of ions from their
  parent atoms and name them.
• To predict which ion a given element forms by
  using the periodic table.

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Ions particles with a charge

• Cations positive ion, 1 or more electrons lost
• Anion negative ion, 1 or more electrons gained.
  Name by using root word and ide on the end.
  Chloride is Chlorine with one added electron.

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How do you know the charge?
Li
Be
B
C
2e-
6p
3p
4p
5p
1
IA
VIIA
VIIIA
3
2
IIA
IIIA
VIA
VA
IVA
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N
O
F
Ne
Na
8e-
2e-
8p
10p
7p
9p
11p
-1
0
1
4
IA
VIIA
VIIIA
-3
-2
-4
3
2
IIA
IIIA
VIA
VA
IVA
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Figure 3.19 The ions formed by selected members
of groups 1, 2, 3, 6, and 7.
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Compounds that Contain Ions

• Section 3.11
• Objectives
• To describe how ions combine to form neutral
  compounds.

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Ionic Compounds

• High melting points
• Conduct electric current when melted or dissolved
  in water.
• Formed by a metal Cation and a nonmetal Anion.
• Has a net charge of Zero!

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-1
2
F
Be
2e-
2e-
4p
9p
-1
0
1
4
IA
VIIA
VIIIA
-3
-4
-2
3
2
IIA
IIIA
VIA
VA
IVA
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-1
0
1
4
IA
VIIA
VIIIA
-3
-4
-2
3
2
IIA
IIIA
VIA
VA
IVA
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Berylium Fluoride
BeF2
-1
0
1
4
IA
VIIA
VIIIA
-3
-4
-2
3
2
IIA
IIIA
VIA
VA
IVA
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For ionic compounds with a metal from group 1A,
2A, 3A place the metal first and name it
first. The non-metal is put last and named last.
The number of metals or non-metals is depends on
how many it takes to balance the charges.
-1
1
IA
VIIA
VIIIA
-3
-2
2
IIA
IIIA
VIA
VA
IVA
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Writing formulas for Ionic Compounds

• When metals combine with nonmetals they do so by
  forming ions
• To write the formula for the compound
• 1. Identify the potential charge for each
  element.
• 2. Write the cation first, and then the
  anion.
• 3. Use the criss-cross method.
• 4. Reduce the subscripts to the lowest
  common factor.

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• Example.
• When Magnesium (Mg) combines with chlorine (Cl)
• Mg is in group 2 and has a valence of 2
• Cl is in group 7 and has a valence of -1.
• Mg2 Cl-1 MgCl2