Early Atomic Theory

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Early Atomic Theory

• Atoms, Molecules, and Ions

Preparation for College Chemistry Luis
Avila Columbia University Department of Chemistry
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Atoms
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Atomic Theory. Early Thoughts
EMPEDOCLES

• Matter is composed of four elements EARTH, AIR,
  WATER, FIRE

LEUCIPUS of Miletus and his disciple DEMOCRITUS
of Abdera

• Nature consists solely of an infinite number of
  indivisible particles, having shape, size,
  impenetrability, and no further properties.
  These particles move through an otherwise empty
  space.

• The shape, size, location, and movement of these
  particles make up literally all of the qualities,
  relations, and other features of the natural
  world.

PLATO and ARISTOTLE reinforces

• Matter is composed of four elements EARTH, AIR,
  WATER, FIRE

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GALILEO GALILEI

• Appearance of a new substance through chemical
  change involves
• rearrangement of parts too small to be seen.

FRANCIS BACON

• Heat might be a form of motion of small particles.

ROBERT BOYLE and ISAAC NEWTON

• Used atomic concepts to interpret physical
  phenomena.

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Daltons Model of the Atom
1. Elements consist of tiny particles called
atoms.
2. Atoms of the same element are alike in mass
and size.
3. Atoms of different elements differ in mass
and size.
4. Chemical compounds form by the union of two
or more atoms of different elements.
5. Atoms combine to form compounds in simple
numerical ratios, such as 12, 23, etc.
6. Atoms of two elements may combine in
different ratios to form more than one
compound.
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Consequences of Daltons Law
The Law of conservation of Mass
There is no detectable change in mass in an
ordinary chemical rxn.
The Law of Constant Composition
A compound always contains the same elements in
the same proportions by mass.
The Law of Multiple Proportions
The masses of one element that combine with a
fixed mass of the second element are in a ratio
of small whole numbers.
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Composition of Compounds
A compound always contains two or more elements
combined in a definite proportion by mass.
Atoms of two or more elements may combine in
different ratios to produce more than one
compound.
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Joseph Proust
Claude Berthollet
Proportions by mass of elements in a compound
VARY OVER A CERTAIN RANGE
Proportions by mass of elements in a compound ARE
FIXED. VARIATIONS ARE DUE TO IMPURITIES.
Careful experimentation lead Proust to
demonstrate
THE LAW OF DEFINITE PROPORTIONS (CONSTANT
COMPOSITION)
The proportions by mass of the elements in a
compound ARE FIXED, and do not depend on its mode
of preparation.
2HCl
H2 Cl2
2HCl Na2SO4
H2SO4 2NaCl
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Certain SOLIDS are exceptions of the Law of
Constant Composition NON STOICHIOMETRIC
COMPOUNDS (BERTHOLLIDES)
Wüstite, an iron oxide whose simplest formula is
FeO, with 77.73Fe.
Its composition truly ranges from Fe0.95O
(76.8 Fe) to Fe0.85O (74.8 Fe) depending of
the method of preparation.
All gaseous compounds OBEY THE LAW OF DEFINITE
PROPORTIONS.
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The composition of a compound is shown by its
CHEMICAL FORMULA.
CHEMICAL ANALYSIS
Lets take the elements C and O
(1.000 g C and 1.333 g O)
A
C O2
(1.000 g C and 2.667 g O)
B
C O2
1.333 2.667 or 1 2
For a FIXED mass of C the ratio of O in A and B
is

If A is CO2 then B is C2O4
If A is CO then B CO2
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We are unable to say which one is the right
formula, but we know the ratio C O is the
QUOTIENT OF INTEGERS.
CHEMICAL ANALYSIS
For Arsenic and Sulfur
A
(1.000 g As and 0.482 g S)
As S
(1.000 g As and 0.642 g S)
B
As S
0.482
2 3

For a FIXED mass of As the ratio of S in A and B
is

0.642
If A is As2S2 then B As2S3
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MICHAEL FARADAY
Certain substances when dissolved in water can
conduct an electric current.
SVANTE ARRHENIUS
Water is not necessary IONIC SUBSTANCES conduct
electricity when melted.
CATIONS POSITIVE IONS, they travel to the
CATHODE (negative electrode)
ANIONS NEGATIVE IONS that travel to the ANODE
(positive electrode).
G. J. STONEY
There must be some FUNDAMENTAL unit of
electricity associated with atoms ELECTRON.
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J.J Thomson Discovered the Electron
The first sub-atomic particle
Cathode rays are ELECTRONS (e-) particles with a
negative charge.
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The Nuclear Atom
"It was as though you had fired a fifteen-inch
shell at a piece of tissue paper and it had
bounced back and hit you."
ERNEST RUTHERFORD and HANS GEIGER with the
apparatus for counting alpha particles
Manchester, 1912
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The Nuclear Atom
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Arrangement of Subatomic Particles
Electron region
Nucleus
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Properties of Subatomic Particles
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Atomic Number, Z

• Equals number of protons in nucleus

• Equals number of electrons in neutral atom

• Location of the element in the Periodic Chart

• Characteristic of a particular element

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Mass Number, A
Atoms of the same element can differ in mass
number
A number of protons number of neutrons
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Nuclei Representation
A - Z number of neutrons
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Too heavy a-emission
For light (Z lt 20) isotopes the stable ratio is
1.0 with heavier isotopes it increases to 1.5.
There are no stable isotopes for elements of Z gt
83 (Bi).
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Precise determination of the masses of individual
atoms
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Meaning of Atomic Masses

• Give relative masses of atoms based on C12
  scale.
• The Most common isotope of carbon is assigned
  an atomic
• mass of 12 amu.
• The amu is defined as 1/12 of the mass of one
  neutral carbon
• atom

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Meaning of Atomic Masses
A nickel atom is 58.69 / 40.08 1.464 times as
heavy as a calcium ion It is 58.69 / 10.81
5.29 times as heavy as a boron ion
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Atomic Mass from Isotopic Composition
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Atomic Mass from Isotopic Composition
20.00 (0.9092)
21.00 (0.0026)
22.00 (0.0882)
20.18 amu
A.M. Ne 20.18g/mol
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Levels of Organization
Leptons
Quarks,...
http//www.rhic.bnl.gov/
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Molecules
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Composition
Held together by covalent bonds
Usually made up of nonmetal atoms
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Types of Formulas
CH3
Empirical
C2H6
Molecular
Structural
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Ions
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Formation of Monatomic Ions
Na atom (11p,11e -)
Na ion (11p,10e -) e -
F - ion (9p,10e -)
F atom (9p,9e -) e -
Nucleus remains unchanged
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Polyatomic Ions
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Polyatomic Ions
Anions
Cations
Permanganate
Ammonium
MnO4-
NH4
Peroxide
O22-
Mercury(I)
Hg22
Acetate
C2H3O2 -
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The prefixes and suffixes used to name oxyanions
are related to the valence of the element
contained in the formula
Hal -ate
Hal -ite
hypo-Hal -ite
per- Hal -ate
XO3-
XO-
XO2-
XO4-
Ex
Potassium Permanganate
KMnO4
KMnO3
Potassium Manganate
Ammonium hypochlorite
NH4ClO
(Hg2)(IO2)2
Mercury(I) iodite
Hg(BrO3)2
Mercury(II) bromate
Iron(III) periodate
Fe(IO4)3
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Writing Ionic Compound Formulas
Apply principle of electrical neutrality
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Ionic
Name cation followed by anion
For transition metals cations the charge is
indicated by Roman numeral when using the Stock
system
NH4Br ammonium bromide
Na2SO4 sodium sulfate
Fe(NO3)3 iron (III) nitrate
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Binary Molecular Compounds
Use of Greek prefixes
SF6 sodium hexafluoride
N2O3 dinitrogen trioxide
H2O dihydrogen monoxide
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Acids

• Binary Acids
• hydrochloric acid
• Oxoacids
• ate salt ic acid
• Examples
• HClO4 hyperchloric acid
• Ca(ClO4)2 calcium perchlorate

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Binary Compounds
Usually end in -ide
Metal/nonmetal
Hydrogen/nonmetal
Two nonmetals
not in water
in water
Metal with one type of cation
Metal with varying type of cations
prefix that indicate atoms for ea. element
1. prefix hydro- -suffix -ic 2. add word acid
Determine charge of cation
1. name metal 2. name nonmetal
1. Hydrogen 2. Name nonmetal
1. use roman numeral 2. stem name of nonmetal,
-ide
1. choose appropriate -ous or -ic ending on
metal 2. stem name of metal -ide