Download Atoms, Molecules, and Ions (2)

8/31/08
2.1 The Early History of Chemistry
Atoms, Molecules, and Ions
 It all started with the Greeks. (400 B.C.)
Chapter 2
 Demokritos theorized atomos = indivisible
particles.
 Alchemy dominated for 2000 years.
 2.2 Fundamental Chemical Laws
2.1 The Early History of Chemistry
 Systematic metallurgy is the foundation of
modern chemistry. (1500’s)
 Extraction of metals from ore.
 Robert Boyle (1627-1691)
   Antoine Lavoisier (1743-1794)
“Father of Modern Chemistry”
Explained the true nature of combustion
 Verified the law of conservation of mass
  First to perform truly quantitative experiments.
“Boyles Law” pressure v. volume
2.2 Fundamental Chemical Laws
 Joseph Proust (1754-1826)
 Law of definite proportion
given compound always contains the same
proportion of elements by mass
2.3 Dalton’s Atomic Theory
 John Dalton (1766-1844)
 Four Postulates (1808)
 Prepared the first table of atomic masses
 A
 John Dalton (1766-1844)
 “Psuedoscience” that tried to turn common
metals into gold.
 We
will get back to these later.
 Many
values later proven wrong.
Law of multiple proportions (see p. 43)
 Dalton
could not determine absolute chemical
formulas.
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2.3 Dalton’s Atomic Theory
 Dalton’s Four Postulates (see p. 45)
Each element is made up of tiny particles called
atoms.
 The atoms of a given element are identical; the
atoms of different elements are different in some
fundamental way(s).
 2.3 Dalton’s Atomic Theory
2.3 Dalton’s Atomic Theory
 Dalton’s Four Postulates
Chemical compounds are formed when atoms of
different elements combine with each other. A
given chemical compound always has the same
relative numbers and types of atoms.
 Chemical reactions involve reorganization of
atoms—changes in the way they are bound
together. The atoms themselves remain
unchanged.
 2.3 Dalton’s Atomic Theory
 Joseph Gay-Lussac (1778-1850)
 Performed experiments combining measured
volumes of gases at constant temperature and
pressure.
2.3 Dalton’s Atomic Theory
Avogadro’s Hypothesis
 Avagadro’s Hypothesis (1811)
 At the same temperature and pressure, equal
volumes of different gases contain the same
number of particles.
 The
volume of a gas is determined by the number of
molecules present not the size of the individual
particles.
Figure 2.5
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2.4 Early Atomic Experiments
2.4 Early Atomic Experiments
 J.J. Thomson (1856-1940)
 Used cathode-ray tubes
 When
electricity is applied to the tube a “ray” is
emitted from the cathode
Figure 2.7
2.4 Early Atomic Experiments
 Thomson noted the ray was repelled by a
negative electric field.
2.4 Early Atomic Experiments
 Thomson’s “Plum Pudding Model”
 He postulated the ray was a steam of negatively
charged particles
 He named these particles “electrons.”
 Atoms are a diffuse cloud of positive charge with
negative electrons embedded in it.
 Atoms are electrically neutral
 Must have positive particles = “protons”
2.4 Early Atomic Experiments
 Robert Milikan (1868-1953)
“Oil Drop Experiment”
 Determined the mass of an electron
  9.11
2.4 Early Atomic Experiments
 Ernest Rutherford (1871-1937)
  x 10-31 kg
Tested the plum pudding model
“Gold Foil Experiment”
 Shot
radioactivity (α particles) at a thin piece of gold
foil.
 He expected the heavy α particles to pass right
through the foil with little, if any, deflection.
 What happened?
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2.4 Early Atomic Experiments
2.4 Early Atomic Experiments
 Rutherford dismissed the plum pudding
model.
 2.5 Modern Atomic Structure
Atoms must be mostly space with a center of
positive charge.
2.5 Modern Atomic Structure
 Nucleus
 Contains “protons”
 Positively
charged, equal in magnitude to the negative
charge of an electron.
 Contains “neutrons”
 Very small
 Equal
in mass to protons, but no charge.
2.5 Modern Atomic Structure
2.5 Modern Atomic Structure
 Why are atoms different from one another?
 Numbers of protons and electrons.
 Protons
= identity
= reactivity
 Electrons
 Numbers of neutrons
 Isotopes
– atoms with the same number of protons, but
different numbers of neutrons
Figure 2.15
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2.6 Molecules and Ions
 Chemical Bonds
 Covalent Bonds – electrons are shared between
atoms
 Molecules
 2.6 Molecules and Ions
 Structural Formula – indicates atoms and
individual bonds
have covalent bonds.
into the page
Chemical Formula – indicates the kind and
numbers of atoms in a compound
 e.g.
CO2
C6H12O6
H 2O
out of page
2.6 Molecules and Ions
 Ion – an atom or group of atoms that has a
net positive or negative charge
 Results from a gain (-) or loss (+) of electrons
Cation – positive ion
 Anion – negative ion
  Na+
 Cl-
2.6 Molecules and Ions
 Ionic Bonding – attraction between
oppositely charged ions
 Called “ionic solids” or “salts”
Cu2+ Fe3+
O2 -
N3 -
2.6 Molecules and Ions
Sodium Chloride
2.7 The Periodic Table
 Polyatomic Ions – “more than one atom
ions”
  See Table 2.5, p. 66
You will need to memorize these!
 Name,
formula, and Charge
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2.7 The Periodic Table
 Metals
Left and middle of table
 Shiny, good conductors, malleable
 Tend to lose electrons to form positive ions
  Non-metals
  Right side of table (and hydrogen)
Gain electrons to form negative ions
2.7 The Periodic Table
 Families or groups – vertical columns
Have similar chemical properties
Alkali metals – Group 1A
 Alkali earth metals – Group 2A
 Halogens – Group 7A
 Noble gases – Group 8A
   Periods – horizontal rows
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