Zumdahl’s Chapter 2
Atoms, Molecules, and Ions
Chapter Contents
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History of Chemistry
Mass & Proportions
Dalton Theory
Subatomic Particles
Structure of the
Atom
Molecules and Ions
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Periodic Table
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Symbols and
Organization
Naming Compounds
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Binary ionic molecule
Binary covalent
compounds
Polyatomic ions
History of Chemistry
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Democritus (5th Century BC) atomic
postulate
Lucretius (1st Century AD) “atoms and
the void”
Priestly (18th Century AD) discovers
oxygen
Lavoisier (18th) diamond=carbon
Conservation of Mass and
Chemical Proportions
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Mass unchanged in chemical reactions
Implies atoms conserved in reactions
Elements combine in definite, simple
proportions by mass.
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 Molecules are
atoms in definite
proportions! - Dalton
John Dalton (1808)
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Elements are collections of identical,
miniscule atoms.
Different elements differ in their atoms.
Compounds are combinations of
different elements.
Under reaction, compounds rearrange
their atoms.
Subatomic Components
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J.J. Thompson (1897) “cathode rays are
electrons” (e–) and finds e/m ratio
Robert Millikan (1909) measures e and hence
melectron known at 9.1110-31 kg
E. Rutherford (1906) bounces  (He2+) off Au
tissue proving protons (p+) in nucleus
F.A. Aston (1919) “weighs” atomic ions
J. Chadwick (1939) observes neutrons (no
charge) by decomposition (to p+, e–, and ).
Structure of the Atom
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Nucleons (protons and
neutrons) of almost the
same mass (1.6710-27 kg)
live in nucleus (R~2 fm).
Electrons occupy the full
atomic radius (R~50 pm),
shielding the nucleus.
Electron and proton count
identical in neutral atom.
Symbology of an Atom
79Br
35
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Z=35 is bromine’s atomic
number (count of protons)
A=79 is its mass number
(count of all nucleons)
So 3579Br has 79–35 or 44
neutrons
81Br exist too in equal #s.
35
So isotope average A=80
Molecules and Ions
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Atoms in molecules share (covalent) or
steal (ionic) electrons to bond.
Stolen electrons lead to attraction of
unlike charged ions (ionic bonding)
Directional electron “clouds” lead to
molecular shapes.
Molecules can be ionic as well as atoms.
Periodic Table
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Z increases linearly
from 1H upper left
Groups (columns)
have similar
chemistry
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Alkali metals,
alkaline earths,
transition metals,
halogens and noble
gases
Naming Compounds
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IONIC
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Cation named first.
If atom 1 makes only
one cation:
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Strontium chloride
SrCl2
If atom 1 makes
several cations:
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Iron(III) chloride
FeCl3
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COVALENT
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Less electronegative
element named first
Most electronegative
gets “anionic” –ide
Greek prefixes show
proportions:
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Dichlorine heptoxide
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Mono prefix is never
Cl2O7
used for first atom.
Polyatomic Ions
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Few polyatomic cations
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Most common: ammonium (NH4)+
Many polyatomic anions
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NO3– nitrate, C2O42– oxalate, HSO4–
hydrogen sulfate, H2PO4– dihydrogen
phosphate, Cr2O72– dichromate
ClO– hypochlorite, ClO2– chlorite, ClO3–
chlorate, ClO4– perchlorate
Naming Exercise
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Al2(S2O3)3
P4O10
Cu(NO2)2
NaMnO4
CS2
Fe2(CrO4)3
HCl (gas)
PH4BrO2
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Aluminum thiosulfate
Tetraphosphorous
decaoxide
Copper(II) nitrite
Sodium permanganate
Carbon disulfide
Iron(III) chromate
Hydrogen chloride
Phosphonium bromite