Zumdahl’s Chapter 2 Atoms, Molecules, and Ions Chapter Contents History of Chemistry Mass &...
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Transcript of Zumdahl’s Chapter 2 Atoms, Molecules, and Ions Chapter Contents History of Chemistry Mass &...
Chapter Contents History of Chemistry Mass & Proportions Dalton Theory Subatomic Particles Structure of the
Atom Molecules and Ions
Periodic Table Symbols and
Organization Naming
Compounds Binary ionic
molecule Binary covalent
compounds Polyatomic ions
History of Chemistry 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 Mass unchanged in chemical
reactions Implies atoms conserved in reactions Elements combine in definite, simple
proportions by mass. Molecules are atoms in definite proportions! - Dalton
John Dalton (1808) 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 J.J. Thompson (1897) “cathode rays are electrons” (e–) and finds e/m ratio
Robert Millikan (1909) measures e and hence melectron known at 9.1110-31 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 Nucleons (protons and
neutrons) of almost the same mass (1.6710-27 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
3579Br
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
3581Br exist too in equal #s.
So isotope average A=80
Molecules and Ions 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 Z increases
linearly from 1H upper left
Groups (columns) have similar chemistry Alkali metals,
alkaline earths, transition metals, halogens and noble gases
Naming Compounds IONIC
Cation named first. If atom 1 makes
only one cation: Strontium chloride
SrCl2 If atom 1 makes
several cations: Iron(III) chloride
FeCl3
COVALENT Less electronegative
element named first Most electronegative
gets “anionic” –ide Greek prefixes show
proportions: Dichlorine heptoxide
Cl2O7
Mono prefix is never used for first atom.
Polyatomic Ions Few polyatomic cations
Most common: ammonium (NH4)+
Many polyatomic anions NO3
– nitrate, C2O42– oxalate, HSO4
– hydrogen sulfate, H2PO4
– dihydrogen phosphate, Cr2O7
2– dichromate ClO– hypochlorite, ClO2
– chlorite, ClO3–
chlorate, ClO4– perchlorate