Chapter 2 Atoms, Molecules, and Ions.docx - Chapter 2:...

Chapter 2: Atoms, Molecules, and Ions
Section 2.1— The Early History of Chemistry
Early History of Chemistry
 Greeks were the first to attempt to explain why chemical changes occur
 Alchemy dominated for 2000 years
 Several elements discovered
 Mineral acids prepared
 Robert Boyle was the first “chemist”
 Performed quantitative experiments
 Developed first experimental definition of an element
Section 2.2 – Fundamental Chemical Laws
Conversions Using Prefixes
 Convert 347 ng to kg
 Convert 0.00123 in to m
Square Unit Conversion
 A soccer field has a grassy area that is 1.452 x 10 4 m 2 . If a lawn mower can cut 468
in
2
/minute, how many hours will it take to mow the field (1 in=2.54 cm)?
One More Conversion
 A CD has a thickness of 0.134 cm. How many CD’s are needed to form a stack of CD’s
EXACTLY 1 mile high (1 mile=5280 ft., 1ft= 12 in, 1 in = 2.54 cm)?
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Three Important Laws
 Law of conservation of mass (Lavoisier):
 Mass is neither created nor destroyed in a chemical reaction
 Law of definite proportion (Proust):
 A given compound always contains exactly the same proportion of elements by
mass
 Law of multiple proportions (Dalton):
 When two elements form a series of compounds, the ratios of the masses of the
second element that combine with 1 gram of the first element can always be
reduced to small whole numbers
Section 2.3 – Dalton’s Atomic Theory
Dalton’s Atomic Theory (1808)
 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 or ways
 Chemical compounds are formed when atoms of different elements combine with each
other. A given compound always has the same relative numbers and types of atoms.
 Chemical reactions involved reorganization of the atoms—changes in the way they are
bound together
 The atoms themselves are not changed in a chemical reaction
Gay-Lussac and Avogadro (1809-1811)
 Gay-Lussac
 Measured (under same conditions of T and P) the volumes of gases that reacted
with each other
 Avogadro’s Hypothesis
 At the same T and P, equal volumes of different gases contain the same number of
particles
 Volume of a gas is determined by the number, not the size, of molecules
Representing Gay—Lussac’s Results
Section 2.4 – Early Experiments to Characterize the Atom
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J.J. Thomson (1898-1903)
 Postulated the existence of negatively charged particles, that we now call electrons, using