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The atom’s history and theories
The atom’s history and theories
media.nasaexplores.com/.../images/faucet2.jpg
Early History
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.www.mlahanas.de/Greeks/images/Leucippus1.jpg
There must be ultimate tiny particles
of water that could not be further subdivided.
Look at the sand at the beach!
Leucippus
Early History
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.web.mit.edu/philos/www/mm/democritus.jpg
I’ll name these indivisible particles
atomos (which means indivisible).
These atoms are distinct in shape and
size!
Democritus 460 – 370 BC460 – 370 BC
Early History
There are only four elements!
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.www.brown.edu/.../Images/0506/GREEKS131.jpg
Earth Water
Air Fire
Law of Conservation of Mass
Antoine Lavoisier
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.http://www.lepla.edu.pl/fr/modules/Activities/m40/images/lavois03.jpg
When a chemical reaction is carried
out in a closed system, the total
mass of the system does not
change!
1743 – 17941743 – 1794
Law of Conservation of Mass: The total mass of the system does not change
reactant 1 + reactant 2 product
total mass total mass=
calcium oxide + carbon dioxide calcium carbonate
56.08 g + 44.01 g 100.09 g
Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.
Law of Definite Composition
Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.http://www.provincia.ps.it/ls.laurana/tempo/proust.jpg
A given compound always contains its
constituent elements in certain fixed
proportions by mass!
Proust1754 – 1826 1754 – 1826
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.http://clendening.kumc.edu/dc/pc/berzelius.jpg
http://elements.vanderkrogt.net/images/Lead.jpg http://www.theodoregray.com/PeriodicTable/Samples/082.6/s7s.JPG
10.00 g lead
1.56 g sulfur
11.56 g lead
sulfide
Law of Definite Composition: No matter the mode of preparation, a particular compound is composed of
the same elements in the same mass fractions
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.http://clendening.kumc.edu/dc/pc/berzelius.jpg
http://elements.vanderkrogt.net/images/Lead.jpg http://www.theodoregray.com/PeriodicTable/Samples/082.6/s7s.JPG
10.00 g lead
11.56 g lead
sulfide
3.00 g sulfur
1.44 g sulfur
left-over
Law of Definite Composition: No matter the mode of preparation, a particular compound is composed of
the same elements in the same mass fractions
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.http://clendening.kumc.edu/dc/pc/berzelius.jpg
http://elements.vanderkrogt.net/images/Lead.jpg
18.00 g lead
1.56 g sulfur
11.56 g lead
sulfide
8.00 g lead
left-over
Law of Definite Composition: No matter the mode of preparation, a particular compound is composed of
the same elements in the same mass fractions
Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.
Analysis by MassAnalysis by Mass(grams/20.0 g)(grams/20.0 g)
Mass FractionMass Fraction(parts/1.00 part)(parts/1.00 part)
8.0 g calcium8.0 g calcium2.4 g carbon2.4 g carbon9.6 g oxygen 9.6 g oxygen
20.0 g20.0 g
0.40 calcium0.40 calcium0.12 carbon0.12 carbon0.48 oxygen 0.48 oxygen
1.00 part by mass1.00 part by mass
Law of Definite Composition: No matter the source, a particular compound is composed of the same elements in the same mass fractions
Law of Multiple Proportions
Hill, J. and D. Kolb. 1995. Chemistry for Changing Times 7th ed. Phils: Prentice-Hall, Inc.http://cache.eb.com/eb/image?id=8421&rendTypeId=4
Elements can combine in more than one set of
proportions, and each set corresponds
to a different compound!
Dalton 1766 – 18841766 – 1884
Law of Multiple Proportions: Elements can combine in more than one set of proportions
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
• Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass, and chemical properties. The atoms of one element are different from the atoms of all other elements.
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
• Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction
• Supports–Law of Definite Composition–Law of Multiple Proportions
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
• A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction– Supports the Law of Conservation of
Mass
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
Atomic Theory
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
++
Based on Dalton’s Atomic Theory, the atom is
the basic unit of an element that can enter into a chemical reaction extremely small indivisible
Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.
