Lecture Outline
Matter & Early Atomic Theory
Classification of matter
• Mixtures, pure substances, compounds, elements
Elemental symbols
• Know the names and symbols of the first 36 elements.
• What's the difference between CO and Co? Ca and CA?
Tour of the periodic table
• Group numbers, alkali metals, alkaline earth metals, chalcogens, halogens, noble gases,
metals/nonmetals/metalloids, transition metals, lanthanides, actinides
John Dalton's Atomic Theory (1850).
• Elements are composed of indivisible particles called atoms.
• Atoms of the same element are identical, and unlike the atoms of any other element.
• Atoms combine to form compounds.
• Chemical reactions involve rearrangements of atoms to form new compounds.
• Which of the above parts of Dalton's Atomic Theory are known today to be inaccurate?
Early Thoughts of the Atom.
• Empedocles (440 BC): Earth, Air, Fire, and Water.
• Democritus (400 BC): Matter is composed of indivisible particles called "atoms."
Unfortunately, Aristotle disagreed, saying that matter is continuous, so the "atomic
theory" was disregarded until centuries later.
Experimental Evidence for Atoms.
• Conservation of Mass: Lavoisier used precise measurements of mass in a closed system
to show that mass is conserved when mercury (II) oxide is heated to produce metallic
mercury and gaseous oxygen.
• Constant Composition: Compounds have the same composition, no matter how they are
formed. For example, carbon dioxide has the same ratio of carbon and oxygen whether it
is formed from the combustion of coal or the respiration of a guinea pig.
• Definite Proportions: Elements combine in the same proportions. Lead (II) sulfide.
• Multiple proportions: Atoms combine in small whole number ratios to form compounds.
Different ratios are different compounds.
Electricity Experiments
• Michael Faraday - Charged atoms carry electric current.
• Svante Arrhenius - An "ion" is an atom which carries a charge.
• William Crookes - Invented the cathode ray tube, which was used to discover electrons
and protons. A perforated cathode helped in the discovery of positive rays moving in a
direction opposite to the cathode rays.
• J.J. Thompson proposed a "raisin-pudding" model of the atom to explain the cathode ray
tube experiments.
Rutherford's gold foil experiment resulted in a new nuclear model of the atom in which the
positive charge is concentrated in a "nucleus" and the electrons are orbiting outside of the
nucleus.
Lecture Outline
Matter & Early Atomic Theory
Subatomic particles – protons, neutrons, electrons
Proton
Neutron
Electron
Charge
+1
0
-1
Mass
1
1
0
Elemental symbols (Nuclear symbols)
•
Example for a particle with 15 protons, 14 neutrons, and 18 electrons:
•
This is a phosphorus-29 atom with a –3 charge.
29 3P
15
Isotopes
• Same number of protons, different number of neutrons
• Same atomic number, different atomic mass
Average atomic masses (based on abundance)
• It’s a weighted average of atomic masses based on the abundance of each isotope.
• The periodic table shows these averages.
• The periodic table does not show the atomic mass of any individual atom. These are
shown in nuclear symbols for the particular atom.
Compounds
• A molecule is the smallest particle of a compound that can exist. Know what an ion is,
and the difference between an anion and a cation.
• Which elements typically form anions? cations?
• What are covalent/ionic compounds?
Elements that exist naturally as Diatomic Molecules.
• Know these (H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 , At2 ), but remember, this is only for the pure
element. These elements exist in compounds with other elements as single atoms.
Chemical Formulas.
• Know how to interpret these.
• Compare mixtures against compounds. What's the difference?