Atomic Structure and Electron Configurations Chemistry I Honors J. Venables Northwestern High School
Dec 31, 2015
Atomic Structure and Electron Configurations
Chemistry I Honors
J. Venables
Northwestern High School
Atomic Structure and the Periodic Table
• John Dalton’s Atomic Theory:– Each element is composed of atoms
– All atoms of an element are identical. The atoms of different elements are different.
– In chemical reactions, the atoms are not changed; they are rearranged.
– Compounds are formed when atoms of more than one element combine.
• Law of Definite Proportions –– A given compound always has the same
proportion (H2O, NaCl)
• Law of Conservation of Mass –– In a chemical reaction, mass is neither
created nor destroyed.
• Law of Multiple Proportions –– Different compounds can exist with different
ratios of the same elements (H2O, H2O2)
– (CO, CO2) (N2O, NO2)
Cathode Ray Tube –J. J. Thomson
Ernest Rutherford –Gold Foil Experiment
Isotopes, Atomic Numbers, and Mass Numbers
• Atomic number (Z) = number of protons in the nucleus.
• Mass number (A) = total number of nucleons in the
nucleus (i.e., protons and neutrons).• By convention, for element X, we write Z
AX.• Isotopes have the same Z but different A.• We find Z on the periodic table.
ExamplesComplete the following table:
Symbol Protons Neutrons Electrons
13H
12 13 12
35Cl
92 146 92
ExamplesComplete the following table:
Symbol Protons Neutrons Electrons
13H 1 2 1
1225Mg 12 13 12
35Cl 17 18 17
238U 92 146 92
The Atomic Mass Scale• 1H weighs 1.6735 x 10-24 g and 16O 2.6560 x 10-23
g.• We define: mass of 12C = exactly 12 amu.• Using atomic mass units:
1 amu = 1.66054 x 10-24 g1 g = 6.02214 x 1023 amu
Light and Waves• All waves have a characteristic wavelength, , and
amplitude, A.• The frequency, f, of a wave is the number of cycles
which pass a point in one second.• The speed of a wave, v, is given by its frequency
multiplied by its wavelength:
• For light, speed = c.
fc m∙s-1 Hz (s-1) m