1. Atomic Structure and Electron Configurations
Chemistry 2 Honors
J. Venables
Northwestern High School

2. 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.

3. 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)

4. Cathode Ray Tube – J. J. Thomson

5. Ernest Rutherford – Gold Foil Experiment

6. 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 ZAX.
Isotopes have the same Z but different A.
We find Z on the periodic table.

7. Examples Complete the following table: Symbol Protons Neutrons
Electrons
13H 12 13
35Cl 92
146

8. Examples Complete the following table: Symbol Protons Neutrons
Electrons
13H 1 2
1225Mg 12 13
35Cl 17 18
238U 92
146

9. The Atomic Mass Scale
1H weighs x g and 16O x g.
We define: mass of 12C = exactly 12 amu.
Using atomic mass units:
1 amu = x g
1 g = x 1023 amu

10. All waves have a characteristic wavelength, l, and amplitude, A.
Light and Waves
All waves have a characteristic wavelength, l, 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.
m∙s Hz (s-1) m