Atomic Structure and Electron Configurations

1. Atomic Structure and Electron Configurations Chemistry I 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:

8. Examples Complete the following table:

9. 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 g • 1 g = 6.02214 x 1023 amu

10. 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-1 Hz (s-1) m