Atomic Structure and Electron Configurations Chemistry 2 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 ZAX. Isotopes have the same Z but different A. We find Z on the periodic table.

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

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

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

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-1 Hz (s-1) m