1. ATOMS: THE BUILDING BLOCKS OF MATTER Chapter 3

5. Who are these men? In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

22. Thomson concluded that the negative charges came from within the atom. A particle smaller than an atom had to exist . The atom was divisible! Thomson called the negatively charged “ corpuscles, ” today known as electrons . Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. But he could never find them.

35. Wave Model

40. Indivisible Electron Nucleus Orbit Electron Cloud Greek X Dalton X Thomson X Rutherford X X Bohr X X X Wave X X X

44. Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p + + n 0 8 8 18 18 Arsenic 75 33 75 Phosphorus 15 31 16 Nuclide p + n 0 e - Mass # Oxygen - 10 - 33 42 - 31 15

51. Isotopes are atoms of the same element having different masses , due to varying numbers of neutrons. Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 1 0 Hydrogen-2 (deuterium) 1 1 1 Hydrogen-3 (tritium) 1 1 2