ATOM     The atom--basic building block of all matter   Components of Atoms    Charge  Mass (atomic mass units) protons  +  1 electrons - 1/1850 = 0.00054 neutrons nil  1   I. ATOMIC THEORIES A. Bohr theory 1. Named after Niels Bohr (1917) 2. Nucleus (protons and neutrons) surrounded by electrons in "shells"/ "orbitals"/ "clouds" B. Heisenberg Uncertainty Principle 1. At any instant, the exact location of an electron is indeterminable II. ATOMIC CONCEPTS A. Atomic number = # of protons in an atom B. Atomic mass (weight) = # of protons + # of neutrons III. EFFECT OF ATOMIC CHANGES A. Effects of varying # of protons 1. 1H (hydrogen) add a proton--> 2H4 (helium) 2. Changes the atom to an atom of another element 3. Periodic table--arrangement of successive groups of elements according to their chemical behavior a. 92 naturally occuring elements e.g. 1H1 92U238 b. 80-90% by weight of the earth: Fe--35-40% O--25-30% Si--13-15% Mg--10% B. Effects of varying # of neutrons 1. Isotope--different atoms of the same element with varying numbers of neutrons a. 1H1 - most simple form b. 1H2--deuterium (heavy hydrogen) c. 1H3--tritium d. 92U238 e. 92U235--fissionable one out of every 144 U atoms will be the U235 isotope C. Effects of varying number of electrons 1. Atoms are electrically stable 2. Ions--atoms that gain or lose an electron a. Cations--positive charge b. Anions--negative charge 3. Stable noble gas configuration: outer electron shell is filled a. He--Helium b. Ne--Neon c. Ar--Argon d. Kr--Krypton e. Xn--Xenon f. Rn--Radon 4. Ionization - two examples  11Na23 17CL35 11 protons 17 protons 12 neutrons 18 neutrons 11 electrons 17 electrons Na - e- --> Na+1 Cl + e- --> Cl-1