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NOTES 2 ATOMIC STRUCTURE MON 5/23/2011 SUBATOMIC PARTICLES Mass (in amu) Charge Location Proton 1 +1 nucleus Neutron 1 0 nucleus -1 outside the nucleus in orbitals Electron 1/2000th Atomic Number:# of protons Overall Charge: (# of protons) – (# of electrons) Atomic Mass: (# of p’s + # of n’s) Nuclear Charge = atomic # ISOTOPES Two atoms with the same # of protons (atomic #) but different #’s of neutrons (atomic masses) are ISOTOPES of the same element ALLOTROPES Two forms of the same element with different structural and physical properties (O2 and O3) 203 YEARS OF ATOMIC THEORY DALTON (1808): The atom is a SOLID BALL THOMPSON (1891):The atom is a positively charged jelly with electrons spread throughout RUTHERFORD(1908):The atom is mostly empty space with a massive (+) nucleus WAVE-MECHANICAL MODEL (1920-today): Electrons in the atom are to be found 90% of the time in 3D regions called orbitals THE BOHR ATOM When an electron transitions from the excited to the ground state, the atom loses energy When an electron transitions from the ground to the excited state, the atom absorbs energy Ground State Electron Configuration of Sulfur: 2 – 8 – 6 Excited State Sulfur: 2 – 8 – 5 – 1 THE WEIGHTED AVERAGE OF NATURALLY OCCURING ISOTOPES Weighted average = (mass of isotope #1) x (% abundance) + (mass #2) x (%) + … 100%
