Download Chapters 3

Chapters 3 - 4
How It All Fits Together
Developing a model of the atom
in order to explain, predict and
perform chemical reactions and
chemical properties.
3.1 Atom: History (Democritus to Rutherford)
• Democritus – indivisible particle (atomos)
• Dalton – Atomic Theory
(e.g. atoms are rearranged, combined, or
separated)
• Thomson
- Cathode-ray tube (CRT)
- discovered electron
- plum-pudding model
• Rutherford
- gold-foil; discovered nucleus; Nuclear Model
Historical Development of Atomic Models
(side information)
• atomic number = #protons
• mass number = #protons + #electrons
• charge
= difference between #protons & #electrons
much of what we know (atoms) comes from light
• light travels in waves
• c=ln
• E=hn
(energy of a photon; h = Plank’s constant)
• E = (h c) / l
• Plank – energy comes in quanta
(discrete packets of energy; not continuous)
(photon ~ light quanta)
• Bohr – electrons in fixed orbits
– are separated by quanta
– experiment: line-emission spectrum of
hydrogen atom
• dual wave-particle theory explained fixed orbits
(analogy: musical scale A, B, ...)
• Heisenberg’s uncertainty principle
- probable location of an electron
• Schrödinger’s wave equation:
- () gives the probable location of an electron in
x-, y-, z-, and time coordinates.
• Quantum numbers (location of electron):
- “n” = principle q.n. (principle energy level)
- “l” = angular q.n. (shape s-, p-, etc)
- “m” = magnetic q.n. (orientation)
- “s” = spin (+ ½; )
• Orbital Notation (e.g., sulfur)
• Electron Configuration
1s2 2s2 2p6 3s2 3p3
• Noble-Gas Configuration
[Ne] 3s2 3p3