4.8 – NOTES Intro to Electron Configurations

II. Quantum Theory and the Atom A. Bohr model of the atom – 1913 1. Energy states of hydrogen (only certain allowable energy states) Ground state: lowest allowable energy state, Bohr proposed e- resides in an orbit, the smaller the orbit, the lower the energy; assigned a number (n) to each orbit and calculated the radius of each orbit Excited State: occurs when an electron gains energy; will quickly release energy, usually in the form of light

2. An explanation of hydrogen’s line spectrum - expected discontinuous, suggested in ground state with an n = 1, when energy added electron moves to excited state (n=2), moves to ground state and emits energy/photon; - shows H actually moves to N = 3, 4, or 5 energy level and drops to 2nd; gives us spectrum; could only describe H;

Hydrogen – 1 electron, multiple levels of excitement!!!!!

B. The quantum mechanical model of the atom 1. Electrons as waves Bohr’s quantized orbits similar to waves; The de Broglie relation – 1924 λ = h/mν; all moving particles have wave-like characteristics; only visible in small particles like electrons

C. The Heisenberg Uncertainty Principle 1. It is impossible to make a measurement on an object without disturbing the object in some way, especially if the object is very small. - Heisenberg’s Uncertainty Principle states that impossible to know the speed and location of an electron at the same time

2. The Schrödinger wave equation – 1926 does nothing to describe the electron path around the nucleus, - predicts a region around the nucleus where the electron might be located; 3. Atomic orbitals 3 – dimensional region around the nucleus where electrons can be found. An orbital has no definite outer boundary. An orbital is also called a probability function.

D. Hydrogen’s atomic orbitals 1. The position of an electron is described by 4 quantum numbers: Principal quantum number, n - energy level of the electron (for H); relates the average distance of the electron from the nucleus in an orbital Sublevel quantum number, ℓ - Angular Momentum Quantum Number; gives us shape; aka called orbital quantum # Magnetic quantum number, mℓ - orientation in space Spin quantum number, ms

2. The 7 energy levels Energy Level Shell # of Sublevels   # of Sublevels Sublevels Present Sublevel Names # of orbitals (n2) # of e- (2n2) 1 K s 1s 2 L s,p 2s, 2p 4 8 3 M s, p, d 3s, 3p, 3d 9 18 N s, p, d, f 4s, 4p, 4d, 4f 16 32 5 O s, p, d, f, g 5s, 5p, 5d, 5f, 5g 25 50 6 P s, p, d, f, g, h 6s, 6p, 6d, 6f, 6g, 6h 36 72 7 Q s, p, d, f, g, h, i 7s, 7p, 7d, 7f, 7g, 7h, 7i 49 98 2. The 7 energy levels

s = sharp (defined) d = diffuse (spread out) p = principle (very strong) f = fundamental