2.4- Quantum Mechanical Model

Quantum Numbers 2px↑ Principle Angular momentum Magnetic Spin Each electron must have a different location (atomic orbital) in the atom The electrons are described by four quantum numbers. Principle Angular momentum Magnetic Spin 2px↑

Principle Quantum Number Energy Level where the electron is located Numbered 1 to 7 out from the Nucleus level 1 holds 2 electrons level 2 holds 8 electrons level 3 holds 18 electrons level 4 holds 32 electrons These energy levels correspond to the periods on the periodic table

Angular Momentum Quantum Number Shape of the atomic orbital The shapes are s, p, d, f (you must know these!) s are spherical p are dumbbell d are double- dumbbell f are quadruple-dumbbell Shape Suborbitals s 1 p 3 d 5 f 7 Energy Level Shapes 1 s 2 s,p 3 s,p,d 4-7 s,p,d,f

Spin Quantum Number Each atomic suborbital can hold 2 electrons Electrons spin like a top Pauli Exclusion Principle No 2 electrons can have the same set of four quantum numbers 2 electrons paired in the same orbital must spin in opposite directions If one is clockwise the other is counterclockwise Spin is shown as ↑ or ↓

Aufbau Principle Electrons occupy the orbitals of lowest energy first Note: orbitals with the same energy level and shape have the same energy regardless of orientation The Periodic Table is a guide for the Aufbau Principle, going from left to right as you move down the periodic table Each element represents one electron

Orbital Diagrams Each atomic suborbital has a box (2 electrons per box) Hund’s Rule: Give each orbital (of equal energy) one electron before any get two electrons

Sample Problems O Fe N He Example: Be 1s2, 2s2 [He], 2s2 Write the electron configuration, the shorthand and draw the orbital diagram for the following elements: O Fe N He Example: Be 1s2, 2s2 [He], 2s2

Lewis Structures • • • N • • Bohr model • • • • N • • • Place only valence electrons around the element symbol • N • • Bohr model • • • • draw all electrons in the appropriate levels N • • •