Quantum Mechanics

Electron Density Gives the probability that an electron will be found in a particular region of an atom Regions of high electron density represent a high probability of locating the electron Representation of the electron density distribution surrounding the nucleus in the hydrogen atom; shows a high probability of finding the electron closer to the nucleus Based on Heisenberg uncertainty principle and Schrodinger wave equation

Atomic Orbital Way to distinguish Bohr’s model from the current quantum mechanical model Probability of locating the electron in 3D space around the nucleus Has a characteristic energy

Quantum numbers used to describe atomic orbitals and to label electrons that reside in them Principle quantum number (n) Angular momentum quantum number Magnetic quantum number Electron spin quantum number

5 n = 1, 2, 3, 4, …. n=1 n=2 n=3 distance of e - from the nucleus Principal Quantum Number n

Energy levels are like rungs of a ladder. You cannot be in between a rung Energy levels in an atom’s electron are unequally spaced. The higher energy levels are closer together.

Angular Momentum Quantum Number Shape of the “volume” of space that the e - occupies s orbital p orbital d orbital f orbital smart people do fine

Magnetic Quantum Number Describes the orientation of the orbitals in space All orientations are identical in energy

s orbital Sphere

p orbital dumbbell3 orientations

d orbital Double dumbbell 5 orientations

f orbital 7 orientations

Electron Spin Quantum Number Electrons are thought to be spinning on their own axes-clockwise, or counterclockwise. The up and down arrows denote the direction of the spin.

Energy of Orbitals depends on principle and angular momentum quantum numbers

Shielding Effect Why is the 2s orbital lower in energy than the 2p? “shielding” reduces the electrostatic attraction Energy difference also depends on orbital shape

Electron Configuration vs Orbital diagram 1s 1 principal quantum number n Shape number of electrons in the orbital Orbital diagram H 1s 1

Aufbau Principle “fill up” the lowest energy level first

Orbitals in the Periodic Table

Pauli Exclusion Principle No two electrons can have the same 4 quantum numbers Only two electrons may occupy the same atomic orbital, and these electrons must have opposite spins Electrons that have opposite spins are said to be paired Orbital name# of orientationsTotal # of electrons s p d f

Hund’s Rule The most stable arrangement of electrons in an orbital is the one with the greatest number of parallel spins e- will occupy singly before filling with opposite spins

Practice Fill in the orbital diagram, and write the electron configuration for the following atoms

Example of Exceptions to the Rules ElementShould beActually is Copper1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 Chromium1s 2 2s 2 2p 6 3s 2 3p 6 3d 9 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 These are not the only two exceptions. The rules are violated because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations

Noble Gas Configuration What is the electron configuration for Ne? Ne: What is the electron configuration for Mg? Mg: What do both electron configurations have in common?

To figure out which noble gas to use find the noble gas that is closest to the element without going over in atomic number Which noble gas is closest without going over? Rb Cl Ra

Practice Write the noble gas electron configuration for the following atoms: Na: Mn: Co: Sn:

Valence Electrons Electrons in the outermost s and p orbitals (highest n shell) These electrons participate in chemical reactions