The Quantum Mechanical Picture of the Atom The

The Quantum Mechanical Picture of the Atom § The allowed energy states of atoms and molecules can be described by sets of numbers called quantum numbers n m ms 1

Quantum Numbers n n - the principal quantum number n n = 1, 2, 3, 4, . . . “shells” - the angular momentum quantum number n = 0, 1, 2, 3, … , n – 1 “subshells” = s, p, d, f, . . . m - the magnetic quantum number n n m = – , – + 1, … , – 1, ms - the spin quantum number n ms = – ½, + ½ 2

Quantum Numbers and Orbitals n n + n n n Define the energy of the electron Defines the shape of the orbital Orbital n The volume around the nucleus where the electron appears 90 -95% of the time The Pauli principle n No two electrons in an atom may have identical sets of four quantum numbers 3

s orbital ( = 0) n There is only one s orbital per n level 4

p orbital ( = 1) n There are 3 p orbitals per n level n They are named px , py , and pz 5

d orbital ( = 2) n There are 5 d orbitals per n level 6

f orbital ( = 3) n There are 7 f orbitals per n level 7

Order of Orbital Energy 8

Building Atoms 1) Build the nucleus by adding the required # of protons and neutrons according to the atomic # and mass # of the atom 2) Fill energy levels (orbitals) with the required # of electrons starting from the lowest available energy level and following Pauli and Hund rules (this is called Aufbau principle) 9

Building Atoms - Period 1 n m ms H He 10

Building Atoms - Period 2 n m ms Li Be 11

Building Atoms - Period 2 n m ms B C 12

Hund’s Rule Electrons occupy all the orbitals of a given subshell (with the same ) singly before pairing begins. These unpaired electrons have parallel spins (the same sign of ms). n m ms C 13

Building Atoms - Period 2 N O F Ne 14

Building Atoms - Period 3 Na P Mg S Al Cl Si Ar 15

Building Atoms - Period 4 K Ca Sc – 4 p or 3 d ? 16