The Quantum Model of the Atom

Quantum Mechanical Model The quantum mechanical model makes no attempt to predict the path of an electron around the nucleus Bohr orbits were replaced with quantum-mechanical orbitals Orbitals are different from orbits in that they represent probability maps that show a statistical distribution of where the electron is likely to be found

Quantum Mechanical Model In this model, a number and a letter specify an orbital or energy level As value of “n” increases, orbital becomes larger Electrons spend more time away from nucleus Each orbital level can hold a maximum of 2 electrons “n” = an atom’s principal energy level

Principal Energy Sublevels Sublevels = “s”, “p”, “d”, & “f” distinctions Correspond to shape of atom’s orbitals All “s” orbitals = spherical; all “p” orbitals = dumbbell-shaped; “d” and “f” vary

Principle Energy Sublevels The lowest-energy orbital is called the 1s orbital – specified by the number 1 and the letter s. Two sublevels in P.E.L 2 – 2s and 2p 2s sublevel is same shape, larger size than 1s 2p sublevel has 3 dumbbell-shaped p orbitals of equal energy (2px, 2py, 2pz)

Principle Energy Sublevels P.E.L. 3 contains 3 sublevels (3s, 3p, & 3d) “s” and “p” sublevels are same “d” sublevel contains 5 orbitals of equal energy P.E.L 4 contains 4 sublevels (4s, 4p, 4d, & 4f) “s”, “p”, & “d” sublevels are same “f” sublevel contains 7 orbitals of equal energy

S-sublevel

P-sublevel

D-sublevel

F-sublevel

Review Bohr predicted that electrons orbited the nucleus like plants orbit the sun de Broglie hypothesized that electrons behave like waves Schrodinger predicted existence of atomic orbitals contained electrons Orbitals existed within the energy levels

Electron Configuration Overview of the arrangement of electrons in an atom Electrons tend to take position of lowest energy, making low energy systems more stable than high An atom’s Ground State = most stable configuration This is the reason that valence electrons are the most active!!

Let’s follow the RULES! Aufbau Principle Each e- occupies lowest energy orbital available Orbitals are filled completely from lowest to highest energies s  p  d  f

Pauli exclusion principle: A maximum of 2 e- may occupy a single orbital level e- spin in one of two directions Up arrows indicate one direction, down arrows opposite Atomic orbitals that are FULL are represented as

Hund’s rule: Single e- with same spin must occupy each orbital before e- with opposite spins are added Good example looks at “p” orbitals

Orbital Diagrams Method 1 for showing an atom’s electron configuration 1 box for every orbital Empty boxes = unoccupied orbitals Each box labeled with the principal quantum # and sublevel associated with the orbital

Let’s work some examples!! H C Ne Mg Ge Au

Electron Configuration Notation Shows P.E.L and energy sublevel associated with each of the atom’s orbitals Includes superscript representing # of e- in orbital DOES NOT INCLUDE arrows!!

Electron Configuration Notation examples… B Be O Si Nb

Noble Gas notation Represents e- configuration using brackets and symbols of Noble Gases [He] = 1s2 [Ne] = 1s22s22p6 Using noble gas of most previous one, write e- configuration notation of elements

Noble Gas notation examples…. Li Na K Si S Eu

Valance E- and Configurations Valence electron = e- in outermost energy level Determines reactivity Can use Noble Gas configuration notation to determine valence numbers S = [Ne]3s23p4 Cs = [Xe]6s1 Fr = [Rn]7s1 Simply add the exponents from the notation