Electron Configuration is the arrangement of electrons in an atom. Since low-energy systems are more stable than high-energy systems, electrons prefer the arrangement that gives the lowest possible energy. The most stable configuration is called the ground state electron configuration.

Orbital The space where there is a high probability that it is occupied by a pair of electrons. Orbitals are solutions of Schrodinger’s equations.

Orbitals

p orbitals and d orbitals p orbitals look like a dumbell with 3 orientations: p x, p y, p z (“p sub z”). Four of the d orbitals resemble two dumbells in a clover shape. The last d orbital resembles a p orbital with a donut wrapped around the middle.

Orbitals in Sublevels Sublevel # Orbitals # electrons s12 p36 d510 f714 g918

Three rules are used to build the electron configuration: Aufbau principle Pauli Exclusion Principle Hund’s Rule

Aufbau Principle Electrons occupy orbitals of lower energy first.

Electron Configurations Electrons fill the lowest energy levels first (calcium shown) 5s 4s 3s 2s 1s 2p 3p 4p 3d 4d ENERGYENERGYENERGYENERGY

-Pauli Exclusion Principle (Wolfgang Pauli, Austria, ) -Electron Spin Quantum Number An orbital can hold only two electrons and they must have opposite spin.

Hund’s Rule In a set of orbitals, the electrons will fill the orbitals in a way that would give the maximum number of parallel spins (maximum number of unpaired electrons). Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

Elements1s2s2px2py2pzElectron configuration H He Li B C N O F Ne

Zig Zag Rule TThis is used to remember the filling order for electron configuration. REMEMBER: “s” holds 2; “p” holds 6 & “d” holds 10; “f” holds 14 EXAMPLES: Mg-12 Ge-32

When figuring our Ge: 1s 2 2s 2 2p 6  so far 10 electrons (neon) 1s 2 2s 2 2p 6 3s 2 3p 6  so far 18 electons (argon) ANSWER: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2 Could also be written as [Ar] 4s 2 3d 10 4p 2 This is called a kernal. The kernal is the highest noble gas structure within the configuration. In this case it is argon. It is good to write out the configuration of noble gases to use when dealing with large # of electrons.

Shorthand Notation Use the last noble gas that is located in the periodic table right before the element. Write the symbol of the noble gas in brackets. Write the remaining configuration after the brackets. Ex: Fluorine: [He] 2s 2 2p 5

Exceptions to the Rule Chromium, copper & their families undergo electron promotion Should be: Cr=[Ar]4s 2 3d 4 Cu=[Ar] 4s 2 3d 9 but these configurations leave ½ empty orbitals so their configurations are Cr=[Ar]4s 1 3d 5 Cu=[Ar] 4s 1 3d 10

Electron Configuration of Ions Ex. 1Cl - Atomic # = 17 but a negative ion so you have to add 1 to the atomic number so the atomic # is 18 Ex. 2Ca 2+

Ex. 3Fe 2+ Ex. 4Fe 3+

Valence Configuration Step 1: Write the complete configuration F = 9 Ge = 32 Step 2: Choose the electrons if the highest energy level.

Blocks in the Periodic Table