The Aufbau Principle

 Assumes that all atoms have the same type of orbitals that the Hydrogen atom does  As Protons are added to the nucleus to build up the elements, similarly electrons are added to the hydrogen like orbitals  Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom.

1s11s1 row # shell # possibilities are rows subshell possibilities are s, p, d, or f 4 subshells group # # valence e- possibilities are: s: 1 or 2 p: 1-6 d: 1-10 f: 1-14 Total e- should equal Atomic # What element has an electron configuration of 1s 1 ?

 Lithium: 1. find the element on the periodic table 2. what is the period number? 3. how many shells? 4. what is the group number? 5. how many valence electrons? 6. what subshell(s) does Li have? 7. what is the electron configuration? atomic # = s 1s 2 2s 1

 Boron: 1. find the element on the periodic table 2. what is the row #? 3. how many shells? 4. what is the group #? 5. how many valence electrons? 6. what subshell(s) does B have? 7. what is the electron configuration? atomic # = p 1s 2 2s 2 2p 1

ORBITALS AND THE PERIODIC TABLE  Orbitals grouped in s, p, d, and f orbitals (sharp, proximal, diffuse, and fundamental) s orbitals p orbitals d orbitals f orbitals

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f 6f Orbitals available to a Hydrogen atom

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f With more electrons, repulsion changes the energy of the orbitals.

NO MORE THAN 2 ELECTRONS IN ANY ORBITAL…EVER. The next rule is the Pauli Exclusion Principal. The next rule is the Pauli Exclusion Principal. The Pauli Exclusion Principle states that an atomic orbital may have up to 2 electrons and then it is full. The Pauli Exclusion Principle states that an atomic orbital may have up to 2 electrons and then it is full. The spins have to be paired. The spins have to be paired. We usually represent this with an up arrow and a down arrow. We usually represent this with an up arrow and a down arrow. Since there is only 1 s orbital per energy level, only 2 electrons fill that orbital. Since there is only 1 s orbital per energy level, only 2 electrons fill that orbital. Wolfgang Pauli, yet another German Nobel Prize winner

Increasing energy 1s 2s 3s 4s 5s 6s 7s 2p 3p 4p 5p 6p 3d 4d 5d 7p 6d 4f 5f He with 2 electrons

HUND’S RULE Hunds Rule states that when you get to orbitals, you fill them all half way first, and then you start pairing up the electrons. Hunds Rule states that when you get to orbitals, you fill them all half way first, and then you start pairing up the electrons. Don’t pair up the 2p electrons until all 3 orbitals are half full.

 Valence electrons- the electrons in the outermost energy levels (not d).  Core electrons- the inner electrons  Hund’s Rule- The lowest energy configuration for an atom is the one have the maximum number of unpaired electrons in the orbital.  C 1s 2 2s 2 2p 2

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2

 A way of abbreviating long electron configurations  Since we are only concerned about the outermost electrons, we can skip to places we know are completely full (noble gases), and then finish the configuration

 Step 1: It’s the Showcase Showdown! Find the closest noble gas to the atom (or ion), WITHOUT GOING OVER the number of electrons in the atom (or ion). Write the noble gas in brackets [ ].  Step 2: Find where to resume by finding the next energy level.  Step 3: Resume the configuration until it’s finished.

 Chlorine  Longhand is 1s 2 2s 2 2p 6 3s 2 3p 5 You can abbreviate the first 10 electrons with a noble gas, Neon. [Ne] replaces 1s 2 2s 2 2p 6 The next energy level after Neon is 3 So you start at level 3 on the diagonal rule (all levels start with s) and finish the configuration by adding 7 more electrons to bring the total to 17 [Ne] 3s 2 3p 5

 Write the shorthand notation for each of the following atoms: Cl K Ca I Bi

 Write the symbol of the noble gas before the element  Then the rest of the electrons.  Aluminum - full configuration  1s 2 2s 2 2p 6 3s 2 3p 1  Ne is 1s 2 2s 2 2p 6  so Al is [Ne] 3s 2 3p 1

Sn- 50 electrons The noble gas before it is Kr [ Kr ] Takes care of 36 Next 5s 2 5s 2 Then 4d 10 4d 10 Finally 5p 2 5p 2 [ Kr ]5s 2 4d 10 5p 2