Electron Configuration and Lewis Dot StructuresUnit 5

Atomic OrbitalsEnergy levels (shells) = nn = 1, 2, 3.etc.The higher the energy level, the farther away from the nucleusSublevelsDesignated by s, p, d, fRefers to the shape (s) of the area in which the electron can be locatedAlso designates an energy level within the shellRepresents the region in space where the electron is most likely to be show 90% probabilityCloud is more dense where probability of finding an e- is highWhere are the e- within each sublevel?We dont know! Cant determine the exact position of an e- in an atom

Atomic Orbitals cont.Denoted by letters indicate shapes orbitals sphere shapedCan accommodate 2 electronsp orbitals dumbbell shapedCan accommodate 6 electronsd orbitals more complex; flower shaped or double dumbbellsCan accommodate 10 electronsf orbitals even more complex; wont cover shapesCan accommodate 14 electronsRelative energy: s < p < d < f

xyzp subshell: pair of lobes

s subshell: spherical1 orbital

Electron Configurations

Def: the ways in which electrons are arranged around the nucleus of an atomShow the approximate location of electronsRepresent in which orbitals electrons are located

Electron Configurations cont.Aufbau Principle Electron configuration determined since electrons tend to be in lowest energy orbitals.Rules:The Aufbau principle (building up) guides us in the filling of orbitals:Fill lowest energies first.Maximum of two electrons with opposite spins in each orbital. (Paulis Exclusion Principle)Degenerate orbitals (orbitals with same energy) follow Hunds rule

Electron Configurations cont.Hunds RuleHunds rule: If two or more orbitals have the same energy, fill each orbital with one electron before pairing electrons.

Periodic Table and Electron ConfigurationsBuild-up order given by position on periodic table; row by row.Elements in same column will have the same outer shell electron configuration.

Electron Configurations cont.

1st shell has 1 subshell (s)Holds maximum of 2 electrons

HydrogenHelium1senergy1 s11 s21s

Electron Configuration cont.Electron Configuration for Li (Z=3)1s2nd shell2s2p 2s

Li 1s Orbital Energy Level DiagramLi 1s22s1Electronic configuration

Electron Configuration cont.Electron Configuration for Boron (Z = 5)1s2nd shell2s2pBe 1s22s2 2s

Be 1s 1s2nd shell2s2pB 1s22s22p1 2p 2s

B 1s

D Subshellxyxzxyyzz2x2-y2

ExamplesFill according to the Energy Level DiagramEx:C1s22s22p2Ne1s22s22p6Na1s22s22p63s1

Short Hand (Nobel Gas) Notation Show electron filling starting from previous noble gas.Know how electron configurations work on the periodic table.Ex P: [Ne] 3s23p3Your Turn:NMgCaCu

Electron Dot Diagrams (aka Lewis Dot Structures)How do we draw a picture for the number of electrons an atom has? If you want to see how atoms of one element will react, it is handy to have an easier way to represent the atoms and the electrons in their outer energy levels. You can do this with electron dot diagrams.An electric dot diagram is the symbol for the element surrounded by as many dots as there are electrons in its outer energy level.

How to Write E.D.D.sThe dots are written in pairs on four sides of the element symbol. Start by writing one dot on the top of the element symbol, then work your way around adding dots to the right, bottom, and left.

How to Write E.D.D.sAdd a fifth dot to the top to make a pair. Continue in this manner until you reach eight dots to complete the level.

QUESTIONThe _______ an energy level is from the nucleus, the _______ electrons it can hold.A. closer, moreB. closer, lessC. farther, lessD. farther, more

ANSWER

The answer is D. The farthest shells contain the greatest number of electrons.