Section 5.3

Ground State Electron ConfigurationsReview from Section #2:According to the quantum mechanical model of the atom…

Principle Energy Level (n)

Energy Sublevel

Orbitals

s, p, d, f, …

2 e-s per orbital

Ground State Electron ConfigurationsThe arrangement of e-s in an atom is called the atom’s

electron configuration.The ground state is the “normal” electron configuration of

the atom…but why?The atom wants to be in a state that is as low in energy as

possible. I guess that means that atom’s are lazy???

Atoms are the most stable when they are in their lowest energy state.

Ground State Electron ConfigurationsThe Aufbau Principle

Aufbau (in German) = “building up” or “construction

The aufbau principle states that each e occupies the lowest energy orbital available.

Ground State Electron ConfigurationsThe Aufbau Principle – Statements:

All orbitals within a specific sublevel are equal in energy.The energy sublevels contained within a single principle

energy level have different energies.Sublevels in order of increasing energy: s, p, d, fFor related sublevels, the one with the higher principle

quantum # is higher in energy.

Ground State Electron ConfigurationsThe Aufbau Principle – Statements:

All orbitals within a specific sublevel are equal in energy. Example: All 2p orbitals are equal in energy

The energy sublevels contained within a single principle energy level have different energies. For n=2, the p sublevel is higher in energy than the s sublevel

Sublevels in order of increasing energy: s, p, d, fFor related sublevels, the one with the higher principle

quantum # is higher in energy. The 3p sublevel is higher in energy than the 2p sublevel

Ground State Electron ConfigurationsThe Pauli Exclusion Principle:Electrons have a property known as spin…an electron can

have an up spin or a down spin.The Pauli exclusion principle states that only 2 e-s can

occupy an orbital at one time and that the e-s must have opposite spin to share the same orbital!

Ground State Electron ConfigurationsHund’s Rule:

Hund’s “Hungry” RuleWithin an energy sublevel, each orbital must receive

one electron before any orbital receives a 2nd electron.

Yum, Yum!!!

Orbital DiagramsThere are two major ways to represent an atom’s

electron configuration: orbital diagrams and electron configuration notation.

In the orbital diagram method, an empty box represents an orbital.

Orbital Diagrams

Li

Be

B

Orbital Diagrams

C

N

F

Orbital Diagrams

Si

Electron Configuration NotationThe electron configuration method uses the principle

energy levels and the sublevel names in writing the notation. The number of electrons in each sublevel is indicated with a superscript above the sublevel symbol.

Orbital Diagrams e- configuration notation

orbitals sublevels

Electron Configuration NotationHow can you decide on the order to fill all of the

orbitals? The diagram below can help you! (Hint: Follow the arrows)

Electron Configuration NotationHomework: Practice Problems #18, 19, 20 (p.139)

Section Assessment #24, 26 (p.141)

Electron Configuration NotationWhy are the electron sublevels arranged in a non-

numerical order? In particular, look at the last two arrows in the diagram below:

Electron Configuration NotationRemember…electrons will stay in the lowest energy orbital that is available to them!!!

Electron Configuration Notation

Electron Configuration Notation

Shorthand Electron Configuration NotationWhat is the election configuration notation for…

Argon (Ar)

Potassium (K)

Shorthand Electron Configuration NotationPutting the noble gas in brackets [ ] indicates that the

atom of interest contains the same e- configuration up until that point!

Electron Configuration NotationOne last note about writing electron configurations…

you will not always be able to use the “cheat sheet” that you have.

Electron Configuration NotationBut never fear, there is a way for you to get help! You

can use…the periodic table!!!

Electron Configuration Notation

Electron Configuration Notation

Valence ElectronsThe chemistry of elements only depends on the e-s in

the outermost principle energy level.This level or “shell” of e-s are known as valence

electrons.Using the shorthand e- configuration notation, it is

incredibly easy to identify the valence electrons for an atom.

Valence Electrons

Valence Electrons

Valence ElectronsFirst, let’s get some more practice writing out electron

configurations…write out the following elements using both the long and shorthand method:

Copper – Cu

Promethium – Pu

Uranium – U

Valence ElectronsAn atom can have anywhere between 1 and 8 valence

e-s.Why? Only the outermost s and p orbitals matter when

counting valence electrons!!!

How many valence electrons are in the following atoms, according to their electron configurations?FrBrSb

Electron Dot StructuresAs stated earlier, valence e-s are involved in the

formation of chemical bonds. Therefore, it is useful to have a visual, shorthand way of representing the valence e-s.

An electron-dot structure is made up of the element’s chemical symbol surrounded by dots that represent the valence electrons.

See page 140 for lots of examples!!!

Electron Dot StructuresRule: You must give each side of the chemical symbol

one electron before any side gets two.

Electron Dot Structure Examples:

Carbon Arsenic Iodine

Krypton

Electron Configuration Notation

Homework (11/4):Practice Problems p. 139: #18d,e (can use shorthand!)

21,22

Practice Problems p. 141: #23a,b,c

Section Assessment p. 141: #24,26,28

Homework (11/5):Practice Problems p. 141: #23a,b,c,d,f

Section Assessment p. 141: #25 (e- configuration only), 28