Honors ChemistrySection 4.3

Electron Configurations

Electron Configuration

Electron Configuration is the arrangement of electrons in an atom

Every atom has a unique electron configuration

Atoms tend to lowest E state, so normally exist in ground state

Rules for Electron Configuration

Aufbau Principle – Electrons occupy the lowest energy orbital available to them

Pauli Exclusion Principle – No two electrons can have the same 4 quantum numbers

Hund’s Rule – Orbitals of equal energy (called degenerate orbitals) are each occupied by one electron, before any is occupied by a second electron. All single electrons have the same spin.

Orbital Energies

Orbital Notation

Hydrogen◦ ↿

1s

Helium◦ ↿⇂

1s

Oxygen◦ ↿⇂ ↿⇂ ↿⇂ ↿⇂ ↿⇂ 1s 2s 2px 2py 2pz

Electron Configuration

Hydrogen◦1s1

Helium◦1s2

Oxygen◦1s2 2s2 2p4

Filling Order – Memory Aid

Practice

What is the electron configuration of Carbon?

Write the electron configuration and orbital notation for Sulfur

Definitions

Highest Occupied Level – The highest main energy level (highest n value) that contains an electron

Outer shell electrons – electrons in the Highest Occupied Level

Inner shell electrons – all those electrons EXCEPT those in the Highest Occupied Level

Example – Carbon◦2 inner shell electrons◦4 outer shell electrons

Noble Gases

Noble gas – Has full s and p orbitalsNoble gas configuration

◦[symbol] stand for the complete electron configuration of the specified noble gas

◦Add electrons after noble gas required for element.

◦Na – [Ne] 3s1

Important Note

All noble gases have full outer main energy levels◦He – 2 electrons (Energy Level n=1)◦All others – 8 electrons (Energy Level n = 2 to

7)

Filling Orbtials and the Periodic Table

Fourth Period

Fill 4s firstThen next lowest energy 3d – it fills nextFollowed by 4p

4th Period Exceptions to the Expected Filling Order – KNOW THESE!!!!

Chromium◦Expected - [Ar] 3d4 4s2

◦Actual - [Ar] 3d5 4s1

◦Why? Two half filled orbitals have more stability and lower energy

than one full and one partially fullCopper

◦Expected - [Ar] 3d8 4s2

◦Actual - [Ar] 3d10 4s0

◦Why? A full d orbital and unfilled s orbital have more stability and

lower energy than one full and one partially full

5th Block Exceptions to the Expected Filling Order

Deviates from Nb to Ag

Practice

1. What element has 2 electrons in the p orbitals in the 2nd Energy Level?

2. What is the maximum number of electrons that can be found on the second energy level?

3. What element in the third period has the same outer electron configuration as the element in #1?

More Practice

1. What element has 5 electrons in the p sublevel on the third energy level?

2. How many total electrons does this element have on the third energy level?

3. What element in the 4th Period has the same outer configuration as this element?

Even More Practice

What element has the configuration [Ne]3s1?

How many inner shell electrons does this element have?

What is the Noble Gas configuration for Al?◦How many outer shell electrons?◦How many inner shell electrons?

Are you Ready for More?

Write the electron configuration and Noble Gas configuration for Ti.

How many electron containing orbitals in Ti?

How many orbitals in Ti are completely filled?