ELECTRON CONFIGURATIO

N

What is Electron Configuration

  The electron configuration of an atom is a form of notation which shows how the electrons are distributed among the various atomic orbital and energy levels.  The format consists of a series of numbers, letters and superscripts.

Example

1s2

1s2- HeliumThis electron configuration provides us with

the following information: The large number "1" refers to the principle quantum number

"n" which stands for the energy level.  It tells us that the electrons of helium occupy the first energy level of the atom.

The letter "s" stands for the angular momentum quantum number "l".  It tells us that the two electrons of the helium electron occupy an "s" or spherical orbital.

The exponent "2" refers to the total number of electrons in that orbital or sub-shell.  In this case, we know that there are two electrons in the spherical orbital at the first energy level.

Principle Quantum Number (n) and Sublevels

The number of sublevels that an energy level can contain is equal to the principle quantum number of that level.  So, for example, the second energy level would have two sublevels, and the third energy level would have three sublevels. 

First Sublevel

is called an s sublevel

The second sublevel

is called a p sublevel. 

The third sublevel

is called a d sublevel

The fourth sublevel

is called an f sublevel. 

What about more ?

Although energy levels that are higher than 4 would contain additional sublevels, these sublevels have not been named because no known atom in its ground state would have electrons that occupy them.

Sub-Energy Levels

Energy Level

Number of sublevels

Names of sublevels

1 1 s

2 2 s, p

3 3 s, p, d

4 4 s, p, d, f

5 5 s, p, d, f, g

SUBLEVELS AND

ORBITALS

SublevelEach type of sublevel

holds a different number of orbitals, and

therefore, a different number of electrons. 

ORBITAL

Space occupied by a pair of electrons

How many electrons the sublevels can

hold? s sublevels have one orbital, which can hold up to two electrons.

p sublevels have three orbitals, each of which can hold 2 electrons, for a total of 6.

d sublevels have 5 orbitals, for a possible total of 10 electrons.

f sublevels, with 7 orbitals, can hold up to 14 electrons. 

Orbital and Electron Capacity for the Four Named Sublevels

Sublevel # of orbitalsMaximum number of electrons

s 12

p 36

d 510

f 714

Total Number of Orbital and Electrons per Energy Level

An easy way to calculate the number of orbitals found in an energy level is to use the formula n2. 

For example, the third energy level (n=3) has a total of 32, or nine orbitals. 

This makes sense because we know that the third energy level would have 3 sublevels;

an s sublevel with one orbital, a p sublevel with 3 orbitals and a d sublevel with 5 orbitals.  1 + 3 + 5 = 9, so the formula n2 works!

Total Number of Electrons per Energy Level

An easy way to calculate the total number of electrons that can be held by a given energy level is to use the formula 2n2.  

For example, the fourth energy level (n=4) can hold 2(4)2 = 32 electrons. 

This makes sense because the fourth energy level would have four sublevels, one of each of the named types. 

The s sublevel hold 2 electrons, the p sublevel holds 6 electrons , the d sublevel holds 10 electrons and the f sublevel holds 14 electrons.  2 + 6 + 10 + 14 = 32, so the formula 2n2 works! 

Write a mathematical equation that allows us to predict the Max # if we know the energy level (n)

ENERGY LEVEL MAX # OF ELECTRONS

1 22 83 184 325 50

Max # = …n…

Equation to calculate Max # of e-

2n2

Where n is any energy level

ELECTRON CONFIGURATION

A detailed way of showing the order in which electrons fill in

around the nucleus

K

K:

2s21s2

4s1

3s2

2p6

3p6

Bohr Models vs. e- Config

s

ELECTRON CONFIGURATION SYMBOLS

5f 3

Energy Level

Sub-Energy Level

# of e- in sub-

energy level

Standard Notation of Fluorine

Main Energy

Level

Numbers

1, 2, 2Sublevels

Number of electrons in the sub level 2,2,5

1s2 2s2 2p5

Blocks in the Periodic Table

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] 2s2 2p5

The Pauli Exclusion Principle

In 1925, Wolfgang Pauli stated: No two electrons in an atom can have the same set of four quantum numbers. This means no atomic orbital can contain more than TWO electrons and the electrons must be of opposite spin if they are to form a pair within an orbital.

Hund’s RuleThe most stable arrangement of

electrons is one with the maximum number of unpaired electrons. It minimizes electron-electron repulsions and stabilizes the atom.

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).

AnalogyIn large families with several children, it is a luxury for each child to have their own room.

There is less fussing and fighting if siblings are not

forced to share living quarters. The entire household

experiences a lower, less frazzled energy state.

Electrons find each other very repulsive, so they too, are in a

lower energy state if each “gets their own room” or in

this case orbital.

Electrons that are single occupants of orbitals have parallel (same

direction) spins and are assigned an up arrow.

Analogy: Students could fill each seat of a school bus, one person at a time, before doubling up.

The second electron to enter the orbital, thus forming an electron pair, is assigned a down arrow to

represent opposite spin.

Orbital notation is basically just another way of expressing the electron configuration

of an atom.

-Electron Spin Quantum Number

An orbital can hold only two electrons and they must have

opposite spin.

Orbital Notation for Three Noble Gases

Aufbau Diagram

for Hydrogen

Aufbau Diagram for

Helium

Aufbau Diagram for

Lithium

Aufbau Diagram for Beryllium

Aufbau Diagram for

Boron

Aufbau Diagram for

Fluorine