5.3 – Electron Configurations

• OBJECTIVES: Students will be able to (SWBAT)

1. Draw orbital diagrams of the electron configuration of

atoms

2. Write electron configuration notations for atoms2. Write electron configuration notations for atoms

• 5 lecture Q’s

• 5-sentence summary (combine with 5.2 and

reading)

Notes: Electron Configurations

(5.3)

Ground State Electron Configuration

• Electrons in an atom will arrange themselves

to give the atom the lowest possible energy

(most stable) � ground state electron

configuration (arrangement)configuration (arrangement)

Ruling Principles of Electron Arrangement

• 3 major priniciples:

– Aufbau Principle – electrons fill lowest energy

levels first.

– Pauli Exclusion Principle – only 2 electrons can – Pauli Exclusion Principle – only 2 electrons can

occupy an orbital and must have opposite spins

(means they move in opposite directions)

– Hund’s Rule – electrons fill the orbitals of an

energy level with the same spin first then the

opposite spin.

Orbital Filling Sequence Diagram

• Diagram

– Lowest energy level on the bottom (1st, 2nd, 3rd

and so on)

• s sublevels first, then p, then d, then f• s sublevels first, then p, then d, then f

• Boxes represent an orbital

Electrons as Arrows on the Diagram

• Arrows (↑, ↓) represent electrons with

different spins

Orbital Filling Sequence Diagram

Energy Level Overlap

•d sublevels of a

level actually

come after the s

sublevel of the sublevel of the

next level

- For example,

3d will come

after 4s

Orbital Diagrams and Electron

Configuration Notation

• Filling sequence:

Pauli’s principle: each orbital can hold 2 e-

s �1 orbital � can hold 2 e-s �1 orbital � can hold 2 e-

p � 3 orbitals � total of 6 e-

d � 5 orbitals � total of 10 e-

f � 7 orbitals � total of 14 e-

Sublevel and Orbital Order

1s2

1s22s22p61s 2s 2p

How to Write Noble Gas Configuration

1) Use the LAST column of elements only (the

noble gases) in the brackets [ ]

2) Continue with the next row (starting always

with s orbitals, then d (if needed), then pwith s orbitals, then d (if needed), then p

3) Always use the closest previous noble gas for

the short-cut

Electron Configuration (e- config) Notation

• e- config notation is another way to show electron

arrangement in an atom

• Use orbital diagrams to help write e- config notations

• Write the number of electrons in each orbital as

superscriptssuperscripts

• Long-hand notation: ALL orbitals are written out with

number of electrons

• If all superscripts in the notation are added, it should

add up to the total number of electrons in the atom

2+2+4 = 8 electrons

How to Write Noble Gas Configuration –

Short-hand Notation

• Uses noble gas e-config notation to abbreviate

longer notations

1) Noble gas element is written in brackets [ ]

2) Use the noble gas (the ones in the last column) 2) Use the noble gas (the ones in the last column)

immediately before the element for which you’re

writing the notation

3) Write the remaining orbitals after the noble gas

until you reach the appropriate number of

electrons

1s2

1s22s22p61s 2s 2p

Examples

• Kr: 1s22s22p63s23p64s23d104p6

• Sr: 1s22s22p63s23p64s23d104p6 5s2[Kr]

Practice

• In your blank orbital diagram worksheet,

complete one diagram for selenium (Se).