Electron configurations

According to the Wave – Mechanical Model

Definition

• Shows the arrangement of electrons in the atom

Sublevels of PELS

1. within an energy level, orbitals with different shapes occupy different regions, known as sublevels

2. the # of the principal energy level will identify the possible number of sublevels

3. first 4 assigned are the s, p, d, and f

S - sublevel

a. s sublevels have the lowest energy

b. contains one orbitalc. each orbital can hold a

max of 2 e-

d. has spherical shape

P sublevels

a. contains 3 orbitals b. Max of 6 e-, along 3 axisc. has peanut shape

D Sublevel

a. contains 5 orbitals b. has double peanut

shape

F sublevel

a. contain 7 orbitalsb. Has most energy of all sublevels

Chart of PELs and sublevelsPEL Sublevel # orbitals # electrons

1

2

3

4

The Rules for Electron Configurations• Aufbau principle – an electron occupies the lowest

energy orbital that can receive itFill order:

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

The Aufbau principle helps us to determine the electron configuration of atoms.

• Write the electron configuration of an atom of Beryllium (Be)

1. Identify the number of electrons in the atom.

Ex) ________

2. Begin to place electrons in the sublevels, by writing the number of electrons that will fit in each sublevel for that atom.

Ex) _____________________

1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f

Subtract the number of electrons that have been placed in the sublevel from the total number of electrons in the atom (this will tell you how many electrons you have leftover). Continue placing electrons in sublevels, following the fill order, until you run out of electrons for that atom.

Ex) _____________________

Configurations and the Periodic Table

Orbital Notation

• graphically represents the arrangement of electrons in their energy levels & sublevels

• Hund’s rule : electrons occupying the same orbital must have opposite spins (we’ll show that with arrows), and electrons will fill one electron per orbital (with identical spin) in a sublevel before they double up.

Write the electron configuration for N.

1s22s22p3

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for Ne

1s22s22p6

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for O

1s22s22p4

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for Ti

1s22s22p63s23p64s23d2

3d ______ ______ ______ ______ ______

4s ______3p ______ ______ ______3s ______2p ______ ______ ______

2s ______

1s ______

Valence ElectronsDefinition: electrons that occupy the outermost PEL

of an atom

- Maximum number of valence electrons is 8Reason: result of full s and p sublevels

- energy levels (clouds) begin to overlap from the 3rd to the 4th energy level

How many valence electrons are there in the following:

Sodium: ________ Argon: ________

Oxygen: ________ Magnesium: ______

Carbon: ________ Strontium: ______

IonsDefinition: Electrically charged atoms (unequal

# of protons and electrons)- formed when atoms lose or gain electrons- in order to have a complete valence energy level (stable configuration)

- Possible charges are listed on the Periodic Table

CationsDef: a positively charged ion

- Formed when atoms lose electrons

Ex) Sodium atom Sodium ion (Na+1)

Sodium ion configuration same as Neon

AnionsDef: negatively charged ions

- Formed when atoms gain electrons

Ex) Fluorine atom Fluoride ion (F-1)

Fluoride ion configuration same as Neon