Copyright Sautter 2003

ELECTRONIC CONFIGURATION OF ATOMS

USING ENERGY LEVEL DIAGRAMS

FOR

ATOMS

&

IONS

WHAT IS AN ELECTRONIC CONFIGURATION?

• ELECTRONIC CONFIGURATIONS SHOW THE ENERGY STATES (ARRANGEMENTS) OF ELECTRONS WITHIN DIFFERENT ATOMS

• FOR EXAMPLE WE CAN DETERMINE FROM THE PERIODIC TABLE THAT HYDROGEN ATOMS (ATOMIC NUMBER =1) HAVE BUT ONE ELECTRON WHILE OXYGEN (ATOMIC NUMBER = 8) HAS EIGHT ELECTRONS, BUT HOW ARE THEY ARRANGED WITH EACH ATOM?

DETERMINING ELECTRON CONFIGURATIONS

• IN ORDER WRITE A CORRECT CONFIGURATION FOR AN ATOM WE MUST:

• (1) FIND THE NUMBER OF ELECTRONS THE ATOM CONTAINS

• (2) USE THE ENERGY LEVEL DIAGRAM TO DETERMINE THE ORBITIAL LOCATIONS OF THE ELECTRONS

• (3) PLACE THE ELECTRONS IN THE PROPER ORBITALS USING TWO FUNDAMENTAL RULES (THE PAULI EXCLUSION PRINCIPLE AND HUND’S RULE)

ORDER OF

ENERGY LEVEL

FILLING

DETERMINING ELECTRON CONFIGURATIONS (CONT’D)

• THE PAULI EXCLUSION PRINCIPLE STATES THAT A MAXIMUM OF TWO ELECTRONS (EACH WITH OPPOSITE SPINS) MAY OCCUPY AN ORBITAL

• HUND’S RULE STATES THAT ORBITALS OF EQUAL ENERGY MUST BE FILLED WITH ELECTRONS ONE AT A TIME UNTIL ALL OF THE ORBITALS ARE HALF FILLED, THEN FILLING MAY BE COMPLETED RESULTING IN EACH ORBITAL CONTAINING TWO ELECTRONS MAXIMUM

DETERMINING ELECTRONCONFIGURATIONS (CONT’D)

• ELECTRONS ARE ADDED TO THE ENERGY LEVEL DIAGRAM ACCORDING TO THE RULES PREVIOUSLY OUTLINED USING AN ARROW TO REPRESENT EACH ELECTRON.

• EACH ORBITAL MAY CONTAIN A MAXIMUM OF TWO ARROWS, ONE POINTED UPWARD AND ONE POINTED DOWNWARD TO SHOW THE OPPOSITE SPINS OF THE PAIRED ELECTRONS.

• NOW LET’S SHOW THE ELECTRON CONFIGURATION FOR THE HYDROGEN ATOM.

Electronic Configuration

For Hydrogen (1 electron)

Energy LevelNumber

OrbitalType

Number ofElectrons inthe Orbital

DESCRIBING ELECTRON CONFIGURATIONS OF ATOMS

• ELECTRON CONFIGURATIONS MAY BE REPRESENTED IN WRITTEN FORM OR DIAGRAMATIC FORM.

• IN WRITTEN FORM, THE ENERGY LEVEL NUMBER IS WRITTEN FIRST FOLLOWED BY THE ORBITAL DESIGNATION AND FINALLY THE NUMBER OF ELECTRONS PRESENT IN THE ORBITAL IS SHOWN AS A SUPERSCRIPT.

• FOR EXAMPLE, SODUIUM Na WITH 11 ELECTRONS

WOULD BE WRITTEN AS 1s2 2s2 2p6 3s1

• IN THE 1S2 TERM THE NUMBER 1 STANDS FOR THE ENERGY LEVEL, S FOR THE ORBITAL TYPE AND THE SUPERSCRIPT 2 MEANS TWO ELECTRONS ARE PRESENT

DESCRIBING ELECTRON CONFIGURATIONS OF ATOMS (CONT’D)

• A COMMONLY USED ABBREVIATION IN WRITING CONFIGURATIONS RECOGNIZES THAT ONCE AN ENERGY LEVEL HAS BEEN FILLED AND INERT GAS CONFIGURATION HAS BEEN CREATED. FOR EXAMPLE ENERGY LEVEL 1 BEING COMPLETED GIVES A CONFIGURATION FOR He, COMPLETION OF ENERGY LEVEL 2 GIVES Ne, ENERGY LEVEL 3 GIVES Ar, ETC.

• AGAIN ASSUMING Na, 1s2 2s2 2p6 3s1, THE FIRST 10 ELECTRONS (1s2 2s2 2p6) LOOK JUST LIKE NEON AND THEREFORE THE CONFIGURATION FOR SODIUM CAN BE ABBREVIATED AS [Ne] 3s1 WHERE [Ne] = 1s2 2s2 2p6.

DESCRIBING ELECTRON CONFIGURATIONS OF ATOMS (CONT’D)

• WRITING ELECTRON CONFIGURATIONS USING THE DIAGRAMATIC METHOD REQUIRES DRAWING A BOX OR CIRCLE TO FOR EACH ORBITAL AND THEN FILLING IN ARROWS REPRESENTING EACH ELECTRON PRESENT IN EACH ORBITAL.

1s2 2s2 2p2

6 ELECTRONS

USING THE ENERGY LEVEL DIAGRAMFOR HYDROGEN

3px 3py 3pz

3s

2px 2py 2pz

2s

1s1

1s

1 ELECTRON

FOR OXYGENUSING THE ENERGY LEVEL DIAGRAM

3px 3py 3pz

3s

2px 2py 2pz

2s

1s2 2s2 2p4

1s

8 ELECTRONS

USING THE ENERGY LEVEL DIAGRAMFOR TRANSITATIONAL ELEMENTS

3d

4s 3p * NOTICE 4s ORBITALS FILL

3s BEFORE 3D ORBITALS !!

2p

2s

1s2 2s2 2p6 3s23p6

1s 4s2 3d7

27 ELECTRONS

ELECTRONIC CONFIGURATIONS OF IONS• WHAT IS AN ION ?• A CHARGED ATOM OR GROUP OF ATOMS.

• HOW ARE IONS FORMED?• BY GAINING OR LOSING ELECTRONS.

• WHAT ARE THE TWO KINDS OF POSSIBLE IONS ?• POSITIVE IONS (CATIONS) AND NEGATIVE IONS (ANIONS)

• HOW ARE CATIONS AND ANIONS FORMED ?• CATIONS ARE FORMED WHEN ATOMS LOSE ELECTRONS

AND ANIONS ARE FORMED WHEN ATOMS GAIN ELECTRONS (PROTON NUMBERS NEVER CHANGE !)

ELECTRONIC CONFIGURATIONS OF IONS (CONT’D)

• WHAT TYPES OF ATOMS GENERALLY FORM CATIONS AND ANIONS ?

• CATIONS ARE GENERALLY FORMED BY METALS AND ANIONS ARE GENERALLY FORMED BY NONMETALS

• HOW CAN THE NUMBER OF ELECTRONS IN AN ION BE DETERMINED?

• FOR CATIONS, FIRST DETERMINE THE ATOMIC NUMBER OF THE ATOM. THIS IS THE NUMBER OF ELECTRONS IN A NEUTRAL (UNCHARGED) ATOM. SUBTRACT THE VALUE OF THE POSITVE CHARGE ON THE ION FROM THE ATOMIC NUMBER. THIS IS THE NUMBER OF ELECTRONS IN THE CATION.

• FOR ANIONS, FIND THE ATOMIC NUMBER AND ADD THE VALUE OF THE CHARGE ON THE ION. THIS IS THE NUMBER OF ELECTRONS IN THE ANION.

ELECTRONIC CONFIGURATIONS OF IONS (CONT’D)

• HOW MANY ELECTRONS ARE CONTAINED IN THE CATION, Mg+2 ?

• THE ATOMIC NUMBER OF MAGNESIUM IS 12. THIS MEANS THAT IT HAS 12 ELECTRONS IN THE NEUTRAL MAGNESIUM ATOM. THE ION THEREFORE HAS (12 – 2) OR 10 ELECTRONS.

• HOW MANY ELECTRONS ARE CONTAINED IN THE ANION, N –3 ?

• THE ATOMIC NUMBER OF NITROGEN IS 7. THIS MEANS THAT IT HAS 7 ELECTRONS IN THE NEUTRAL NITROGEN ATOM. THE ION THEREFORE HAS (7 + 3) OR 10 ELECTRONS.

ELECTRONIC CONFIGURATIONS OF IONS (CONT’D)

• BOTH THE MAGNESIUM CATION (Mg+2) AND THE THE NITRIDE ANION ION (N –3 ) HAVE THE SAME NUMBER OF ELECTRONS. THESE IONS ARE SAID TO BE “ISOELECTRONIC” WITH EACHOTHER AND WITH THE NEAREST INERT GAS NEON (ATOMIC NUMBER = 10)

• GENERALLY, ATOMS FORM CATIONS AND ANIONS IN ORDER TO BECOME ISOELECTRONIC WITH THE NEAREST INERT GAS. IN DOING THIS ATOMS ACHIEVE COMPLETED OUTER ENERGY LEVELS AND THIS RESULTS IN GREATER CHEMICAL STABILITY !

ELECTRONIC CONFIGURATIONS OF IONS (CONT’D)

• SOME ISOELECTRONIC ATOMS AND IONS

• NAME SOME IONS THAT ARE ISOELECTRONIC WITH NEON (Ne) ?

• N-3, O-2, F-1, Na+1, Mg+2, Al+3

• NAME SOME IONS THAT ARE ISOELECTRONIC WITH ARGON (Ar) ?

• P-3, S-2, Cl-1, K+1, Ca+2

ELECTRON CONFIGURATION FOR IONS ISOELECTRONIC WITH NEON

N-3, O-2, F-1, Na+1, Mg+2, Al+3

2p 2s 1s2 2s2 2p6

1s

THE SECOND ENERGY LEVELIS COMPLETED

ELECTRON CONFIGURATION FOR IONS ISOELECTRONIC WITH ARGON

P-3, S-2, Cl-1, K+1, Ca+2

3p

3s

2p

2s

1s2 2s2 2p6 3s23p6

1s

THE THIRD ENERGY LEVELIS COMPLETED