Chapter 4b_electronic Atomic Structure

CHAPTER 4

Electronic Structure of Atom Electron Configuration

1

Summary

:

(Previous Lecture)

Principal Quantum Number, n Indicates main energy levels n = 1, 2, 3, 4… Each main energy level has sub-levels

Energy Sublevels

s

p

d

f

g

Summary

:

(Previous Lecture)

The principle quantum number, n, determines the number of sublevels within the principle energy level.

Summary

:

(Previous Lecture)

Orbital Quantum Number, ℓ (Angular Momentum Quantum Number) Indicates shape of orbital sublevels

ℓ = n-1 ℓ sublevel 0 1 2 3 4

s p d f g

Summary

:

(Previous Lecture)

Orbital The space where there is a high probability that it is occupied by a pair of electrons. Orbitals are solutions of Schrodinger’s equations.

Summary

:

(Previous Lecture)

Orbitals in Sublevels Sublevel # Orbitals s 1 p 3 d 5 f 7 g 9

# electrons 2 6 10 14 18

Summary

:

(Previous Lecture)

Shell – electrons with the same value of n Subshell – electrons with the same values of n and l Orbital – electrons with the same values of n, l, and ml

How many electrons can an orbital hold? If n, l, and ml are fixed, then ms = ½ or - ½

Ψ = (n, l, ml, ½or ) Ψ = (n, l, ml, -½) An orbital can hold 2 electrons

7.6

How many 2p orbitals are there in an atom? n=2 If l = 1, then ml = -1, 0, or +1 2p

3 orbitals

l=1

How many electrons can be placed in the 3d subshell?

n=3 3d l=2

If l = 2, then ml = -2, -1, 0, +1, or +2 5 orbitals which can hold a total of 10 e-

7.6

Electron Configuration The way electrons are arranged around the nucleus. Three rules are used to build the electron configuration:   

Aufbau’s principle Pauli Exclusion Principle Hund’s Rule 9

Aufbau’s Principle Electrons occupy orbitals of lower energy first.

Aufbau Diagra m

Energy of orbitals in a single electron atom Energy only depends on principal quantum number n

n=3 n=2

En = -RH(

1 n2

)

n=1 7.7

Energy of orbitals in a multi-electron atom Energy depends on n and l

n=3 l = 2 n=3 l = 0 n=2 l = 0

n=3 l = 1 n=2 l = 1

n=1 l = 0 7.7

“Fill up” electrons in lowest energy orbitals (Aufbau principle)

? ? Li Be B C5 6 34electrons electrons 2 222 12 1 BBe Li1s1s 1s 2s2s 2s 2p

H He1 2electron electrons He H 1s 1s12

7.7

Pauli Exclusion Principle (Wolfgang Pauli, Austria, 1900-1958) -Electron Spin Quantum Number

auli exclusion principle - no two electrons in an atom can have the same four quantum numbers.

An orbital can hold only two electrons and they must have opposite spin.

Electron Spin Quantum Number (ms): +1/2, -1/2

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

Aufbau Diagram for Hydrogen

Aufbau Diagram for Helium

Aufbau Diagram for Lithium

Aufbau Diagram for Beryllium

Aufbau Diagram for Boron

Aufbau Diagram for Carbon

Aufbau Diagram for Nitrogen

Order of orbitals (filling) in multi-electron atom

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s

7.7

Notations of Electron Configurations Standard Shorthand

Aufbau Diagram for Fluorine

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

of Fluorine

1s 2s 2p 2

y g r e n E n i l Ma Leve s r e b m Nu , 2, 2 1

2

5

Sublevels

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

Periodic Table

8.2

Outermost subshell being filled with electro

7.8

Paramagnetic unpaired electrons

2p

Diamagnetic all electrons paired

2p

7.8

The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule).

N F O C Ne 96 7 8 10 electrons electrons electrons 2 222 5 Ne N O C F 1s 1s 1s222s 2s 2s2p 2p 2p2346

7.7

What is the electron configuration of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s22s22p63s2

2 + 2 + 6 + 2 = 12 electrons

Abbreviated as [Ne]3s2

[Ne] 1s22s22p6

What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s22s22p63s23p5

1s < 2s < 2p < 3s < 3p < 4s 2 + 2 + 6 + 2 + 5 = 17 electrons

Last electron added to 3p orbital n=3

l=1

ml = -1, 0, or +1

ms = ½ or -½

7.7