chapter 4b_electronic atomic structure

8/14/2019 Chapter 4b_electronic Atomic Structure

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CHAPTER4

Electronic Structure ofAtom

Electron ConfigurationElectron Configuration


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SummarySummary

(Previous Lecture)(Previous Lecture)::

Indicates main energy levels

n = 1, 2, 3, 4

Each main energy level has sub-levels

Principal Quantum Number, nPrincipal Quantum Number, n

Energy SublevelsEnergy Sublevels

s p d f g


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The principle quantum number, n, determinesthe number of sublevels within the principleenergy level.

SummarySummary



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Orbital Quantum Number, Orbital Quantum Number, (Angular Momentum Quantum Number)(Angular Momentum Quantum Number)

Indicates shape of orbital sublevels

= n-1 sublevel

0 s

1 p

2 d

3 f

4 g

SummarySummary



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OrbitalOrbital

The space where there is a high

probability that it is occupied bya pair of electrons.

Orbitals are solutions ofSchrodingers equations.

SummarySummary



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Orbitals in SublevelsOrbitals in Sublevels

Sublevel # Orbitals # electrons

s 1 2

p 3 6

d 5 10

f 7 14

g 9 18

SummarySummary



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Shell electrons with the same value ofn

Subshell electrons with the same values ofnandl

Orbital electrons with the same values ofn, l, andml

How many electrons can an orbital hold?

Ifn, l, and mlare fixed, then m

s= or -

= (n, l, ml, )or = (n, l, ml, -)

An orbital can hold 2 electrons 7.6

SummarySummary(Previous Lecture)(Previous Lecture)::


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How many 2p orbitals are there in an atom?

2p

n=2

l = 1

Ifl = 1, then ml = -1, 0, or +1

3 orbitals

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

3d

n=3

l = 2

Ifl = 2, then ml = -2, -1, 0, +1, or +2

5 orbitals which can hold a total of 10 e-

7.6


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Electron ConfigurationElectron Configuration

The way electrons are arrangedaround the nucleus.

Three rules are used to build theelectron configuration:

Aufbaus principle

Pauli Exclusion Principle

Hunds Rule


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Aufbaus PrincipleAufbaus Principle

Electrons occupy orbitals of lower energy first.


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Diagram


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nergy of orbitals in anergy of orbitals in a singlesingle electron atomelectron atomEnergy only depends on principal quantum number n

En = -RH( )1

n2

n=1

n=2

n=3

7.7


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Energy of orbitals in a multi-electron atom

Energy depends on n and l

n=1 l = 0

n=2 l = 0n=2 l = 1

n=3 l = 0n=3 l = 1

n=3 l = 2

7.7


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Fill up electrons in lowest energy orbitals (Aufbau principle)

H 1 electron

H 1s1

He 2 electrons

He 1s2

Li 3 electrons

Li 1s22s1

Be 4 electrons

Be 1s22s2

B 5 electrons

B 1s22s22p1

C 6 electrons

? ?

7.7


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Pauli Exclusion Principle(Wolfgang Pauli, Austria, 1900-1958)

-Electron Spin Quantum Number

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

Electron Spin Quantum Number (ms):

+1/2, -1/2

uli exclusion principle - no two electrons in an atocan have the same four quantum numbers.


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Hunds Rule

In a set of orbitals, the electrons will fillthe orbitals in a way that would givethe maximum number of parallel spins

(maximum number of unpairedelectrons).

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


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Aufbau

DiagramforHydrogen


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Aufbau

Diagramfor

Helium


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AufbauDiagram

forLithium


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Aufbau

Diagramfor Boron


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AufbauDiagram

forCarbon


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d f bi l (filli ) i l i l


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Order of orbitals (filling) in multi-electron atom

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

7.7


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Notations of ElectronNotations of Electron

ConfigurationsConfigurations

Standard

Shorthand


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AufbauDiagram

forFluorine

Standard Notation


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Standard Notation

of Fluorine

MainE

nergy

Level

Numbers

1,2,2 Sublevels

Number of electrons

in the sub level 2,2,5

1s2 2s2 2p5


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Shorthand Notation

Use the last noble gas that islocated in the periodic table rightbefore the element.

Write the symbol of the noble gasin brackets.

Write the remaining configuration

after the brackets.Ex: Fluorine: [He] 2s2 2p5


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8.2

Periodic Table

O b h ll b i fill d i h l


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Outermost subshell being filled with electrOutermost subshell being filled with electr

7.8


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Paramagnetic

unpaired electrons

2p

Diamagnetic

all electrons paired

2p

7.8


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C 6 electrons

The most stable arrangement ofelectrons in subshells is the one with

the greatest number of parallel spins(Hunds rule).

C 1s22s22p2

N 7 electrons

N 1s22s22p3

O 8 electrons

O 1s22s22p4

F 9 electrons

F 1s22s22p5

Ne 10 electrons

Ne 1s22s22p6

7.7


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What is the electron configuration of Mg?

Mg 12 electrons

1s < 2s < 2p < 3s < 3p < 4s

1s22s22p63s2 2 + 2 + 6 + 2 = 12 electrons

7.7

Abbreviated as [Ne]3s2 [Ne] 1s22s22p6

What are the possible quantum numbers for the last(outermost) electron in Cl?

Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s

1s22s22p63s23p5 2 + 2 + 6 + 2 + 5 = 17 electrons

Last electron added to 3p orbital

n = 3 l = 1 ml

= -1, 0, or +1 ms

= or -


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chapter 4b_electronic atomic structure

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