2.3 Electron 2.3 Electron ArrangementArrangement2.3.1 Describe the electromagnetic 2.3.1 Describe the electromagnetic

spectrumspectrum2.3.2 Distinguish between a 2.3.2 Distinguish between a

continuous spectrum and a line continuous spectrum and a line spectrumspectrum

2.3.3 Explain how the lines in the 2.3.3 Explain how the lines in the emission spectrum of hydrogen are emission spectrum of hydrogen are related to electron energy levelsrelated to electron energy levels

2.3.4 Deduce the electron 2.3.4 Deduce the electron arrangement for atoms and ions up arrangement for atoms and ions up to Z=20to Z=20

Bohr’s ModelBohr’s Model

• Why don’t the electrons fall into Why don’t the electrons fall into the nucleus?the nucleus?

• Move like planets around the sun.Move like planets around the sun.• In circular orbits at different In circular orbits at different

levels.levels.• Amounts of energy separate one Amounts of energy separate one

level from another.level from another.

Bohr postulated that:Bohr postulated that:

• Fixed energy related to the orbitFixed energy related to the orbit• Electrons cannot exist between orbitsElectrons cannot exist between orbits• The higher the energy level, the The higher the energy level, the

further it is away from the nucleusfurther it is away from the nucleus• An atom with maximum number of An atom with maximum number of

electrons in the outermost orbital electrons in the outermost orbital energy level is stable (unreactive)energy level is stable (unreactive)

• Think of Noble gasesThink of Noble gases

Radiowaves

Microwaves

Infrared .

Ultra-violet

X-Rays

GammaRays

Low energy

High energy

Low Frequency

High Frequency

Long Wavelength

Short WavelengthVisible Light

Wavelength and Wavelength and frequencyfrequency

How did he develop his How did he develop his theory?theory?

• He used mathematics to explain the visible He used mathematics to explain the visible spectrum of hydrogen gasspectrum of hydrogen gas

• Lines are associated with the fall of an Lines are associated with the fall of an excited electron back down to its ground excited electron back down to its ground state energy level.state energy level.

• http://www.mhhe.com/physsci/chemistry/esshttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swfentialchemistry/flash/linesp16.swf

The line spectrum The line spectrum

• electricity passed electricity passed through a gaseous through a gaseous element emits light element emits light at a certain at a certain wavelengthwavelength

• Can be seen when Can be seen when passed through a passed through a prismprism

• Every gas has a Every gas has a unique pattern unique pattern (color)(color)

Line spectrumLine spectrum

Continuous line spectrum

Those who are not Those who are not shocked when they first shocked when they first come across quantum come across quantum theory cannot possibly theory cannot possibly

have understood it.have understood it.

(Niels Bohr on Quantum (Niels Bohr on Quantum Physics)Physics)

Wavelengths and energyWavelengths and energy

• Understand that different Understand that different wavelengths of electromagnetic wavelengths of electromagnetic radiation have different energies.radiation have different energies.

• c=vc=vλλ– c=velocity of wave (2.998 x 10c=velocity of wave (2.998 x 1088 m/s) m/s)– v=(nu) frequency of wavev=(nu) frequency of wave– λλ=(lambda) wavelength =(lambda) wavelength

• Bohr also postulated that an Bohr also postulated that an atom would not emit radiation atom would not emit radiation while it was in one of its stable while it was in one of its stable states but rather only when it states but rather only when it made a transition between made a transition between states. states.

• The frequency of the radiation The frequency of the radiation emitted would be equal to the emitted would be equal to the difference in energy between difference in energy between those states divided by Planck's those states divided by Planck's constant. constant.

EEhighhigh-E-Elowlow= hv = hc/= hv = hc/λλ

h=3.983 x 10h=3.983 x 10-13-13 Jsmol Jsmol-1-1= Plank’s = Plank’s constantconstant

E= energy of the emitted light (photon)E= energy of the emitted light (photon)

v = frequency of the photon of lightv = frequency of the photon of lightλλ = is usually stated in nm, but for calculations = is usually stated in nm, but for calculations

use m.use m.

• This results in a unique emission spectra for This results in a unique emission spectra for each element, like a fingerprint.each element, like a fingerprint.

• electron could "jump" from one allowed energy electron could "jump" from one allowed energy state to another by absorbing/emitting photons state to another by absorbing/emitting photons of radiant energy of certain specific of radiant energy of certain specific frequencies. frequencies.

• Energy must then be absorbed in order to Energy must then be absorbed in order to "jump" to another energy state, and similarly, "jump" to another energy state, and similarly, energy must be emitted to "jump" to a lower energy must be emitted to "jump" to a lower state. state.

• The frequency, v, of this radiant energy The frequency, v, of this radiant energy corresponds exactly to the energy difference corresponds exactly to the energy difference between the two states.between the two states.

• In order for the emitted energy to be In order for the emitted energy to be seen as light the wavelength of the seen as light the wavelength of the energy must be in between 380 nm to energy must be in between 380 nm to 750 nm750 nm

For Hydrogen only!For Hydrogen only!• EEnn= -R/n= -R/n22, where R is -1312 kJ/mol and n is , where R is -1312 kJ/mol and n is

principle quantum number (energy level)principle quantum number (energy level)

• Example: Calculate the energy required to Example: Calculate the energy required to ionize a mole of electrons from the 4ionize a mole of electrons from the 4thth to to the 2the 2ndnd energy level in a hydrogen atom? energy level in a hydrogen atom?

EE44 = -1312 / 4 = -1312 / 42 2 = - 82 kJ= - 82 kJ

EE22 = -1312 / 2 = -1312 / 222 = - 328 kJ = - 328 kJ

EE44 – E – E22 = - 82 kJ – (- 328 kJ)= 246 kJ = - 82 kJ – (- 328 kJ)= 246 kJ

• What is the wavelength of light emitted What is the wavelength of light emitted when electrons go from n=4 to n=2 ? Is it when electrons go from n=4 to n=2 ? Is it visible to our eyes?visible to our eyes?

E = E = hc/hc/λλ, therefore , therefore λλ = = hc/Ehc/Eλλ = = [[(3.983 x 10(3.983 x 10-13-13 kJsmol kJsmol-1-1)()(2.998 x 102.998 x 1088 ms ms-1-1)]/(246 )]/(246

kJmolkJmol-1-1))= 4.85 x 10= 4.85 x 10-7 -7 mm

Convert to nm and see if its visible! (1 nm = 1 x 10Convert to nm and see if its visible! (1 nm = 1 x 10-9-9 m)m)

(4.85 x 10(4.85 x 10-7 -7 m)( m)( 1nm)1nm) = 485 nm (Its probably the = 485 nm (Its probably the greengreen line) line)

1 x 101 x 10-9-9 m m

Bohr’s TriumphBohr’s Triumph

• His theory helped to explain periodic His theory helped to explain periodic law (the trends from the periodic law (the trends from the periodic table)table)

• Halogens (gp.17) are so reactive Halogens (gp.17) are so reactive because it has one e- less than a full because it has one e- less than a full outer orbitalouter orbital

• Alkali metals (gp. 1) are also reactive Alkali metals (gp. 1) are also reactive because they have only one e- in because they have only one e- in outer orbitalouter orbital

DrawbackDrawback

• Bohr’s theory did Bohr’s theory did not explain or not explain or show the shape or show the shape or the path traveled the path traveled by the electrons.by the electrons.

• His theory could His theory could only explain only explain hydrogen and not hydrogen and not the more complex the more complex atomsatoms

The Quantum Mechanical The Quantum Mechanical ModelModel

• Energy is quantized. It comes in chunks.Energy is quantized. It comes in chunks.• A quanta is the amount of energy needed A quanta is the amount of energy needed

to move from one energy level to another.to move from one energy level to another.• Since the energy of an atom is never “in Since the energy of an atom is never “in

between” there must be a quantum leap between” there must be a quantum leap in energy.in energy.

• Schrödinger derived an equation that Schrödinger derived an equation that described the energy and position of the described the energy and position of the electrons in an atomelectrons in an atom

Energy level populationsEnergy level populations

• Electrons found per energy level of the atom.Electrons found per energy level of the atom.• The first energy level holds 2 electronsThe first energy level holds 2 electrons• The second energy level holds 8 electrons (2 The second energy level holds 8 electrons (2

in s and 6 in p)in s and 6 in p)• The third energy level holds 18 electrons (2 The third energy level holds 18 electrons (2

in s, 6 in p and 10 in d) There is overlapping in s, 6 in p and 10 in d) There is overlapping here, so when we do the populations there here, so when we do the populations there will be some changes.will be some changes.

That is as far as this course requires us to go!That is as far as this course requires us to go!

Examples for group 1Examples for group 1

• Li Li 2.12.1 • Na Na 2.8.12.8.1 • K K 2.8.8.12.8.8.1

A good site:A good site:http://www.chemguide.co.uk/basihttp://www.chemguide.co.uk/basicorg/bonding/orbitals.htmlcorg/bonding/orbitals.html

Electron Electron ConfigurationConfiguration

HL onlyHL only12.1.3 State the relative energies of s, p, d, and f 12.1.3 State the relative energies of s, p, d, and f orbitals in a single energy levelorbitals in a single energy level12.1.4 State the maximum number of orbitals in a 12.1.4 State the maximum number of orbitals in a given energy level.given energy level.12.1.5 Draw the shape of an s orbital and the 12.1.5 Draw the shape of an s orbital and the shapes of px, py and pz orbitalsshapes of px, py and pz orbitals12.1.6 Apply the Aufbau principle, Hund’s rule 12.1.6 Apply the Aufbau principle, Hund’s rule and the Pauli exclusion principle to write electron and the Pauli exclusion principle to write electron configurations for atoms and ions up to Z=54.configurations for atoms and ions up to Z=54.

S orbitalsS orbitals

• 1 s orbital for1 s orbital for

every energy levelevery energy level

1s 2s1s 2s 3s 3s• Spherical shapedSpherical shaped• Each s orbital can hold 2 electronsEach s orbital can hold 2 electrons• Called the 1s, 2s, 3s, etc.. orbitalsCalled the 1s, 2s, 3s, etc.. orbitals

P orbitalsP orbitals

• Start at the second energy level Start at the second energy level • 3 different directions3 different directions• 3 different shapes3 different shapes• Each orbital can hold 2 electronsEach orbital can hold 2 electrons

The D sublevel contains 5 D The D sublevel contains 5 D orbitalsorbitals• The D sublevel starts in the 3The D sublevel starts in the 3rdrd energy level energy level

• 5 different shapes (orbitals)5 different shapes (orbitals)• Each orbital can hold 2 electronsEach orbital can hold 2 electrons

The F sublevel has 7 F orbitalsThe F sublevel has 7 F orbitals• The F sublevel starts in the fourth energy levelThe F sublevel starts in the fourth energy level• The F sublevel has seven different shapes The F sublevel has seven different shapes

(orbitals)(orbitals)• 2 electrons per orbital2 electrons per orbital

SummarySummary

s

p

d

f

# of shapes (orbitals)

Max # of electrons

1 2 1

3 6 2

5 10 3

7 14 4

Sublevel

Starts at energy level

Electron ConfigurationsElectron Configurations

• The way electrons are arranged in atoms.The way electrons are arranged in atoms.• Aufbau principleAufbau principle-- electrons enter the electrons enter the

lowest energy first.lowest energy first.• This causes difficulties because of the This causes difficulties because of the

overlap of orbitals of different energies.overlap of orbitals of different energies.• Pauli Exclusion PrinciplePauli Exclusion Principle-- at most 2 at most 2

electrons per orbital - different spinselectrons per orbital - different spins• Hund’s RuleHund’s Rule-- When electrons occupy When electrons occupy

orbitals of equal energy they don’t pair up orbitals of equal energy they don’t pair up until they have to .until they have to .

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• Phosphorous, 15 e- to Phosphorous, 15 e- to placeplace

• The first to electrons The first to electrons go into the 1s orbitalgo into the 1s orbital

• Notice the opposite Notice the opposite spinsspins

• only 13 moreonly 13 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons The next electrons go into the 2s go into the 2s orbitalorbital

• only 11 moreonly 11 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 2p orbital

• only 5 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The next electrons go into the 3s orbital

• only 3 more

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

Incr

easi

ng e

nerg

y

1s

2s

3s

4s

5s6s

7s

2p

3p

4p

5p

6p

3d

4d

5d

7p 6d

4f

5f

• The last three electrons go into the 3p orbitals.

• They each go into separate shapes

• 3 unpaired electrons

• 1s22s22p63s23p3

Orbitals fill in order Orbitals fill in order • Lowest energy to higher energy.Lowest energy to higher energy.• Adding electrons can change the Adding electrons can change the

energy of the orbital.energy of the orbital.• Half filled orbitals have a lower Half filled orbitals have a lower

energy.energy.• Makes them more stable.Makes them more stable.• Changes the filling orderChanges the filling order

Write these electron Write these electron configurationsconfigurations

• Titanium - 22 electronsTitanium - 22 electrons

• 1s1s222s2s222p2p663s3s223p3p664s4s223d3d22

• Vanadium - 23 electrons Vanadium - 23 electrons 1s1s222s2s222p2p663s3s223p3p664s4s223d3d33

• Chromium - 24 electronsChromium - 24 electrons• 1s1s222s2s222p2p663s3s223p3p664s4s223d3d4 4 is expectedis expected

• But this is wrong!!But this is wrong!!

Chromium is actuallyChromium is actually• 1s1s222s2s222p2p663s3s223p3p664s4s113d3d55

• Why?Why?• This gives us two half filled orbitals.This gives us two half filled orbitals.• Slightly lower in energy.Slightly lower in energy.• The same principal applies to The same principal applies to

copper.copper.

Copper’s electron Copper’s electron configurationconfiguration

• Copper has 29 electrons so we Copper has 29 electrons so we expectexpect

• 1s1s222s2s222p2p663s3s223p3p664s4s223d3d99

• But the actual configuration isBut the actual configuration is• 1s1s222s2s222p2p663s3s223p3p664s4s113d3d1010

• This gives one filled orbital and one This gives one filled orbital and one half filled orbital.half filled orbital.

• Remember these exceptionsRemember these exceptions

Great site to Great site to practice and practice and instantly see instantly see results for results for

electron configuratelectron configurationion

..