Unit 2 – Atomic Structure Part II – Electron Configuration, EM Spectrum, & Planck’s Law.

Unit 2 – Atomic StructurePart II – Electron Configuration, EM Spectrum, & Planck’s Law

Unit 2 Part 2 Key Terms• Emission Spectrum - The range of all possible wave

frequencies of electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields

• Energy Level – discrete regions of space around the nucleus in the electron cloud where electrons can reside

• Excited state - The state of an atom when one of its electrons is in a higher energy orbital than the ground state.

• Gamma radiation - Electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength

• Ground state - The lowest energy state of an atom or other particle

Unit 2 Part 2 Key Terms (cont.)• Lewis dot structure -A model that uses electron-dot

structures to show how electrons are arranged in molecules. Pairs of dots or lines represent bonding pairs

• Noble gas configuration -An electron structure of an atom or ion in which the outer electron shell contains eight electrons, corresponding to the electron configuration of a noble gas, such as neon or argon

• Orbital notation (diagram) -A way to show how many electrons are in an orbital for a given element. They can either be shown with arrows or circles

• Planck’s constant - As frequency increases, the energy of the wave increases

Quantum Mechanical Model of Atomic Structure• 1900: Max Planck – Develops law correlating energy to

frequency of light• 1905: Albert Einstein – Postulates dual nature of light as both

energy and particles• 1924: Louis de Broglie – Applies dual nature of light to all

matter• 1927: Werner Heisenberg – Develops Uncertainty Principle

stating that it is impossible to observe both the location and momentum of an electron simultaneously

• 1933: Erwin Schrodinger – Refines the use of the equation named after him to develop the concept of electron orbitals to replace the planetary motion of the electron

Energy Levels

• Energy levels correspond to the energy of individual electrons. Each energy level has a discrete numerical value.

• Different energy levels correspond to different numbers of electrons using the formula 2n2 where “n” is the energy level

Energy Level Number of electrons (2n2)

1 2(12) = 2

2 2(22)= 8

3 2(32)= 18

4 2(42)= 32

n 2n2

OrbitalsImpossible to determine the location of any single electron

Orbitals are the regions of space in which electrons can most probably be found

Four types of orbitalss – spherically shapedp – dumbbell shapedd – cloverleaf shapedf – shape has not been determined

Each additional energy level incorporates one additional orbital type

Each type of orbital can only hold a specific number of electrons

Orbital Types

Orbital Type

General Shape

OrbitalSublevels

# of electrons

per sublevel

Total # of electrons

per orbital type

s Spherical 1 2 2

p Dumbbell 3 2 6

d Clover leaf 5 2 10

f unknown 7 2 14

Electron Configuration

Energy Level

Orbital Type

OrbitalSublevel

# of orbitals

per energy level (n2)

# of electrons

per orbital type

# of electrons

per energy level (2n2)

1 s 1 1 2 2

2sp

13

426

8

3spd

135

926

1018

4

spdf

1357

16

26

1014

32

Electron Configuration Notation

• Find the element on the periodic table• Follow through each element block in order by stating the

energy level, the orbital type, and the number of electrons per orbital type until you arrive at the element.

1s

2s     2p

3s     3p

4s   3d 4p

5s   4d 5p

6s 4f 5d 6p

7s 5f 6d 7p

Samples of e- Configuration

• Element Electron Configuration• H 1s1

• He 1s2

• Li 1s2 2s1

• C 1s2 2s2 2p2

• K 1s2 2s2 2p6 3s2 3p6 4s1

• V 1s2 2s2 2p6 3s2 3p6 4s2 3d3

• Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 (Note the overlap)• Pb 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p2

Noble Gas Electron Configuration Notation

Find element on the Periodic Table of Elements• Example: Pb for Lead

Move backward to the Noble Gas immediately preceding the elementExample: Xenon

Write symbol of the Nobel Gas in bracketsExample: [Xe]

Continue writing Electron Configuration Notation from the Noble GasExample: [Xe] 6s2 4f14 5d10 6p2

Valence Electrons

• The electrons in the highest (outermost) s and p orbitals of an atom

• The electrons available to be transferred or shared to create chemical bonds to form compounds

• Often found in incompletely filled energy levels

Valence ElectronsShortcut to finding valence electrons for main group elements

Family 1A (1) 1 valence electronFamily 2A (2) 2 valence electronsFamily 3A (13) 3 valence electronsFamily 4A (14) 4 valence electronsFamily 5A (15) 5 valence electronsFamily 6A (16) 6 valence electronsFamily 7A (17) 7 valence electronsFamily 8A (18) 8 valence electrons

Family 3-12 have multiple possibilities and shortcuts do not work

Electron Dot NotationElectron configuration notation using only the valence electrons of an

atom.

The valence electrons are indicated by dots placed around the element’s symbol.

Used to represent up to eight valence electrons for an atom. One dot is placed on each side before a second dot is placed on any side.

Valance Electrons: Sodium Magnesium Chlorine Neon

1 2 7 8

Electron Dot Notation: • • •• ••

Na Mg : Cl : : Ne : • • ••

Oxidation Numbers:+1 +2 -1 0

Unit 2 Part III Key Terms• Emission spectrum: The range of all possible wave frequencies of

electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields

• Energy Levels - A certain volume of space around the nucleus in which an electron is likely to be found. Energy levels start at level 1 and go to infinity.

• Excited state: The state of an atom when one of its electrons is in a higher energy orbital than the ground state.

• Gamma radiation: Electromagnetic radiation emitted during radioactive decay and having an extremely short wavelength

• Ground state: The lowest energy state of an atom or other particle• Planck’s constant: As frequency increases, the energy of the wave

increases

Electromagnetic (EM) Spectrum

• The EM Spectrum is the range of all possible wave frequencies of electromagnetic radiation, waves created by the systematic interactions of oscillating electric and magnetic fields

• The general term for all electromagnetic radiation is light• The range of the EM Spectrum is from very low frequency

known as radio waves to very high frequency known as gamma radiation

• The visible spectrum of light is in the center portion of this EM Spectrum

• All EM Spectrum travels at the same speed in a vacuum – this speed is known as the speed of light, 3.00 x 108 m/s

EM Spectrum

Image used courtesy of http://9-4fordham.wikispaces.com/Electro+Magnetic+Spectrum+and+light

Speed of Light and Frequency• Since the speed of all EM radiation is the same, there is a clear

mathematical relationship between the frequency of the light and its wavelength

• All waves travel at a speed that is equal to the product of its frequency (the reciprocal of time) and its wavelength (distance)

c = f λ• The speed of EM radiation is fixed at 3.00 x 108 m/s

• Therefore:3.00 x 108 m/s = f λ

Speed of light = frequency x wavelength• As frequency increases, wavelength decreases. As wavelength

increases, frequency decreases• Example: If frequency doubles, wavelength is cut in half

As f ↑, ↓λ : Calculations• If the wavelength of a radio wave is 15 meter, what is its

frequency?3.00 x 108 m/s = f (10 m)

(3.00 x 108 m/s) / 15 m = f2.0 x107 s-1 = f

Frequency = 2.0 x107 Hertz

• If the frequency of gamma radiation is 6.25 x 1022 Hertz, what is its wavelength?

3.00 x 108 m/s = (6.25 x 1022 s-1) λ(3.00 x 108 m/s) / (6.25 x 1022 s-1) = λ

4.80 x10-15 m = fWavelength = 4.80 x10-15 m

Planck’s Law• Max Planck determined in 1900 there was a mathematical

relationship between the energy of EM radiation and the frequency of that radiation:

As frequency increases, the energy of the wave increases

E = h f

Energy = Planck’s constant x frequencyE = (6.63 x 10-34 Joule seconds) f

Planck’s Law Calculations• Example: If the wavelength of green light is 5.21 x 10-7 meters,

what is the energy of this light?

3.00 x 108 m/s = f (5.21 x 10-7 m)(3.00 x 108 m/s) / 5.21 x 10-7 m = f

5.76 x1014 s-1 = fFrequency = 5.76 x1014 Hertz

E = (6.63 x 10-34 Joule seconds) (5.76 x1014 s-1)E = 3.82 x10-19 Joules

Implication of Planck’s Law• In order to move an electron to a higher energy level, excite an

electron, energy must be absorbed to move the electron• Since electrons exist in fixed energy levels with a specific

amount of energy, the amount of energy needed is a finite amount equal to the difference in the energy associated with the ground state of the electron and the energy associated with the level to which the electron is excited

• If the energy related to the excited electron is removed, the electron will return to its ground state and the energy released is equal to the energy absorbed to excite it

• The energy released is released as light• The overall result is that every element has a unique spectra of

light associated with it and the spectra can be used to identify the element