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ElectronicStructureof Atoms
Electronic Structure of Atoms
Resources• Our TB: Ch. 6 of Chemistry: The Central
Science AP version (10th edition)
• Powerpoint * (from pearson) and in-class work
• POGIL activities: (1) Analysis of Spectral Lines and (2) Interaction of Radiation and Matter
• Online resources for our TB (in particular online quiz)
• Chem tours from ch. 7 of the W.W. Norton online book by Gilbert:
• http://www.wwnorton.com/college/chemistry/gilbert2/contents/ch07/studyplan.asp
• Animations from Glencoe site:http://glencoe.mcgraw-hill.com/sites/0023654666/student_view0/chapter7/
• Extra quizzes from Glencoehttp://glencoe.mcgraw-hill.com/sites/0023654666/student_view0/chapter7/
• Video lectures from chem guy http://www.kentchemistry.com/moviesfiles/chemguy/AP/ChemguyAtomicTheory.htm
• Handouts and practice problems from M. Brophy’s web site
ElectronicStructureof Atoms
Chapter 6Electronic Structure
of Atoms
Chemistry, The Central Science, 10th editionTheodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
John D. BookstaverSt. Charles Community College
St. Peters, MO 2006, Prentice Hall, Inc.
ElectronicStructureof Atoms
Waves
• To understand the electronic structure of atoms, one must understand the nature of electromagnetic radiation.
• The distance between corresponding points on adjacent waves is the wavelength ().
ElectronicStructureof Atoms
Waves• The number of waves
passing a given point per unit of time is the frequency ().
• For waves traveling at the same velocity, the longer the wavelength, the smaller the frequency.
ElectronicStructureof Atoms
Electromagnetic Radiation
• All electromagnetic radiation travels at the same velocity: the speed of light (c), 3.00 108 m/s.
• Therefore,
c =
ElectronicStructureof Atoms
The Nature of Energy• The wave nature of light
does not explain how an object can glow when its temperature increases.
• Max Planck explained it by assuming that energy comes in packets called quanta.
ElectronicStructureof Atoms
The Nature of Energy
• Einstein used this assumption to explain the photoelectric effect.
• He concluded that energy is proportional to frequency:
E = hwhere h is Planck’s constant, 6.63 10−34 J-s (i.e. units for h are J•s)
ElectronicStructureof Atoms
The Nature of Energy
• Therefore, if one knows the wavelength of light, one can calculate the energy in one photon, or packet, of that light:
c = E = h
ElectronicStructureof Atoms
For electromagnetic radiation animation and problems see:
http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_07&folder=frequency_wavelength
For All Chem tours for the electrons in atoms and periodic properties topic see:
http://www.wwnorton.com/college/chemistry/gilbert2/contents/ch07/studyplan.asp
Recommeded chem tours animations:
Electromagnetic radiation
Light Emission and Absorbtion
Bohr Model of the Atom
De Broglie Wavelngth
Quantum numbers
Electron configuration
ElectronicStructureof Atoms
The Nature of Energy
Another mystery involved the emission spectra observed from energy emitted by atoms and molecules.
ElectronicStructureof Atoms
The Nature of Energy
• One does not observe a continuous spectrum, as one gets from a white light source.
• Only a line spectrum of discrete wavelengths is observed.
ElectronicStructureof Atoms
Go To Glencoe Animationhttp://glencoe.com/sites/common_assets/advanced_placement/chemistry_chang9e/animations/chang_7e_esp/pem1s3_1.swf
POGIL activity on Spectral Lines
(To Complete)
ElectronicStructureof Atoms
The Nature of Energy
• Niels Bohr adopted Planck’s assumption and explained these phenomena in this way:1. Electrons in an atom can only
occupy certain orbits (corresponding to certain energies).
ElectronicStructureof Atoms
The Nature of Energy
• Niels Bohr adopted Planck’s assumption and explained these phenomena in this way:2. Electrons in permitted orbits
have specific, “allowed” energies; these energies will not be radiated from the atom.
ElectronicStructureof Atoms
The Nature of Energy
• Niels Bohr adopted Planck’s assumption and explained these phenomena in this way:3. Energy is only absorbed or
emitted in such a way as to move an electron from one “allowed” energy state to another; the energy is defined by
E = h
ElectronicStructureof Atoms
The Nature of EnergyThe energy absorbed or emitted from the process of electron promotion or demotion can be calculated by the equation:
E = −RH ( )1nf
2
1ni
2-
where RH is the Rydberg constant, 2.18 10−18 J, and ni and nf are the initial and final energy levels of the electron.
ElectronicStructureof Atoms
Go To Glencoe and Norton Animationshttp://glencoe.com/sites/common_assets/advanced_placement/chemistry_chang9e/animations/chang_7e_esp/pem1s3_1.swf
POGIL activity on Interaction of Radiation and Matter
(To Complete)
Go to Chem tour for Bohr Model of atom (and Rydberg equation)
http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_07&folder=hydrogen_energies
ElectronicStructureof Atoms
The Wave Nature of Matter
• Louis de Broglie posited that if light can have material properties, matter should exhibit wave properties.
• He demonstrated that the relationship between mass and wavelength was
=h
mv
ElectronicStructureof Atoms
The Uncertainty Principle
• Heisenberg showed that the more precisely the momentum of a particle is known, the less precisely is its position known:
• In many cases, our uncertainty of the whereabouts of an electron is greater than the size of the atom itself!
(x) (mv) h4
ElectronicStructureof Atoms
Quantum Mechanics
• Erwin Schrödinger developed a mathematical treatment into which both the wave and particle nature of matter could be incorporated.
• It is known as quantum mechanics.
ElectronicStructureof Atoms
The Quantum Mechanical Model
• Energy is quantized - It comes in chunks.
• A quantum is the amount of energy needed to move from one energy level to another.
• Since the energy of an atom is never “in between” there must be a quantum leap in energy.
• In 1926, Erwin Schrodinger derived an equation that described the energy and position of the electrons in an atom
• (this slide from: J. Hushen’s presentation on Atomic Structure at http://teachers.greenville.k12.sc.us/sites/jhushen/Pages/AP%20Chemistry.aspx)
ElectronicStructureof Atoms
Schrodinger’s Wave Equation22
2 2
8dh EV
m dx
Equation for the probabilityprobability of a single electron being found along a single axis (x-axis)Erwin Schrodinger
(this slide from: J. Hushen’s presentation on Atomic Structure at http://teachers.greenville.k12.sc.us/sites/jhushen/Pages/AP%20Chemistry.aspx)
ElectronicStructureof Atoms
Quantum Mechanics
• The wave equation is designated with a lower case Greek psi ().
• The square of the wave equation, 2, gives a probability density map of where an electron has a certain statistical likelihood of being at any given instant in time.
ElectronicStructureof Atoms
Quantum Numbers
• Solving the wave equation gives a set of wave functions, or orbitals, and their corresponding energies.
• Each orbital describes a spatial distribution of electron density.
• An orbital is described by a set of three quantum numbers.
ElectronicStructureof Atoms
Principal Quantum Number, n
• The principal quantum number, n, describes the energy level on which the orbital resides.
• The values of n are integers ≥ 0.
ElectronicStructureof Atoms
Azimuthal Quantum Number, l
• This quantum number defines the shape of the orbital.
• Allowed values of l are integers ranging from 0 to n − 1.
• We use letter designations to communicate the different values of l and, therefore, the shapes and types of orbitals.
ElectronicStructureof Atoms
Azimuthal Quantum Number, l
Value of l 0 1 2 3
Type of orbital s p d f
ElectronicStructureof Atoms
Magnetic Quantum Number, ml
• Describes the three-dimensional orientation of the orbital.
• Values are integers ranging from -l to l:
−l ≤ ml ≤ l.
• Therefore, on any given energy level, there can be up to 1 s orbital, 3 p orbitals, 5 d orbitals, 7 f orbitals, etc.
ElectronicStructureof Atoms
Magnetic Quantum Number, ml
• Orbitals with the same value of n form a shell.• Different orbital types within a shell are
subshells.
ElectronicStructureof Atoms
Level n 1 2 3
Sublevel l Orbital ml
Spin ms
0 0
0 0 1 0 -1 0 1 0 -1 2 1 0 -1 -2
2101
= +1/2
= -1/2
Allowed Sets of Quantum Numbers for Electrons in Atoms
ElectronicStructureof Atoms
s Orbitals
• Value of l = 0.• Spherical in shape.• Radius of sphere
increases with increasing value of n.
ElectronicStructureof Atoms
s Orbitals
Observing a graph of probabilities of finding an electron versus distance from the nucleus, we see that s orbitals possess n−1 nodes, or regions where there is 0 probability of finding an electron.
ElectronicStructureof Atoms
p Orbitals
• Value of l = 1.• Have two lobes with a node between them.
ElectronicStructureof Atoms
d Orbitals• Value of l is 2.• Four of the
five orbitals have 4 lobes; the other resembles a p orbital with a doughnut around the center.
ElectronicStructureof Atoms
Energies of Orbitals
• For a one-electron hydrogen atom, orbitals on the same energy level have the same energy.
• That is, they are degenerate.
ElectronicStructureof Atoms
Energies of Orbitals
• As the number of electrons increases, though, so does the repulsion between them.
• Therefore, in many-electron atoms, orbitals on the same energy level are no longer degenerate.
ElectronicStructureof Atoms
Spin Quantum Number, ms
• In the 1920s, it was discovered that two electrons in the same orbital do not have exactly the same energy.
• The “spin” of an electron describes its magnetic field, which affects its energy.
ElectronicStructureof Atoms
Spin Quantum Number, ms
• This led to a fourth quantum number, the spin quantum number, ms.
• The spin quantum number has only 2 allowed values: +1/2 and −1/2.
ElectronicStructureof Atoms
Pauli Exclusion Principle
• No two electrons in the same atom can have exactly the same energy.
• For example, no two electrons in the same atom can have identical sets of quantum numbers.
ElectronicStructureof Atoms
Go To www.ptable.com IMPORTANT
Use periodic Table to help you write electron configurations of atoms (and ions)
Dynamic Periodic Table and Investigate (play with) the Orbitals option (on Top Tabs) for quantum numbers, orbitals and electron configurations of various elements
Go To
Glencoe site for animations on electron configuration
http://glencoe.mcgraw-hill.com/sites/0023654666/student_view0/chapter7/animations_center.html#
ElectronicStructureof Atoms
Electron Configurations
• Distribution of all electrons in an atom
• Consist of Number denoting the
energy level
ElectronicStructureof Atoms
Electron Configurations
• Distribution of all electrons in an atom
• Consist of Number denoting the
energy level Letter denoting the type
of orbital
ElectronicStructureof Atoms
Electron Configurations
• Distribution of all electrons in an atom.
• Consist of Number denoting the
energy level. Letter denoting the type
of orbital. Superscript denoting the
number of electrons in those orbitals.
ElectronicStructureof Atoms
Orbital Diagrams
• Each box represents one orbital.
• Half-arrows represent the electrons.
• The direction of the arrow represents the spin of the electron.
ElectronicStructureof Atoms
Hund’s Rule
“For degenerate orbitals, the lowest energy is attained when the number of electrons with the same spin is maximized.”
ElectronicStructureof Atoms
Periodic Table
• We fill orbitals in increasing order of energy.
• Different blocks on the periodic table, then correspond to different types of orbitals.
ElectronicStructureof Atoms
Some Anomalies
Some irregularities occur when there are enough electrons to half-fill s and d orbitals on a given row.
ElectronicStructureof Atoms
Some Anomalies
For instance, the electron configuration for copper is
[Ar] 4s1 3d5
rather than the expected
[Ar] 4s2 3d4.
ElectronicStructureof Atoms
Some Anomalies
• This occurs because the 4s and 3d orbitals are very close in energy.
• These anomalies occur in f-block atoms, as well.
ElectronicStructureof Atoms
ELECTRON SPIN•1920--chemists realized that since electrons interact with a magnetic field, there must be one more concept to explain the behavior of electrons in atoms.•ms--the 4th quantum number; accounts for the reaction
of electrons in a magnetic field MAGNETISM•magnetite--Fe3O4, natural magnetic oxide of iron•1600--William Gilbert concluded the earth is also a large spherical magnet with magnetic south at the north pole (Santa's habitat).•NEVER FORGET: opposites attract & likes repel
PARAMAGNETISM AND UNPAIRED ELECTRONS•diamagnetic--not magnetic [magnetism dies]; in fact they are slightly repelled. All electrons are PAIRED.•paramagnetic--attracted to a magnetic field; lose their magnetism when removed from the magnetic field; HAS ONE OR MORE UNPAIRED ELECTRONS•ferromagnetic--retain magnetism upon introduction to, then removal from a magnetic field•All of these are explained by electron spins•Each electron has a magnetic field with N & S poles•electron spin is quantized such that, in an external magnetic field, only two orientations of the electron magnet and its spin are possible•+/- 1/2•H is paramagnetic; He is diamagnetic, WHY?•H has one unpaired electron•He has NO unpaired electrons; all spins offset and cancel each other out
•(Taken from summary notes posted on M. Brophy’s website)
ElectronicStructureof Atoms
•What about ferromagnetic?clusters of atoms have their unpaired electrons aligned within a cluster, clusters are more or less aligned and substance acts as a magnet. Don't drop it!!
•When all of the domains, represented by these arrows are aligned, it behaves as a magnet. This is what happens if you drop it! The domains go indifferent directions and it no longer operates as a magnet.
(Taken from summary notes posted on M. Brophy’s website)
ElectronicStructureof Atoms
Activities and Problem set __
TB ch. 6 – all sections required for SAT II and AP exams and most are required for regents exam
View and take notes on the recommended animations
POGIL activities on (1) Analysis of Spectral Lines and (2) Interaction of Radiation and Matter
Online practice quiz due by ______
• Ch 6 Problems: write out questions (or
photocopy them) ; write out answers &
show work
• First carefully study the sample
exercises in chapter 6 (you don’t have to
copy them out) and then DO all in-
chapter practice exercises according to
the directions above.
• Do all GIST, and Visualizing concepts,
problems
• end of chapter 6 exercises: _________