Unit II
Atomic History, Theory & Structure
Textbook Chapters 3 and 4
Image taken from http://www.universetoday.com/wp-content/uploads/2010/02/c-atom_e1.gif on 8/8/11.
How small is small?
• Greeks “Atomos”
• Democritus 430 B.C.
•
Continuous vs. Discontinuous Theory of Matter
Earliest Models (9min video)
Image taken from http://www.universetoday.com/wp-content/uploads/2009/12/Democritus.jpg on 8/8/11
.
3 Laws that Support Existence of
Atoms
1. The Law of Definite Proportions
2. The Law of Conservation of Mass
3. The Law of Multiple Proportions
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Image taken from http://wikis.lawrence.edu/display/CHEM/1++Laura+Qiu on 8/8/11.
John Dalton’s Atomic Theory
Smaller than small
(1808)
video(9min video)
1. All matter is composed
of extremely small
particles called atoms,
which cannot be
subdivided, created or
destroyed.
Image taken from http://www.elmhurst.edu/~chm/vchembook/101Aatoms.html on 8/8/11.
Dalton’s Atomic Theory Continued
2. Atoms of a given element are identical in
their physical and chemical properties.
Dalton’s Atomic Theory Continued
3. Atoms of
different
elements differ
in their physical
and chemical
properties.
Image taken from http://www.wired.com/images/article/full/2008/09/Dalton_atomic_symbols.jpg on 8/8/11.
Dalton’s Atomic Theory Continued
4. Atoms of different elements combine in
simple, whole-number ratios to form
compounds.
Image taken
from
http://www.p
hysicalgeogr
aphy.net/fun
damentals/i
mages/com
pounds_mol
ecules.jpg
on 8/8/11.
Dalton’s Atomic Theory Continued
5. In chemical reactions, atoms are
combined, separated or rearranged but
never created, destroyed or changed.
Image taken from http://www.personal.kent.edu/~cearley/ChemWrld/balance/H2_O2.gif on 8/8/11.
My Gosh! Atoms are Divisible.
• J.J. Thomson (1897)
– Discovers electrons with cathode ray tube experiment.
– “Plum pudding” or “Chocolate chip cookie” atomic model
1906 Nobel Prize winner
CRT Video
Image taken from
http://nobelprize.org/nobel_prizes/physics/laureates/1906/th
omson.jpg on 8/8/11.
Positive
atom with
negative
charges
embedded
throughout
Image taken from http://www.kentchemistry.com/links/AtomicStructure/plum.gif on 8/8/11.
Millikan’s Oil Drop Experiment
• American Robert
Millikan, 1909.
• Determined the
mass of an e-.
• e- mass found to be
9.11 X 10-28g
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Image taken from http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan.jpg on 8/8/11.
Bye Plum Pudding, Hello Solar System Model
• Ernest Rutherford (1911)
–
–
–
Former student of Thomson.
Designed “gold foil” experiment
Conclusions
1. Most of atom is empty space.
2. Mass of atom is concentrated in very,
very small dense center (nucleus).
3. Nucleus has a positive charge.
1908 Nobel Prize
winner
Image taken from
http://nobelprize.org/nobel_prizes/chemistry/laureates/
1908/rutherford.jpg on 8/8/11.
Gold Foil animation
Relative size animation
Image taken from
http://web.neo.edu/rjones/Pages/1014new/Lecture/chemistry/chapter_8/images/
rutherford_model.jpg on 8/8/11.
Image taken from http://www.rsc.org/chemsoc/timeline/graphic/1911_gfoil_02.jpg on 8/8/11.
Subatomic Particles (Ref Table O)
Name
Symbol Mass
Charge Location
Proton
1 amu
+1
nucleus
Neutron
1amu
0
nucleus
(neutral)
Electron
Zero
(1/1836 amu)
-1
Outside
nucleus in
electron
cloud
• An atomic mass unit (amu)= 1/12 the mass of 12C atom
What subatomic particles have mass?
• Nucleons-subatomic particles (protons & neutrons)
containing mass found in nucleus
• Atomic Number (Z)-equal to # of protons in nucleus
of an atom.
• Mass Number (A)-equal to # of nucleons in an atom.
# of neutrons= A-Z
Neutron Discovered
(1932) by James
Chadwick. Won
1935 Nobel Prize.
Image taken from
http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick.jpg on 8/8/11.
Image taken from
http://www.windows2universe.org/physical_science/physics/atom_particle/atomic_mass_numb
er_sm.gifon 8/8/11.
Englishman Henry Moseley first
determined atomic numbers of
the elements by using x-rays.
Isotopes
• Atoms with the
same atomic # but
different # of
neutrons
• Affects mass.
• For a given
element, # of
protons is always
constant, # of
neutrons may vary.
Image taken from http://earthguide.ucsd.edu/virtualmuseum/images/raw/LO_Fig6_1_2.jpg on 8/8/11.
Atomic Mass
• Different than Mass Number
• The weighted average mass of the
naturally occurring isotopes of an element.
• Listed on Periodic Table (PT)
Try an example:
Neon-20 90.92%
Neon-21 0.257%
Neon-22 8.82%
Image taken from http://sulfur.nigc.ir/sulfurfacts-isotopes-en.html on 8/8/11.
Duality of Atomic Mass
12.0111
C
• Use Atomic Mass from PT.
6
2-4
• Remember Atomic Mass can be
measured in either amu’s or grams.
• If grams, then gram atomic mass (mass of
one mole of atoms of that element).
• If amu’s, then weighted avg.atomic mass
(mass of one atom of that element).
• Example:
Image taken from http://www.the-engagement-ring-guide.com/images/what-is-a-diamond.jpg on 8/8/11.
Mass Spectrometer
• Instrument that separates isotopes of an
element based on differences in their
mass.
Image taken from http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch13/figures/1334.gif on 8/8/11.
Electrons
• If atom is neutral, e- =
»
p+
Super Cation
• If not, have an ion.
• Ion- a charged atom.
• Lose electron(s) form
positive ion (cation).
• Gain electron(s) form
negative ion (anion).
• Which ions do metals
form? Nonmetals?
Concept Map Review
Image taken from http://usd388.k12.ks.us/highschool/faculty/david_wildeman/Ch.%203%20-%20Earth%20Science.htm on 8/8/11.
First Ionization Energy
• Amount of energy needed to remove the most
loosely bound electron from an atom.
• Reference Table S
• Removal of additional e- from an ion becomes
more difficult due to imbalance between positive
nuclear charge and remaining electrons.
•What happens to
ionization energy as you
go down a group on the
PT? Why?
•How about when you go
left to right across a
period on the PT? Why?
•Metals? Nonmetals?
Image taken from http://websites.pdesas.org/jvogus/2010/5/18/44324/page.aspx on 8/8/11.
• Metals
Ionic Radius
• Small # of valence e• Lose e- to form ion
• Ionic radius is smaller
than atomic radius.
• Nonmetals
• Large # of valence e• Gain e- to form ion
• Ionic radius is larger
than atomic radius.
Image taken from http://www.uwec.edu/boulteje/Boulter103Notes/23October.htm on 8/8/11.
Bohr Model of Atom
• Neils Bohr (1913)
– Electrons orbit nucleus
in distinct energy
levels or electron
shells (1-7 or K-Q).
– Energy levels are not
flat paths but instead
approximations of
electron position.
1922 Nobel
Prize Winner
Image taken from
http://nobelprize.org/nobel_prizes/physics/laure
ates/1922/bohr.jpg on 8/8/11.
Hydrogen atom animation
Image taken from http://images.tutorvista.com/content/atom/neils-bohr-model-atom.gifon 8/9/11.
I’m so Excited this is not Bohring!!!
• Ground StateElectrons are in
lowest available
energy level.
• Excited StateElectrons absorb
energy and shift to
higher energy
level.
• Become unstable,
so……
• Fall back to ground
state and release
energy that is a
difference between
the 2 energy levels
(Quanta)
Image taken from http://library.thinkquest.org/19662/images/eng/pages/model-bohr-2.jpg on 8/9/11.
Quantum Leap
• Quantum (plural Quanta):
– Discrete amount of energy that is absorbed or
released by electron.
– Quanta are also called photons.
Animation
Image taken from
http://library.thinkquest.org/C006669/media/Che
m/img/bohr.gif on 8/9/11.
• Lyman series
• emits photons of UV.
• e- drops to n=1.
• Balmer series
• emits photons of visible light.
• e- drops to n=2.
• Paschen series
• emits photons of infrared.
• e- drops to n=3.
Image taken from
http://outreach.atnf.csiro.au/education/senior/astr
ophysics/images/spectra/bohrhydrogen.gif on
8/9/11.
Electromagnetic Spectrum
Balmer Series illustration
Spectral Lines
• Electrons in excited state return to ground state.
• Emit energy.
• Quanta of radiant energy emitted has a
characteristic wavelength and frequency. We
can measure the wavelength or observe as a
different color.
• Applications:
• Fluorescent lights, fireworks, neon lights, flame tests
Image taken from http://www.astronomyknowhow.com/pics-res/hydrogen-spectra.jpg on 8/9/11.
Types of Spectra
• Bright line (explained)
• Absorption
• Spectroscopeinstrument used to
observe spectra.
Image taken from
http://www.scitechantiques.com/spectroscope_move/SourceSpectroscopeV3.jpg on
8/9/11.
Image taken from
http://teachers.bcps.org/teachers_sec/jsmith10/images/F8CE172A0F6B441C833A9A0E5E
9D7830.jpg on 8/9/11.
Problems with Bohr’s Model
• Worked well for H but not larger atoms.
• e- follow quantum or wave mechanics, not
classic mechanics.
• Max Planck(1900)light acts like both a particle
and also a wave, EM energy is quantized.
• Louis de Broglie(1927) e- can act like waves.
• Werner Heisenberg(1927)Uncertainty principle
(can’t be certain of both location & velocity of e-)
• Heisenberg and Erwin Schrodingere- is bound
to nucleus in manner similar to standing wave.
Image taken from http://www.scienceclarified.com/images/uesc_02_img0063.jpg on 8/8/11.
If I have seen
further, it is only
by standing on
the shoulders of
giants.
Image taken from
http://www.notablebiographies.com/images/uewb_07_img0519.jpg on 8/8/11.
-Issac Newton 1676
Alignment of Platinum atoms
within a crystal.
Image was taken with a Scanning Tunneling Microscope
from http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Graphics/IBMPlatinum.jpe on 8/2/11.
Modern Model
(Atomic Orbital/Electron Cloud/Wave-Mechanical)
• Can not be precise
about e- location.
• Electrons occupy
orbitals.
• Orbitalsaverage
region of the most
probable e- location.
• Orbitals differ in
shape, size and
orientation in space.
Electron Cloud Animation
Image taken from http://www.webelements.com/nexus/sites/default/files/images/orbitron-d.jpgon 8/9/11.
Modern Quantum Model
• To define the region
where electrons are
found, scientists
assign 4 Quantum
numbers (n,ℓ,mℓ,ms).
• To explain the 4
Quantum numbers, I
will use a Hotel
Analogy (H.A.).
Placing electrons
within the e- cloud is
like placing people in
a hotel.
The Principal Quantum Number (n)
• Principal energy level or shell
• Same as the period # on the P.T. for an element.
• H.A.- similar to the hotel floor.
Maximum # of e- per energy level = 2n2
Image taken from http://wiki.openeducationproject.info/images/1/1c/Orbitals.jpg on 8/9/11.
The
nd
2
Quantum Number (ℓ)
Angular Momentum Quantum Number (ℓ)
• Sublevels
• s, p, d, f
• (lowesthighest
energy)
• # of sublevels for
each principal energy
level = # of that
principal energy level
• H.A.-Wings of rooms
on a floor.
ℓ
n
1
1s
2
2s, 2p
3
3s,3p,3d
4**
4s,4p,4d,4f
** n can be higher than 4 but the sublevels do not get higher than f
The 3rd Quantum Number (mℓ)
Magnetic Quantum Number (mℓ)
• Orbitals (H.A. the rooms)
• Each sublevel may consist of one or more
orbitals with each orbital having a different
spatial orientation.
• Orbitals contain electrons. Use a box to
notate.
• No more than 2 e- in an orbital.
•
•
•
•
s sublevel  1 orbital
p sublevel  3 orbitals
d sublevel  5 orbitals
f sublevel  7 orbitals
Image taken from http://www.emc.maricopa.edu/faculty/farabee/biobk/orbitals.gif on 8/9/11.
th
4
Quantum number (ms)
Spin Quantum number (ms)
• Spin of the electron
• In order for 2 electrons to occupy the
same orbital, must have opposite spins.
• To notate, use arrows in the box (orbital).
• H.A.-One bed can fit 2 people, must sleep
opposite, head to toe, toe to head.
Orbitals animation in Real Player Library
Image taken from
http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/graphics/C3_quant_04.
gif on 8/9/11.
Electron Configuration Rules
1. No more than 2 e- can be in an orbital.
(Pauli exclusion principle, 1925).
2. Added e- is placed in unfilled orbital of
lowest energy.(The Aufbau principle).
3. 2 e- in an orbital have opposite spins.
4. In a given sublevel, a 2nd e- is not added
to an orbital until each orbital in the
sublevel contains one e- (Hund’s Rule of
Maximum Multiplicity).
Image taken from http://wps.prenhall.com/wps/media/objects/1054/1079855/IMAGES/AAALUMY0.jpg on 8/9/11.
Electron Configuration and
Notation Examples
• Superscript following each sublevel = # of
e- in that sublevel.
• Try examples:
– Cl
– Zr
Image taken from
http://wps.prenhall.com/wps/media/objects/1054/1079855/IMAGES/AAALUMY
0.jpg on 8/9/11.
Image taken from http://chemfionaflora.blogspot.com/2011_05_01_archive.html on 8/9/11.
How to remember the sublevel
overlap at higher energy levels?
• Diagonal Rule for
Electron
Configuration
– Number 1-7
vertically on paper in
4 columns.
– Write s2, p6, d10,f14
after the #’s.
– Draw in first 2
arrows then add rest
diagonally.
Image taken from
http://abacus.bates.edu/acad/depts/biobook/spdf.bmp on 8/9/11.
Valence Electrons
• e-’s in the outermost principal energy level
of an atom (“The Penthouse Electrons”)
• Look at Group #, (1,2,13-18) PT
• Important in chemical properties, behavior
and bonding.
Image taken from http://hyperphysics.phy-astr.gsu.edu/hbase/solids/imgsol/valen.gifon 8/9/11.
Valence Electrons & Stability
• We will learn in the next unit
that atoms bond to become
stable.
• Stability is achieved when
the s and p orbitals are
complete (8 valence e-).
• Noble gases already have a
stable octet (8 valence e-)
and therefore do not readily
bond. Exception is Helium
w/ 2 in valence.
Image taken from http://www.chemistryland.com/CHM130W/11Bonds/Octet.jpg on 8/9/11.
Kernel
• All parts of an atom except valence e• Nucleus and inner e-
Lewis Electron Dot Diagrams
•Kernel=Symbol
•Valence electrons=dots
Image taken from http://academic.brooklyn.cuny.edu/biology/bio4fv/page/oxygen-atom.JPG on 8/9/11.
Atomic Radius
• Half the distance between adjacent atoms
or
• Distance from the nucleus to the valence e-
Image taken from http://www.tutorvista.com/content/science/science-ii/periodic-classification-elements/trends.phpon 8/9/11.
Atomic Radius continued
• Ref Table S
• What happens to the
atomic radius as you go
down a group on the
PT? Why?
• How about left to right
within a period of the
PT? Why?
Both images taken from
http://www.tutorvista.com/content/science/science-ii/periodicclassification-elements/trends.php on 8/9/11.