atomic structure ? kenneth e. schnobrich. a brief history about 460 b.c. - a greek philosopher,...
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ATOMIC STRUCTUREATOMIC STRUCTURE
?
Kenneth E. Schnobrich
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A Brief HistoryA Brief History
• About 460 B.C. - a Greek Philosopher, About 460 B.C. - a Greek Philosopher, Democritus, developed the idea of Democritus, developed the idea of atoms (atoms (atomos)atomos) as small indivisible as small indivisible particlesparticles
• About 400 B.C. - a number of Greek About 400 B.C. - a number of Greek philosophers said matter consisted of philosophers said matter consisted of FIRE, EARTH, WATER, and AIR.FIRE, EARTH, WATER, and AIR.
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A Brief HistoryA Brief History• NEXT 2000 YEARS - Alchemy (a pseudoscience) NEXT 2000 YEARS - Alchemy (a pseudoscience)
dominated - they were concerned with turning dominated - they were concerned with turning base metals into gold. During this time Hg, S, base metals into gold. During this time Hg, S, and Sb were discovered. Alchemists also and Sb were discovered. Alchemists also discovered how to make mineral acids.discovered how to make mineral acids.
• 1754-1826 Joseph Proust showed that a given 1754-1826 Joseph Proust showed that a given compound always had the same proportions by compound always had the same proportions by mass. mass. Law of Definite Proportions.Law of Definite Proportions.
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A Brief HistoryA Brief History• 1766-1844 - John Dalton (following the work of 1766-1844 - John Dalton (following the work of
Robert Boyle) discovered that atoms can Robert Boyle) discovered that atoms can combine in more than one way. He proposed combine in more than one way. He proposed the the Law of Multiple Proportions.Law of Multiple Proportions. He theorized He theorized that the basic unit was the that the basic unit was the atomatom. .
• 1808 - Michael Faraday worked on the 1808 - Michael Faraday worked on the electrolysis of molten salts and coined the word electrolysis of molten salts and coined the word ion (ion (Greek meaning wanderers).Greek meaning wanderers).
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A Brief HistoryA Brief History
• 1808 - John Dalton published “A New System 1808 - John Dalton published “A New System of Chemical Philosophy” which proposed his of Chemical Philosophy” which proposed his theory of atomstheory of atoms– All elements are composed of tiny, discrete, All elements are composed of tiny, discrete,
indivisible and indestructible particles called indivisible and indestructible particles called “atoms”.“atoms”.
– All atoms of a given element are identicalAll atoms of a given element are identical– Atoms of of different elements are different; they Atoms of of different elements are different; they
have different masses and properties.have different masses and properties.– Chemical combinations of these “atoms” compose all Chemical combinations of these “atoms” compose all
matter - different atoms combine differently to form matter - different atoms combine differently to form compounds.compounds.
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DALTON’S ATOMDALTON’S ATOM
JOHN DALTON - he envisioned the atom as a hard spherical unit of matter (the ultimate unit)
Lithium
Chlorine
Sulfur
LiCl
Li2S
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DALTON’S ATOMDALTON’S ATOM
JOHN DALTON - he envisioned the atom as a hard spherical unit of matter
Oxygen
Hydrogen
H2O
H2O2
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HISTORY (cont.)HISTORY (cont.)
• 1875 - Eugen Goldstein discovered the 1875 - Eugen Goldstein discovered the existence of a charged stream from the existence of a charged stream from the cathode using a “Crookes Tube” and called cathode using a “Crookes Tube” and called them “Cathode Rays”them “Cathode Rays”
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HISTORY (cont.)HISTORY (cont.)
• 1886 - Eugen Goldstein discovered the 1886 - Eugen Goldstein discovered the existence of positively charged particles he existence of positively charged particles he called “Canal Rays”called “Canal Rays”
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HISTORY (cont.)HISTORY (cont.)
• 1897 - J.J. Thomson using a modified “Crookes 1897 - J.J. Thomson using a modified “Crookes Tube” determined that the “Cathode Rays” Tube” determined that the “Cathode Rays” behaved like charged particles and measured behaved like charged particles and measured the charge.the charge.
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HISTORY (cont.)HISTORY (cont.)
• 1907 - J.J. Thomson proposed his 1907 - J.J. Thomson proposed his “Raisin Pudding Model” of the “Raisin Pudding Model” of the atom.atom.
--
--
---
- -
---
-
-
Negatively chargedElectrons
Positive Matrix
*Atoms are neutral
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HISTORY (cont.)HISTORY (cont.)
1911 - Ernest Rutherford suggested the 1911 - Ernest Rutherford suggested the atom was “nuclear” based on a famous atom was “nuclear” based on a famous experiment - “The Scattering experiment - “The Scattering Experiment”. He also suggested that Experiment”. He also suggested that the proton was the fundamental unit of the proton was the fundamental unit of positive chargepositive charge
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HISTORY (cont.)HISTORY (cont.)
AlphaParticles
Metal Foil(Au)
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ASSUMPTIONSASSUMPTIONSRUTHERFORD’S WORKRUTHERFORD’S WORK
• Most of the atoms mass is concentrated Most of the atoms mass is concentrated in the nucleus.in the nucleus.
• All of the positive charge is concentrated All of the positive charge is concentrated in the nucleusin the nucleus
• Neutral atoms have equal numbers of Neutral atoms have equal numbers of protons and electrons.protons and electrons.
• The protons and neutrons are located in The protons and neutrons are located in the nucleus of the atom.the nucleus of the atom.
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HISTORY (cont.)HISTORY (cont.)
THOMSON MODEL
RUTHERFORD MODEL
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HISTORY (cont.)HISTORY (cont.)
• 1932 - Chadwick discovered and 1932 - Chadwick discovered and determined the properties of the determined the properties of the neutron. neutron.
Proton
Neutron
NucleusElectrons
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SUBATOMIC PARTICLESSUBATOMIC PARTICLES
PARTICLEPARTICLE CHARGECHARGE MASSMASS LOCATIONLOCATION SYMBOLSYMBOL
PROTONPROTON +1+1 1 AMU1 AMU NUCLEUSNUCLEUS 11HH1 1 or or 11pp11
NEUTRONNEUTRON 00 1 AMU 1 AMU NUCLEUSNUCLEUS 00nn11
ELECTRONELECTRON -1-11/1836 1/1836 AMUAMU OUTSIDEOUTSIDE -1-1ee00
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LOOKING AT THE ATOMS LOOKING AT THE ATOMS STRUCTURESTRUCTURE
• Atomic NumberAtomic Number = # protons and = # protons and electrons in a neutral atomelectrons in a neutral atom
• Atomic Mass Number*Atomic Mass Number* = sum of the = sum of the protons and neutrons protons and neutrons
• #Neutrons#Neutrons = Mass# - Atomic# = Mass# - Atomic#
*ATOMIC MASS MAY VARY (ISOTOPES)
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ISOTOPESISOTOPESAVERAGE ATOMIC AVERAGE ATOMIC
MASSMASSMost of the elements on the periodic table have severalIsotopes. The Mass that you see is the weighted average of known isotopes.
Example: Carbon has two stable isotopesC12 = 98.89% and C13 = 1.108%
12(0.9889) + 13(0.01108) = 12.01
Average Atomic Mass
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FORMING AN IONFORMING AN ION
• METALS - usually like to lose METALS - usually like to lose electrons to form electrons to form positive ionspositive ions called called CATIONSCATIONS..
• NONMETALS - usually like to gain NONMETALS - usually like to gain electrons to form electrons to form negative ionsnegative ions called called ANIONSANIONS..
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FORMING IONSFORMING IONS
Na Na+1 + electron
Cl Cl-1+ electron
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Mn25
54.94
2-8-13-2
+2+3+4+7
Electron Arrangement
Atomic Number
Atomic Mass OxidationStates
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THE KERNELTHE KERNELANDAND
VALENCE ELECTRONSVALENCE ELECTRONS
19K39 2-8-8-1
Valence Electrons – those in the outer principal energylevel
Kernel – the nucleus and all of the electrons except those in the valence level
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THE KERNELTHE KERNELANDAND
VALENCE ELECTRONSVALENCE ELECTRONS
19K39 2-8-8-1
Valence Electrons = 1
Kernel – has a charge of +1
*Now Lewis Dot Structures
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LEWIS DOT STRUCTURES
19K39 2-8-8-1 K
16S-2 2-8-8 Sxx
[ ]-2
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PUTTING IT TOGETHERPUTTING IT TOGETHER
PARTICLEPARTICLE PROTONSPROTONS ELECTRONSELECTRONS NEUTRONSNEUTRONS
NN
NN-3-3
SnSn
ScSc+3+3
NaNa
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CONTINUOUSCONTINUOUSSPECTRUMSPECTRUM
VISIBLE REGION OF THE SPECTRUM
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HYDROGEN AND HELIUM HYDROGEN AND HELIUM LINE SPECTRUMLINE SPECTRUM
HYDROGEN
HELIUM
More spectra
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BRIGHT-LINE SPECTRABRIGHT-LINE SPECTRA
BRIGHT-LINE SPECTRA ARE LIKE FINGER PRINTS. EACH ELEMENT HAS ITS OWN CHARACTERISTIC SET OF BRIGHT LINES IN THE VISIBLE REGION OF THE SPECTRUM.
Carbon
Helium
Hydrogen
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THE BOHR MODELTHE BOHR MODEL
Bohr’s Model was based on the simplest atom, Hydrogen. Bohr based his model on the following:(1) Electrons do not follow the rules of large
macroscopic bodies.(2) Electrons in atoms have only specific energies.(3) Electrons are only in specific orbits outside the
nucleus (ground state).(4) When an electron moves from one orbit to
another it absorbs or releases energy of a specific frequency.
(5) When electrons absorb energy they move to an excited state (higher energy orbit).
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THE BOHR MODELTHE BOHR MODELHydrogenHydrogen
Excited State
Ground State
Energy ReleasedEnergy Absorbed
2
1
2
1
2
1
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THE QUANTUM MODELTHE QUANTUM MODEL
As the science of spectroscopy grew and the resolution of the bright-line spectra of an element improved and the dual nature of the electron was explored scientists formulated a new picture of the atom.
This new model of the atom retains some of the original features but changes the concept of electron location. The electron, instead of occupying a specific orbit now is thought to occupy a region of 3-D space called the orbital.
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THE QUANTUM MODELTHE QUANTUM MODEL
Dual Nature of the Electron – the electron to this point, had been described as being “particle-like” in nature, but it also exhibits “wave-like behavior.”DeBroglie – was the first to suggest that, based on its extremely small size, the electron does have a measureable wavelength.
Double-click on the You Tube video
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THE QUANTUM MODELTHE QUANTUM MODEL
After viewing the video we see that Erwin Schrodinger allows us to describe the electrons in an atom with a set of 4 Quantum Numbers.• The quantum numbers help us to describe the relative energies and probable locations of the electrons. •The Principal Quantum Number (n) – corresponds very closely with the energy levels described in the Bohr Model. The PQN can only have small whole number values (n = 1, 2, 3, 4, 5, 6 etc). The greater the value of “n” the greater the energy and distance from the nucleus for the electron.
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THE QUANTUM MODELTHE QUANTUM MODEL
• The Sublevel Quantum Number (l) – describes the sublevels the electrons can occupy within a Principal Energy Level. •The SQN – has values that are determined by the value of the PQN.• It can have values from 0 … n-1• So, if n = 0, l = 0• If n = 2, l = 0, 1 (which means, in the second Principal Energy Level, there are two available sublevels the electron can occupy.• There are also corresponding letter values for the sublevels 0(s); 1(p); 2(d); 3(f)
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THE QUANTUM MODELTHE QUANTUM MODEL
• In the 2nd PEL there were two sublevels, 0, 1 or s and p.• Within a PEL, as the value of l increases the energy and distance from the nucleus increases.• In the 3rd PEL, there are three sublevels, 0, 1, and 2 or s, p, and d sublevels.
•The Orbital Quantum Number (m) (also sometimes called the Magnetic Quantum number) - describes the number of orbitals (3-D orientations in space) within a sublevel.
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THE QUANTUM MODELTHE QUANTUM MODEL
• The OQN’s are determined by the values for l• m can have values from 0… +/- l• So, if l = 0, m = 0, which means that there is only one possible 3-D description (or orbital) in that sublevel.• If l = 1, m = 0, +1, -1, which means in the “p” sublevel there are three, 3-D descriptions (or orbitals), in that sublevel.
Along the X axis Along the Y axis Along the Z axis
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THE QUANTUM MODELTHE QUANTUM MODEL
• If an orbital is located in an s sublevel it is referred to as an s-orbital and has a spherical distribution along the X, Y, and Z axes.
• If an orbital is located in an p sublevel it is referred to as an p-orbital and has a “dumbell” distribution”along the X, Y, and Z axes.
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THE QUANTUM MODELTHE QUANTUM MODEL
• Of course there are other orbital shapes but they are complicated and for our purposes, our concerns will be limited to the s and p orbital shapes.• The fourth quantum number is the Spin Quantum Number – based on the Stern/Gerlach experiment it is thought that an electron can have one of two possible spins, +1/2 and -1/2 (it spins on its axis).• Since no two electrons can have exactly the same set of four quantum numbers, only two electrons can occupy an orbital, provided they have opposite spins.
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THE QUANTUM MODELTHE QUANTUM MODEL
• Based on the work of many scientists, including deBroglie, Shrodinger, and Heisenberg, we now know that –• we can only speak in terms of the probable location of the electrons• the bright line spectra available for the elements gives us additional information on the energy associated with the electrons
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THE QUANTUM MODEL THE QUANTUM MODEL OFOF
HYDROGENHYDROGEN
Note: the electron is pictured as a cloud or region of space where you will most probably find the electron.
Nucleus
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Quantum AtomQuantum AtomRelationshipsRelationships
1 orbital
s
3 orbitals
p
5-orbitals
d
7-orbitals
f
SUBLEVELS
ORBITPrincipal
Energy LevelIncreasing Energy
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Electron FillingElectron Filling
When we fill the energy sublevels that are several rules we must follow –• The Aufbau Principle – you must always fill from lowest energy to highest energy• Hund’s Rule – you must completely half-fill an energy sublevel before you start pairing electrons• Pauli Exclusion Principle – no two electrons can have the same set of four quantum numbers in a given orbital, they must have opposite spins to exist in the same orbital.
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Filling the Sublevels & OrbitalsFilling the Sublevels & Orbitals
• When filling the sublevels and orbitals remember the rules• It is also important to remember that for multi-electron atoms some of the sublevels do overlap from an energy standpoint.• there is a simplified relationship to help us with this overlap – Sublevel Energy = n + l (n is the PQN and l is the SQN ). It is why the 4s sublevel fills before the 3d sublevel (see the diagram on the next slide).• 4s = 4 + 0 = 4 and 3d = 3 + 2 = 5• the sublevel energy of 4s is lower than that of 3d, therefore, the 4s sublevel fills before the 3d sublevel.
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General SublevelGeneral SublevelArrangementArrangement
En
ergy
Dis
tan
ce f
rom
Nu
cleu
s
1s
2s
2p
3s
3p
4s
3d
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General SublevelGeneral SublevelArrangementArrangement
1s2s 2p
3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f
* The idea of sublevel overlap can be much more complicated for larger atoms
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General SublevelGeneral SublevelArrangementArrangement
En
ergy
Dis
tan
ce f
rom
Nu
cleu
s
1s
2s
2p
3s
3p
4s
3d
For 19K39 the sublevel filling would look like this
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General SublevelGeneral SublevelArrangementArrangement
En
ergy
Dis
tan
ce f
rom
Nu
cleu
s
1s
2s
2p
3s
3p
4s
3d
For 7N14 the sublevel filling would look like this
Note: the sublevel is half-filled, the electrons have parallel spins (the same)
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Electron ArrangementElectron Arrangement
Let’s take a sample and show you how the electron arrangement can be written in three formats.
19K39 2-8-8-1
19K39 1s22s22p63s23p64s1
19K39 [Ar]4s1
4s1 # of electronsEnergy sublevel
Principal EnergyLevel