electrons. the modern atom not along after rutherford established that the positive charge in the...
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ElectronsElectrons
The Modern AtomThe Modern AtomNot along after Rutherford established that the positive charge in the atom resided in the nucleus. Scientists began putting together a new model of the atom using other discoveries that had previously not been explainable.
The main discovery that got them rethinking the atom was the realization that the energy of light is quantized.
Bohr’s ModelBohr’s Model
developed the developed the planetary model of the planetary model of the atomatom
the paths the the paths the electrons “traveled” electrons “traveled” were referred as were referred as orbitalsorbitals
energies were energies were determined by the determined by the order from the nucleusorder from the nucleus
Bohr’s ModelBohr’s Model
When energy is added to When energy is added to an atom it causes an atom it causes electrons to move from an electrons to move from an orbital close to the orbital close to the nucleus to orbitals that nucleus to orbitals that are farther away. are farther away.
Starting Orbital = Ground Starting Orbital = Ground StateState
Higher Energy = Excited Higher Energy = Excited StateState
Quantum: Quantum: •of energy is the amount of energy of energy is the amount of energy required to move an electron from one required to move an electron from one energy level to another. energy level to another. • the energy of the electron is quantized the energy of the electron is quantized • a quantum leap is an abrupt changea quantum leap is an abrupt change
The quantum of electromagnetic radiation is the photon.
Light is EnergyLight is Energy
Neils BohrNeils Bohr
Studied the Studied the Hydrogen line Hydrogen line spectrumspectrum
Energy is closely Energy is closely related to its colorrelated to its color
What is Light?What is Light?
•Light is how we refer to Light is how we refer to Electromagnetic RadiationElectromagnetic Radiation•Electromagnetic Radiation applies Electromagnetic Radiation applies to infrared light, UV light, to infrared light, UV light, microwaves, radio waves, X-Rays etc.microwaves, radio waves, X-Rays etc.•Light is a waveLight is a wave
Bozeman WavesBozeman Waves
speed
WavesWaves
• An Analogy: An Analogy: • The waves of the ocean can The waves of the ocean can
transmit huge amounts of transmit huge amounts of energy, even though they energy, even though they aren’t concrete objects.aren’t concrete objects.
Wavelength and Wavelength and FrequencyFrequency
λλ = wavelength = wavelengthνν = frequency = frequencyc = speed of c = speed of lightlight(3.00 e(3.00 e88 m/s) m/s)
c = c = λ νλ ν
Bozeman LightBozeman Light
Spectrum of White Spectrum of White LightLight
ElecElectrotromagmagneticnetic SpeSpectctrumrumElecElectrotromagmagneticnetic SpeSpectctrumrum
In increasing energy,In increasing energy, RROOYY GG BBIIVV
An excited lithium atom An excited lithium atom emitting a photon of red emitting a photon of red light to drop to a lower light to drop to a lower energy state.energy state.
Flame TestFlame Test
Energy of Light is Related to Energy of Light is Related to FrequencyFrequency
E = hE = hνν•E = energy in JoulesE = energy in Joules•h = Plank’s constant = 6.626 eh = Plank’s constant = 6.626 e-34 -34 JsJs•νν = frequency (in Hz or /sec) = frequency (in Hz or /sec)
Ex: Light with a frequency of Ex: Light with a frequency of 450 GHz has an energy of 3.0 e450 GHz has an energy of 3.0 e--
2222 J J
Diffraction of ElectronsDiffraction of Electrons
Electrons as WavesElectrons as WavesLouis de BroglieLouis de Broglie (1924) (1924)
Applied wave-particle theory to eApplied wave-particle theory to e--
ee-- exhibit wave properties exhibit wave properties
QUANTIZED WAVELENGTHS
Electrons as WavesElectrons as Waves
EVIDENCE: DIFFRACTION PATTERNS
ELECTRONSVISIBLE LIGHT
Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple
• It is impossible It is impossible to know exactly to know exactly both the both the velocity (speed velocity (speed and direction) and direction) and position of a and position of a particle at the particle at the same time.same time.
Erwin Schrodinger Erwin Schrodinger (1887-1961)(1887-1961)
• In 1926 Schrodinger In 1926 Schrodinger gave us our modern gave us our modern mathematical mathematical description of the description of the atom:atom:
• The Quantum The Quantum Mechanical Mechanical ModelModel
Quantum MechanicsQuantum Mechanics
Quantum Mechanical Model of the Quantum Mechanical Model of the AtomAtom
• Orbitals: Regions Orbitals: Regions where where statistically statistically electrons are electrons are likely to be likely to be found. found.
• Electrons are 3 Electrons are 3 dimensional dimensional waveswaves
Radial Distribution CurveRadial Distribution Curve
OrbitalOrbital
The Quantum Mechanical The Quantum Mechanical ModelModel
• Electrons have Electrons have specific energy specific energy levels (like Bohr levels (like Bohr predicted.)predicted.)
• BUT electrons are BUT electrons are notnot in specific in specific ORBITS (unlike ORBITS (unlike what Bohr what Bohr predicted).predicted).
The QuantumThe Quantum Mechanical Mechanical ModelModel
• Determines: Determines:
Energy level-Energy level-the the allowed energies an allowed energies an electron can haveelectron can have
Atomic orbital-Atomic orbital- A A region of space region of space around the nucleus around the nucleus in which there is a in which there is a high probability of high probability of finding an electron.finding an electron.
Arrangement of Arrangement of Electrons in AtomsElectrons in Atoms
Arrangement of Arrangement of Electrons in AtomsElectrons in Atoms
• Electrons in atoms are arranged asElectrons in atoms are arranged as
• LEVELSLEVELS (n) (n)
• SUBLEVELSSUBLEVELS (l) (l)
• ORBITALSORBITALS (m (mll))
Types of OrbitalsTypes of Orbitals• The most probable area to find these The most probable area to find these
electrons takes on a shapeelectrons takes on a shape
• So far, we have 4 shapes. They are So far, we have 4 shapes. They are named s, p, d, and f. named s, p, d, and f.
• No more than 2 e- assigned to an No more than 2 e- assigned to an orbital – one spins clockwise, one orbital – one spins clockwise, one spins counterclockwisespins counterclockwise
s orbital—1 spherical -2 s orbital—1 spherical -2 electronselectrons
Relative sizes of the spherical Relative sizes of the spherical 11ss, 2, 2ss, and 3, and 3ss orbitals of orbitals of
hydrogen.hydrogen.
p-orbital-3 types-6 p-orbital-3 types-6 electronselectrons
p Orbitalsp Orbitalsp Orbitalsp Orbitals• this is a this is a p sublevelp sublevel
with with 3 orbitals3 orbitals• These are called x, y, and zThese are called x, y, and z
• this is a this is a p sublevelp sublevel with with 3 orbitals3 orbitals
• These are called x, y, and zThese are called x, y, and zplanar node
Typical p orbital
planar node
Typical p orbital
There is a There is a PLANAR NODE thru the nucleus, thru the nucleus, which is an area of zero which is an area of zero probability of finding an probability of finding an electronelectron
3py orbital
p Orbitalsp Orbitalsp Orbitalsp Orbitals
• The three p orbitals lie 90The three p orbitals lie 90oo apart in apart in spacespace
d-orbital-5 types-10 d-orbital-5 types-10 electronselectrons
d d OrbitalsOrbitalsd d OrbitalsOrbitals
• d sublevel has 5 orbitals
typical d orbital
planar node
planar node
The shapes and labels The shapes and labels of the five 3of the five 3dd orbitals. orbitals.
f-orbitals-14-electronsf-orbitals-14-electrons
f Orbitalsf Orbitalsf Orbitalsf Orbitals• For l = 3 ---> For l = 3 --->
f sublevel with f sublevel with 7 orbitals7 orbitals
Orbitals and the Periodic Orbitals and the Periodic TableTable• grouped in s, p, d, and f orbitalsgrouped in s, p, d, and f orbitals
s orbitalsp orbitals
d orbitalsd orbitals
f orbitals
Energy LevelsEnergy LevelsEnergy LevelsEnergy Levels• Each energy level has a number Each energy level has a number
called thecalled the PRINCIPAL QUANTUM PRINCIPAL QUANTUM NUMBER, nNUMBER, n
• Currently n can be 1 thru 7, Currently n can be 1 thru 7, because there are 7 periods on because there are 7 periods on the periodic tablethe periodic table
Energy LevelsEnergy LevelsEnergy LevelsEnergy Levelsn = 1n = 1
n = 2n = 2
n = 3n = 3
n = 4
Why are d and f orbitals Why are d and f orbitals always in lower energy always in lower energy
levels?levels?• d and f orbitals require LARGE d and f orbitals require LARGE
amounts of energyamounts of energy
• It’s better (lower in energy) to skip It’s better (lower in energy) to skip a sublevel that requires a large a sublevel that requires a large amount of energy (d and f orbtials) amount of energy (d and f orbtials) for one in a higher level but lower for one in a higher level but lower energyenergy
Principal Principal energy levelenergy level
Number of Number of sublevelssublevels
Type of Type of sublevelsublevel
n = 1n = 1 11 1 s (1 orbital)1 s (1 orbital)
n = 2n = 2 22 2s (1 orbital)2s (1 orbital)
2 p (3 orbital)2 p (3 orbital)
n = 3n = 3 33 3s (1 orbital)3s (1 orbital)
3p (3 orbitals)3p (3 orbitals)
3d (5 orbitals)3d (5 orbitals)
n = 4n = 4 44 4s (1 orbital)4s (1 orbital)
4p (3 orbitals)4p (3 orbitals)
4d (5 orbitals)4d (5 orbitals)
4f (7 orbitals)4f (7 orbitals)
The maximum number of electrons The maximum number of electrons that can occupy and energy level = that can occupy and energy level =
2n2n22
Energy level (n) Energy level (n) Maximum number of Maximum number of electronselectrons
11 22
22 88
33 1818
44 3232
s orbitalss orbitals d orbitalsd orbitals
Number ofNumber oforbitalsorbitals
Number of Number of electronselectrons
p orbitalsp orbitals f orbitalsf orbitals
How many electrons can be in a sublevel?How many electrons can be in a sublevel?
Remember: A maximum of two electrons can be placed in an orbital.
Electron ConfigurationsElectron Configurations
• A list of all the electrons in an atom (or ion)A list of all the electrons in an atom (or ion)• Must go in order (Aufbau principle)Must go in order (Aufbau principle)• 2 electrons per orbital, maximum2 electrons per orbital, maximum• We need electron configurations so that we can We need electron configurations so that we can
determine the number of electrons in the determine the number of electrons in the outermost energy level. outermost energy level.
• The number of valence electrons determines The number of valence electrons determines how many and what this atom (or ion) can bond how many and what this atom (or ion) can bond to in order to make a moleculeto in order to make a molecule
1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s 6s22 4f 4f1414…… etc.etc.
Electron ConfigurationsElectron Configurations
•2p2p44
Energy LevelEnergy Level
SublevelSublevel
Number of Number of electrons in electrons in the sublevelthe sublevel
1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22 3d 3d1010 4p 4p66 5s 5s22 4d 4d1010 5p 5p66 6s6s22 4f 4f1414…… etc.etc.
Three rules tell you how to find Three rules tell you how to find the electron configurations of the electron configurations of
atoms.atoms.• The Aufbau Principle—electrons occupy The Aufbau Principle—electrons occupy
the orbitals of lowest energy first.the orbitals of lowest energy first.
• Pauli Exclusion Principle—an atomic Pauli Exclusion Principle—an atomic orbital may hold at most two electrons.orbital may hold at most two electrons.
• Hund’s Rule—one electron enters orbitals Hund’s Rule—one electron enters orbitals of equal energy until all orbitals contain of equal energy until all orbitals contain one electron with the same spin direction.one electron with the same spin direction.
• Electrons Electrons fill the fill the lowest lowest energy energy orbitals orbitals first.first.
Aufbau PrincipleAufbau PrincipleAufbau PrincipleAufbau Principle
• Each orbital can Each orbital can hold TWO hold TWO electrons with electrons with opposite spins.opposite spins.
Pauli Exclusion Pauli Exclusion PrinciplePrinciple
Pauli Exclusion Pauli Exclusion PrinciplePrinciple
RIGHTWRONG
• Hund’s RuleHund’s Rule
• Within a sublevel, place one eWithin a sublevel, place one e-- per orbital before pairing them.per orbital before pairing them.
• ““Empty Bus Seat Rule”Empty Bus Seat Rule”
• Shorthand ConfigurationShorthand Configuration
S 16e-
Valence Electrons
Core Electrons
S 16e- [Ne] 3s2 3p4
1s2 2s2 2p6 3s2 3p4
NotationNotation• Longhand ConfigurationLonghand Configuration
Orbital DiagramsOrbital Diagrams• Graphical representation of an Graphical representation of an
electron configurationelectron configuration
• One arrow represents one electronOne arrow represents one electron
• Shows spin and which orbital within Shows spin and which orbital within a sublevela sublevel
• Same rules as before (Aufbau Same rules as before (Aufbau principle, dprinciple, d44 and d and d99 exceptions, two exceptions, two electrons in each orbital, etc. etc.)electrons in each orbital, etc. etc.)
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
O
8e-
• Orbital DiagramOrbital Diagram
Electron ConfigurationElectron Configuration
1s2 2s2 2p4
Notation of OxygenNotation of Oxygen
1s 2s 2p
Shorthand Shorthand NotationNotation
• A way of abbreviating long electron A way of abbreviating long electron configurationsconfigurations
• Since we are only concerned about Since we are only concerned about the outermost electrons, we can the outermost electrons, we can skip to places we know are skip to places we know are completely full (noble gases), and completely full (noble gases), and then finish the configurationthen finish the configuration
Shorthand Shorthand NotationNotation
• Step 1: Find the closest noble gas to Step 1: Find the closest noble gas to the atom (or ion), WITHOUT GOING the atom (or ion), WITHOUT GOING OVER the number of electrons in the OVER the number of electrons in the atom (or ion). Write the noble gas in atom (or ion). Write the noble gas in brackets [ ].brackets [ ].
• Step 2: Find where to resume by Step 2: Find where to resume by finding the next energy level.finding the next energy level.
• Step 3: Resume the configuration until Step 3: Resume the configuration until it’s finished.it’s finished.
Shorthand Shorthand NotationNotation• ChlorineChlorine
• Longhand is Longhand is 1s2 2s2 2p6 3s2 3p5
• You can abbreviate the first 10 electrons You can abbreviate the first 10 electrons with a noble gas, Neon. [Ne] replaces with a noble gas, Neon. [Ne] replaces 1s2 2s2 2p6
• The next energy level after Neon is 3The next energy level after Neon is 3• So you start at level 3 (all levels start with So you start at level 3 (all levels start with
s) and finish the configuration by adding 7 s) and finish the configuration by adding 7 more electrons to bring the total to 17more electrons to bring the total to 17
• [Ne] 3s[Ne] 3s22 3p 3p55
Exceptions to the Aufbau Exceptions to the Aufbau PrinciplePrinciple• dd44 is one electron short of being HALF full is one electron short of being HALF full• In order to become more stable (require less In order to become more stable (require less
energy), one of the energy), one of the closest sclosest s electrons will electrons will actually go into the d, making it dactually go into the d, making it d55 instead of instead of dd44..
• For example: Cr would be [Ar] 4sFor example: Cr would be [Ar] 4s22 3d 3d44, but , but since this ends since this ends exactlyexactly with a d4 it is an with a d4 it is an exception to the rule. Thus, Cr should be [Ar] exception to the rule. Thus, Cr should be [Ar] 4s4s11 3d 3d55..
• Procedure: Find the closest s orbital. Steal Procedure: Find the closest s orbital. Steal one electron from it, and add it to the d.one electron from it, and add it to the d.
Exceptions to the Aufbau Exceptions to the Aufbau PrinciplePrinciple• OK, so this helps the d, but what about OK, so this helps the d, but what about
the poor s orbital that loses an the poor s orbital that loses an electron?electron?
• Remember, half full is good… and when Remember, half full is good… and when an s loses 1, it too becomes half full!an s loses 1, it too becomes half full!
• So… having the s half full and the d So… having the s half full and the d half full is usually lower in energy than half full is usually lower in energy than having the s full and the d to have one having the s full and the d to have one empty orbital.empty orbital.