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Transcript of Chapter 09 Tro Rev 1
8/3/2019 Chapter 09 Tro Rev 1
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Tro's Introductory Chemistry, Chapter 9 2
Why do Blimps Float?
Because they are filled with agas less dense than air
Early blimps used hydrogen gas; hydrogen’s flammabilityled to the Hindenburg disaster
Blimps now use helium, anonflammable gas – in fact itdoesn’t undergo any chemicalreactions
This chapter investigatesmodels of the atom we use toexplain the differences in theproperties of the elements
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Tro's Introductory Chemistry, Chapter 9 3
Electromagnetic Radiation
Light is one of the forms ofenergy
Light is one type of a moregeneral form of energycalled electromagnetic radiation
Electromagnetic radiationtravels in waves
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Tro's Introductory Chemistry, Chapter 9 4
Characteristics of a Wave
Wavelength = distance from peak to peak
Amplitude = height of the peak
Frequency = the number of wave peaks thatpass in a given time
Speed = rate the waves travel
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Tro's Introductory Chemistry, Chapter 9 5
Particles of Light
Scientists in the early 20th century showedthat electromagnetic radiation was composedof particles we call photons
– Max Planck and Albert Einstein
– photons are particles of light energy
Each wavelength of light has photons thathave a different amount of energy
– the longer the wavelength, the lower theenergy of the photons
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Tro's Introductory Chemistry, Chapter 9 6
The Electromagnetic Spectrum
Light passed through a prism is separated intoall its colors = continuous spectrum ; colors blend into each other
Color of light is determined by its wavelength
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Tro's Introductory Chemistry, Chapter 9 8
Light’s Relationship to Matter
Atoms can absorb energy, butthey must eventually release it
When atoms emit energy, it is
released in the form of light =emission spectrum
Atoms don’t absorb or emit all
colors, only very specific
wavelengths; the spectrum ofwavelengths can be used toidentify the element
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Tro's Introductory Chemistry, Chapter 9 9
Emission Spectrum or Line Spectrum
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Tro's Introductory Chemistry, Chapter 9 10
Line Spectra = specific wavelengths areemitted; characteristic of atoms
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Tro's Introductory Chemistry, Chapter 9 11
The Bohr Model of the Atom
Nuclear Model of atom does not explain howatom can gain or lose energy
Neils Bohr developed a model to explain howstructure of the atom changes when itundergoes energy transitions
Bohr postulated that energy of the atom wasquantized , and that the amount of energy in the
atom was related to the electron’s position inthe atom – quantized means that the atom could only have very
specific amounts of energy
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12
Bohr Model of Atom: Electron Orbits
In the Bohr Model, electrons travel in orbitsor energy levels around the nucleus
The farther the electron is from the nucleusthe more energy it has
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Tro's Introductory Chemistry, Chapter 9 13
The Bohr Model of the Atom:Orbits and Energy
Each orbit (energy level) has aspecific amount of energy
Energy of each orbit issymbolized by n , with values of1, 2, 3 etc; the higher the valuethe farther it is from the
nucleus and the more energyan electron in that orbit has
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Tro's Introductory Chemistry, Chapter 9 14
The Bohr Model of the Atom:Energy Transitions
Electrons can move froma lower to a higher(farther from nucleus)
energy level by absorbingenergy
When the electron movesfrom a higher to a lower
(closer to nucleus)energy level, energy isemitted from the atom asa photon of light
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Tro's Introductory Chemistry, Chapter 9 15
The Bohr Model of the AtomGround and Excited States
Ground state – atoms with their electrons inthe lowest energy level possible; this lowestenergy state is the most stable.
Excited state – a higher energy state;electrons jump to higher energy levels byabsorbing energy
Atom is less stable in an excited state; it willrelease the extra energy to return to theground state
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Tro's Introductory Chemistry, Chapter 9 16
Electron Energy Levels:
Energy Level How many e fit? (2n2
)3rd 18 electrons 2 x 32
2nd 8 electrons 2 x 22
1st
2 electrons 2 x 12
Each energy level has a maximum # ofelectrons it can hold.
H has one electron; it is in the 1st
energy level.
H Bohr model
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Tro's Introductory Chemistry, Chapter 9 17
Bohr Model for AtomElectrons fill the Lowest energy levels first
C
Bohr Model for C with 6 electrons
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Tro's Introductory Chemistry, Chapter 9 18
The Bohr Model of the AtomSuccess and Failure
The Bohr Model very accuratelypredicts the spectrum of hydrogen
with its one electronIt is inadequate when applied to atomswith many electrons
A better theory was needed
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Tro's Introductory Chemistry, Chapter 9 19
The Quantum-Mechanical ModelOrbitals
Erwin Schrödinger used mathematics topredict probability of finding an electron at acertain location in the atom
Result is a map of regions in the atom thathave a particular probability for finding theelectron
Orbital = a region with a very high probabilityof finding the electron when it has aparticular amount of energy
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Tro's Introductory Chemistry, Chapter 9 20
The Quantum-Mechanical Model
Each principal energy level or shell has one ormore subshells
– # of subshells same as the principal quantum
number or shell The subshells are often represented as aletter
– s, p, d, f
Each kind of subshell has orbitals with aparticular shape
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Tro's Introductory Chemistry, Chapter 9 21
Shells & Subshells
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Tro's Introductory Chemistry, Chapter 9 22
Probability Maps & Orbital Shapes orbitals are spherical
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Tro's Introductory Chemistry, Chapter 9 23
Probability Maps & Orbital Shape
p orbitals
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Tro's Introductory Chemistry, Chapter 9 24
Subshells and Orbitals
The subshells of a principal shell haveslightly different energies
– the subshells in a shell of H all have the sameenergy, but for multielectron atoms the subshells
have different energies – s < p < d < f
Each subshell contains one or more orbitals
– s subshells have 1 orbital
– p subshells have 3 orbitals
– d subshells have 5 orbitals
– f subshells have 7 orbitals
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Tro's Introductory Chemistry, Chapter 9 25
The Quantum Mechanical ModelEnergy Transitions
As in Bohr Model, atoms gain or loseenergy as electron moves betweenorbitals in different energy shells and
subshells
The ground state of the electron is thelowest energy orbital it can occupy
Excited state = when an electron movesto a higher energy orbital
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Tro's Introductory Chemistry, Chapter 9 26
The Bohr Model vs.The Quantum Mechanical Model
Both the Bohr and QuantumMechanical models predict the
spectrum of hydrogen very accurately
Only the Quantum Mechanical modelpredicts the spectra of multielectron
atoms
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Tro's Introductory Chemistry, Chapter 9 27
Electron Configurations
Electron configuration = distribution ofelectrons into the various energy shellsand subshells in an atom in its groundstate
Each energy shell and subshell has amaximum number of electrons it canhold
– s = 2 , p = 6, d = 10, f = 14
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Tro's Introductory Chemistry, Chapter 9 28
Writing Electron Configurations
We place electrons in the energyshells and orbitals in order ofenergy, from low energy up: AufbauPrinciple (order of filling of orbitals)
The d and f orbitals overlap into the
higher energy levels
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Tro's Introductory Chemistry, Chapter 9 29
E n e r g y
1s
7s
2s
2p
3s
3p
3d
6s6p
6
d
4s
4p
4d4f
5s
5p
5d5f
Relative Energy of Orbitalsin the Quantum Mechanical Model
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Tro's Introductory Chemistry, Chapter 9 30
Order of Subshell Fillingin Ground State Electron Configurations
1s
2s 2 p
3s 3 p 3d
4s 4 p 4d 4 f
5s 5 p 5d 5 f
6s 6 p 6d
7s
Start by drawing a diagram
putting each energy shell on
a row and listing the subshells,
(s, p, d, f ), for that shell inorder of energy, (left-to-right)
next, draw arrows through
the diagonals, looping back
to the next diagonal
each time
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Tro's Introductory Chemistry, Chapter 9 31
Filling the Orbitals in a Subshellwith Electrons
Energy shells fill from lowest energy to high
Subshells fill from lowest energy to high
– s → p → d → f
A single orbital can hold a maximum of 2electrons (Pauli’s exclusion principle); orbitals
that are in the same subshell have the same
energyWhen filling orbitals that have the same energy,place one electron in each before completing
pairs (Hund’s rule)
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Tro's Introductory Chemistry, Chapter 9 32
Electron Configuration of Atomsin their Ground State
Electron configuration = order of filling withelectrons; number of electrons in that subshellwritten as a superscript
Kr = 36 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 6 Shorthand way: use the symbol of the previousnoble gas in brackets to represent all the innerelectrons, then just write the last set
Rb = 37 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 65s 1 =[Kr]5s 1
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Tro's Introductory Chemistry, Chapter 9 33
Electron Configurations
Nitrogen: 1s2
2s2
2p3
(atomic number = 7)
energy level orbital
how many electronsin that orbital
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Tro's Introductory Chemistry, Chapter 9 34
1. Determine the atomic number of the
element from the Periodic Table – This gives the number of protons and
electrons in the atom
Mg, Z = 12, so Mg has 12 protons and 12electrons
Example – Write the Ground StateOrbital Diagram and Electron
Configuration of Magnesium.
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Tro's Introductory Chemistry, Chapter 9 35
2. Draw 9 boxes to represent the first 3
energy levels s and p orbitals
1s 2s 2p 3s 3p
Example – Write the Ground StateOrbital Diagram and Electron
Configuration of Magnesium.
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Tro's Introductory Chemistry, Chapter 9 36
3. Add one electron to each box in a set,then pair the electrons before going tothe next set until you use all theelectrons
• When pairing, put in opposite arrows
1s 2s 2p 3s 3p
Example – Write the Ground StateOrbital Diagram and Electron
Configuration of Magnesium.
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Tro's Introductory Chemistry, Chapter 9 37
Example – Write the Ground StateOrbital Diagram and Electron
Configuration of Magnesium.
4. Use the diagram to write the electronconfiguration
– Write the number of electrons in each setas a superscript next to the name of theorbital set
1s 22s 22p 63s 2 = [Ne]3s 2
1s 2s 2p 3s 3p
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Tro's Introductory Chemistry, Chapter 9 38
Valence Electrons
Valence electrons = electrons in all thesubshells with the highest principalenergy shell (outermost shell)
Core electrons = in lower energy shells
Valence electrons responsible for bothchemical and physical properties of
atoms.Valence electrons responsible forchemical reactions
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Tro's Introductory Chemistry, Chapter 9 39
Valence Electrons
Rb = 37 electrons =1s 22s 22p 63s 23p 64s 23d 104p 65s 1
The highest principal energy shell of Rb thatcontains electrons is the 5th, therefore Rb
has 1 valence electron and 36 core electrons
Kr = 36 electrons = 1s 22s 22p 63s 23p 64s 23d 104p 6
The highest principal energy shell of Kr that
contains electrons is the 4th
, therefore Kr has8 valence electrons and 28 core electrons
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Tro's Introductory Chemistry, Chapter 9 40
How many valence electronsdoes each atom have?
carbon: 1s
2
2s
2
2p
2
chlorine: 1s22s22p63s23p5
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Tro's Introductory Chemistry, Chapter 9 41
How many valence electrons
does each atom have?
carbon: 1s
2
2s
2
2p
2
= 4
chlorine: 1s22s22p63s23p5 = 7
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Tro's Introductory Chemistry, Chapter 9 42
Electron Configurations andthe Periodic Table
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Tro's Introductory Chemistry, Chapter 9 43
Electron Configurations fromthe Periodic Table
Elements in the same period (row) havevalence electrons in the same principalenergy shell
The number of valence electrons increasesby one as you progress across the period
Elements in the same group (column) have
the same number of valence electrons andthey are in the same kind of subshell
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Tro's Introductory Chemistry, Chapter 9 44
Electron Configuration & thePeriodic Table
Elements in the same column havesimilar chemical and physical
properties because their valence shell electron configuration is the same
The number of valence electrons for
the main group elements is the same as the group number
Th E l P f
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Tro's Introductory Chemistry, Chapter 9 45
The Explanatory Power ofthe Quantum-Mechanical Model
The properties of the elements arelargely determined by the number of
valence electrons they containSince elements in the same columnhave the same number of valence
electrons, they show similar properties
Th N bl G
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The Noble GasElectron Configuration
The noble gases have 8 valenceelectrons
–
except for He, which has only 2 electronsNoble gases are especially unreactive
– He and Ne are practically inert
Reason noble gases are unreactive is
that the electron configuration of thenoble gases is especially stable