chapter 7; electronic structure of atoms i.electromagnetic radiation ii.flame test/ emission spectra...
TRANSCRIPT
Chapter 7; Electronic Structure of Atoms
I. Electromagnetic Radiation
II. Flame Test/ Emission Spectra
III. Quantized Energy Levels
IV. Bohr Model/ Rydberg Equation
V. Principal Energy Levels, na) First Ionization Energy
b) 2nd , 3rd, 4th, etc Ionization Energy
Chapter 7; Electronic Structureof Atoms
VI. Sublevels (s, p, d, f)a) Photoelectron Spectroscopy
VII. Electron ConfigurationVIII. Valence Electrons/ CoreIX. Good/ Bad Point of Atom ModelX. Quantum Theory
a) Dual Nature of the Electronb) Heisenberg Uncertainty Principle
Chapter 7; ElectronicStructure of Atoms
XI. Quantum Numbers (n, l, ml, ms)
XII. Oribtal Diagramsa) Paramagnetism and Diamagnetism
Electronic Structure Model
Experimental Evidence1. Line Spectra
2. Ionization Energies
3. Photoelectron Spectrum
4. Intensity/detail of Line Spectra
What it means1. Electrons in quanitized ‘n’
2. # electrons in each ‘n’
3. # electrons in each ‘n’ and each sublevel
4. Indicates ‘n’ have sublevels associated with them
Electronic Structure
n # of Sublevel
# e- in n
(2n2)
Sublevel
Names
# e- in each sublevel
1 1 2 s s-2
2 2 8 s,p s-2, p-6
3 3 18 s,p,d s-2, p-6,
d-10
4 4 32 s,p,d,f s-2, p-6,
d-10, f-14
Order of orbitals (filling) in multi-electron atom
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s7.7
What is the electron configuration of Mg?
Mg 12 electrons
1s < 2s < 2p < 3s < 3p < 4s
1s22s22p63s2 2 + 2 + 6 + 2 = 12 electrons
7.7
Abbreviated as [Ne]3s2 [Ne] 1s22s22p6
What is the electron configuration of Cl?
Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s
1s22s22p63s23p5 2 + 2 + 6 + 2 + 5 = 17 electrons
Electron Configurations of Cations and Anions
Na [Ne]3s1 Na+ [Ne]
Ca [Ar]4s2 Ca2+ [Ar]
Al [Ne]3s23p1 Al3+ [Ne]
Atoms lose electrons so that cation has a noble-gas outer electron configuration.
H 1s1 H- 1s2 or [He]
F 1s22s22p5 F- 1s22s22p6 or [Ne]
O 1s22s22p4 O2- 1s22s22p6 or [Ne]
N 1s22s22p3 N3- 1s22s22p6 or [Ne]
Atoms gain electrons so that anion has a noble-gas outer electron configuration.
Of Representative Elements
8.2
Na+: [Ne] Al3+: [Ne] F-: 1s22s22p6 or [Ne]
O2-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne]
Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne
What neutral atom is isoelectronic with H- ?
H-: 1s2 same electron configuration as He
8.2
Electron Configurations of Transition Metals
• Completely filled or half-completely filled d-orbitals have a special stability
– Some “irregularities” are seen in the electron configurations of transition and inner-transition metals.
Electron Configurations of Cations of Transition Metals
8.2
When a cation is formed from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n – 1)d orbitals.
Fe: [Ar]4s23d6
Fe2+: [Ar]4s03d6 or [Ar]3d6
Fe3+: [Ar]4s03d5 or [Ar]3d5
Mn: [Ar]4s23d5
Mn2+: [Ar]4s03d5 or [Ar]3d5
Order of filling; 3s<3p<4s<3dBut when removing electrons to form + ions for transition metalsOrder of removing electrons; 4s<3d<3p<3s
Electronic Structure
Good Points• Electrons in Quantized
Energy Levels• Maximum # electrons
in each n is 2n2
• Sublevels (s,p,d,f) and # electrons they hold
Bad Points• Electrons are placed in
orbits about nucleus• Only explains
emission spectra of H2
• Does not address all interactions
• Treats electron as particle
H
+1
Be
+4
There are less interactions to take into account in H than other elements
Interactions1. Attraction between + nucleus and negative electrons
Interactions1. Attraction between + nucleusand negative electrons2. Repulsion between electronsin same energy level.3. Shielding effect of filledprincipal energy levels.
Quantum Theory – Revised Electronic Structure Model
1. Dual Nature of the Electron
2. Heisenberg Uncertainty Principle
Dual Nature of Electron
Previous Concept;
A Substance is Either Matter or Energy
• Matter; Definite Mass and Position
Made of Particles
• Energy; Massless and Delocalized
Position not Specificed
Wave-like
Dual Nature of Electron
• Electron is both “particle-like” and “wave-like” at the same time.
• Previous model only considered “particle-like” nature of the electron
Heisenberg Uncertainty Principle
• Act of measuring the position and energy of electron changes the position of electron
– Better one variable is known (energy); the less well the other variable is known (position)
Orbitals Replace Orbits
• Orbits- Both electron position and energy known with certainty
• Orbitals – Regions of space where an electrons of a given energy will most likely be found
Quantum TheoryOrbitals Replace Orbits
Orbits Orbitals
Schrodinger Wave Equation ()
Describes size/shape/orientation of orbitals
7.5
• Wave Equation is based on…
1. Dual Nature of Electron (Electron both particle and wave-like at the same time.)
2. Heisenberg Uncertainty Principle(Orbitals describe a region in space an electron will most likely be.)
Wave Equation ()
• Wave Equation describe the size, shape, and orientation of the orbital the electron (of a given energy) is in. There are four variables in the function
-n; Energy and size of orbital– l; Shape of orbital
– ml; Orientation of orbital
– ms; Electron Spin
(n, l, ml, ms)
1. Each electron has a unique set of 4 Quantum Numbers
2. Each orbital described by the Quantum Numbers can hold a maximum of 2 electrons.
Schrodinger Wave Equation;1st Quantum Number
fn(n, l, ml, ms)
principal quantum number n
n = 1, 2, 3, 4, ….
n=1 n=2 n=3
7.6
distance of e- from the nucleus
= fn(n, l, ml, ms)
angular momentum quantum number l
for a given value of n, l = 0, 1, 2, 3, … n-1
n = 1, l = 0n = 2, l = 0 or 1
n = 3, l = 0, 1, or 2
Shape of the “volume” of space that the e- occupies
l = 0 s orbitall = 1 p orbitall = 2 d orbitall = 3 f orbital
Schrodinger Wave Equation2nd Quantum Number
7.6
Principal Energy Level, n
Sublevel,
l
Quantum # Electron Configuration
1 0 (1,0, , ) 1s
2 0 (2,0, , ) 2s
1 (2, 1, , ) 2p
3 0 (3,0, , ) 3s
1 (3, 1, , ) 3p
2 (3,2, , ) 3d
4 0 (4,0, , ) 4s
1 (4, 1, , ) 4p
2 (4, 2, , ) 4d
3 (4, 3, , ) 4f
l = 0 (s orbitals)
l = 1 (p orbitals)
7.6
l = 2 (d orbitals)
f-orbitals
Orbital Shapes
Orbital Type Shape Name
s Spherical
p Dumbbell
d Complex
f More complex
= fn(n, l, ml, ms)
magnetic quantum number ml
for a given value of lml = -l, …., 0, …. +l
orientation of the orbital in space
if l = 1 (p orbital), ml = -1, 0, or 1if l = 2 (d orbital), ml = -2, -1, 0, 1, or 2
Schrodinger Wave Equation3rd Quantum Number
7.6
Number of Degenerate Orbitals Needed for Each Type of Orbital (Sublevel)
Type of Orbital Maximum # of electrons in
Orbital
# of Degenerate Orbitals
s 2 1
p 6 3
d 10 5
f 14 7
ml = -1 ml = 0 ml = 1
ml = -2 ml = -1 ml = 0 ml = 1 ml = 2
= fn(n, l, ml, ms)
spin quantum number ms
ms = +½ or -½
Schrodinger Wave Equation4th Quantum Number
ms = -½ms = +½
7.6
Valid Possibilities for Quantum Numbers
Chemistry; The Science in Context; by Thomas R Gilbert, Rein V Kriss, and Geoffrey Davies, Norton Publisher, 2004, p125
How many 2p orbitals are there in an atom?
2p
n=2
l = 1
If l = 1, then ml = -1, 0, or +1
3 orbitals
How many electrons can be placed in the 3d subshell?
3d
n=3
l = 2
If l = 2, then ml = -2, -1, 0, +1, or +2
5 orbitals which can hold a total of 10 e-
7.6
Three Manners to Convey How Electrons are Arranged
1. Electron Configuration ; List Orbitals and Number of Electrons in Each
(1s22s22p63s2…)
2. Quantum Numbers (2,0,0,+1/2)
3. Orbital Diagrams; List Orbitals and show location of electrons and their spin
1s 2s 2p
Pauli exclusion principle - no two electrons in an atomcan have the same four quantum numbers.
The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule)or maximum # of unpaired electrons.
Orbital Diagrams
7.7
Orbital Diagrams
1s 2s 2p
Carbon; 6 electrons
Electron Configuration; 1s22s22p2
Orbital Diagram
Orbital Diagrams
1s 2s 2p
Oxygen; 8 electrons
Electron Configuration; 1s22s22p4
Orbital Diagram
Paramagnetic
unpaired electrons
2p
Diamagnetic
all electrons paired
2p7.8