Electron Orbitals Cartoon courtesy of lab-initio.com
The Bohr Model of the Atom I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive.Neils Bohr
DeBroglie Model- Since light waves canhave a particle behavior(as shown by Einstein),then it follows thatparticles could exhibit awave behavior.- Saw the electron as awave.
Schrodinger and His Cat•First to propose the idea of electron duality.•Proposed classic thought experiment involving acat in a box.•The electron is simultaneously a particle and awave but cannot be observed in this state. -When you observe it the electron adopts one state or the other.
Heisenberg Uncertainty Principle “One cannot simultaneously determine both the position and momentum of an electron.” You can find out where the electron is, but not where it is going. OR… You can find out where the Werner electron is going, but notHeisenberg where it is!
Quantum Mechanical Model of the AtomMathematical laws can identify theregions outside of the nucleuswhere electrons are most likely tobe found.These laws are beyond the scope ofthis class…
Quantum Mechanical Model of the Atom•As in the the deBroglie and Bohr Models theelectrons energy is quantized into distinctlevels. •As the atom is excited electrons move into higher levels (further from nucleus) and vice versa.•The Quantum Mechanical model, however,makes no attempt to predict the path of theelectron (Heisenburg). •It does define the electrons most probable location based on a set of rules.
Levels of Organization •The Quantum Mechanical model still relies on the idea of quantized energy levels HOWEVER each energy level is further subdivided into probability zones. oCalled Orbitals oThe larger the energy level the more probability zones it can contain. You add a new set of orbitals with each successive energy level.
Four Quantum Numbers• The Quantum Mechanical Model describes the location of each electron based upon successive levels of organization called Quantum Numbers. 1. Principal Quantum Number 2. Orbital Quantum Number 3. Magnetic Quantum Number 4. Spin Quantum Number• Each electron within the atom is assigned a unique combination of quantum numbers based upon the location of it’s electrons – The 4 quantum numbers provide the specific location of each electron. Similar to an address.
Electron Energy Levels (Shell)•First level of organization. •Similar to Bohr Model.•The shell denotes the probabledistance of the electron from thenucleus.•Principle Quantum Number (N): •Indicates the relative size and energy of a shell. •Denoted as “N” •As N increases the energy level becomes larger and the electron spends more time farther from the nucleus.•Not evenly spaced.
# of Electrons in Energy LevelsThe larger the shell themore electrons it can hold. Maximum # of electrons per shellAs “N” increases so does the 1st shell: 2maximum number of electrons 2nd shell: 8that can be in the shell. 3rd shell: 18 Number of electrons 4th shell: 32 that can fit in a 5th shell: 50 shell: 2n 2
Orbital Sub-Levels PRINCIPAL SUB LEVELS ENERGY LEVELS 4 •Each main energy level (shell)INCREASING ENERGY / DISTANCE FROM NUCLEUS can be subdivided into sublevels. •Level 1 was split into 1 sub level 3 •Level 2 was split into 2 sub levels •Level 3 was split into 3 sub levels •Level 4 was split into 4 sub levels 2 •These sublevels are known as orbitals. 1
Orbital Quantum Number, ℓ (Angular Momentum Quantum Number)Indicates shape of orbital sublevels ℓ = n-1 ℓ sublevel 0 s 1 p 2 d 3 f 4 g
Orbital ShapeScientists calculate the shape of orbitalsbased upon probability.Orbital Shapes are defined as the surfacethat contains 90% of the total electronprobability.
ℓ = 0 or S Orbital shape•Each energy levelcontains onespherical S-Orbital•Holds 2 Electrons
ℓ = 1 or P Orbitals shape•There are 3 dumbbell-shaped p orbitalsbeginning in n = 2•Each assigned to itsown axis (x, y and z) inspace.•Each P orbital containstwo electrons. 2 x 3 = 6 Total
ℓ = 2 or D Orbitals shape Things get a bit more complicated with the five d orbitals beginning in n = 3. 5 x 2 = 10 Electrons Total To remember the shapes, think of “double dumbells” …and a “dumbell with a donut”!
ℓ = 3 or f Orbitals shapeBeginning in N=4 there are 7 f-orbitals. 7 x 2 = 14 Electrons Total
Energy Levels, Orbitals, ElectronsEnergy Orbital type Number of Number of Number of Level in the orbitals Electrons electrons per (n ) energy level Energy level (types = n) (2n2) 1 s 1 2 2 2 s 1 2 8 p 3 6 3 s 1 2 18 p 3 6 d 5 10 4 s 1 2 32 p 3 6 d 5 10 f 7 14
Magnetic Quantum Number, mlIndicates the orientation of the orbital in space.Values of ml : integers -ℓ to +ℓThe number of values represents the number of orbitals.Example: for ℓ= 2, ml = -2, -1, 0, +1, +2 Which sublevel does this represent? Answer: d
Electron Spin (ms or s)Electron spin describes the behavior(direction of spin: clockwise orcounterclockwise) of an electronwithin a magnetic field.Establishes a limit of 2 electrons per orbitalPossibilities for electron spin: 1 1 OR 2 2
Quantum Mechanical Model Summary Electrons are located in specific energy levels. There is no exact path around the nucleus. The model estimates the probability of finding an electron in a certain position.
QUANTUM NUMBERSn ---> energy level or shell 1, 2, 3, 4, ...ℓ ---> subshell or orbitals 0, 1, 2, ... n – 1ml ---> magnetic orientation -ℓ ... 0 ... +ℓms ---> electron spin +1/2 and -1/2
Rules for Filling The Diagram• Aufbau Principle: Electrons will fill the lowest energy levels subshell first before moving to the next higher level. – The Concert Rule• Hunds Rule: The most stable arrangement of electrons is that with the maximum number of unpaired electrons, all with the same spin direction. (Electrons won’t double up if they don’t have to, as long as they don’t violate the Aufbau Principle) – The Urinal Etiquette Rule• Pauli Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers. (Only 2 electrons can be in an orbital and they must have opposite spins) – Two is Company, but Three is a Crowd Rule