Electron Orbitals

Cartoon courtesy of lab-initio.com

The Bohr Model of the Atom

Neils Bohr

I pictured electrons orbiting the nucleus much like planets orbiting the sun.

But I was wrong! They’re more like bees around a hive.

Quantum MechanicalModel of the Atom

Mathematical laws can identify the regions outside of the nucleus where electrons are most likely to be found.

These laws are beyond the scope of this class…

Heisenberg Uncertainty Principle

You can find out where the electron is, but not where it is going.

OR…

You can find out where the electron is going, but not where it is!

“One cannot simultaneously determine both the position and momentum of an electron.”

WernerHeisenberg

Modern Quantum Theory

As a direct result of Schrondinger’s equation, the first 3 quantum numbers were derived to show properties of –e in specific orbitals in which they are located in

These equations paved the way for quantum theory describing mathematically wave properties of the –e and other small particles

First 3 Quantum Numbers describe

1- main energy level2-shape of orbital3- orientation of orbital4th quantum number describes state of –e occupying the orbital (spin number)

#1- Principle QN-n(main energy level)

Value-positive only- 1, 2, 3… 7

-e whose n=1 occupies lowest energy level (closest to the nucleus)

Total number of orbitals existing in a shell (energy level) =n2

All main energy levels has sublevels (suborbitals) of different shapes

Electron Energy Level (Shell)

Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. “n” is also known as the Principle Quantum numberNumber of electrons that can fit in a shell:2n2

Orbital shapes are defined as the surface that contains 90% of the total electron probability.

An orbital is a region within an energy level where there is a probability of finding an electron.

Electron Orbitals

#2- Angular Momentum-l

(shape of orbital)Also known as azimuthal QN

For specific energy level, the number of sublevels possible =n

Value of 0 and all positive integers less than or equal to n-1Examples:

n=2, 2 shapes l=0 represents sl=1 represents p

More about shapess orbital- n=1- spherep orbital- n=2- dumbelld- complexf- too complicated to discuss

The s orbital has a spherical shape centered aroundthe origin of the three axes in space.

s Orbital shape

There are three dumbbell-shaped p orbitals in each energy level above n = 1, each assigned to its own axis (x, y and z) in space.

p orbital shape

More QN and shapes1st energy level, n=1- only s orbital

2nd energy level, n=2- only s and p

3rd energy level, n=3- s, p and d

4th energy level, n=4- s,p,d and f

Things get a bit more complicated with the five d orbitals that are found in the d sublevels beginning with n = 3. To remember the shapes, think of “double dumbells”…and a “dumbell with a donut”!

d orbital shapes

Shape of f orbitals

#3- Magnetic QN-m1 s orbital-spherical only-

1 orientation (m=0)

3 p orbitals-3 orientations x,y,z (m= -1, m= 0, m=

1) and so on for d and f

5 d orbitals- orientation has values of m= -2, m= -1, m= 0, m= 1, m=2 representing dx2-y3,dxy, dzy, dxz, dz2

7 f orbitals-number of orbitals in each energy level equals n2

If n=1, n2=1 or if n=3 then n2=9, etc

more

#4- Spin QNValue +1/2 or –1/2

Indicates fundamental spin state of the –e (-e spin on axis in one of two directions or states)

Spin creates a magnetic field and accounts for the magnetic

properties of –e(remember cathode ray and

magnet)

WRITING QN

Each orbital show by its principle QN followed by letter of suborbital1s or 3p or 4d

Orbital filling table

Electron configuration of the elements of the first three

series