The two electrons in the outermost level of strontium are designated as 5s 2. 
How many quantum numbers would these two electrons have in common?
a. 1   b. 4    c. 3

Hi teatea!!

The correct answer is c) 3.

It cannot be 4 quantum numbers in common, because the four numbers
define completely an individual electron in the atom and the Pauli
exclusion principle says no to have two electrons with the same four
numbers.

So it must be 1 or 3. :>))

Take a look to the quantum numbers:
1. Principal (shell) quantum number - n 
 Describes the energy level within the atom. 

2. Momentum (subshell) quantum number - l
 Describes the sublevel in n 
 Sublevels in the atoms of the known elements are s - p - d - f 
 Each energy level has n sublevels. 
 Sublevels of different energy levels may have overlapping energies.

3. Magnetic quantum number - m 
 Describes the orbital within a sublevel 
  s has 1 orbital 
  p has 3 orbitals 
  d has 5 orbitals 
  f has 7 orbitals 
 Orbitals contain 1 or 2 electrons, never more. 
 The magnetic quantum number (m) can be any integer from minus l up to
l.

4. Spin quantum number - s 
 This fourth quantum number describes the spin of the electron. 
 Electrons in the same orbital must have opposite spins. 
 Possible spins are clockwise or counterclockwise.

Pauli Exclusion Principle: 
 No two electrons in an atom have the same set of four quantum
numbers.


When we designate the two electrons in the outermost level of
strontium as 5s2, we are saying the following:
- Both electrons have principal number 5.
- Both electrons have momentum s (l = 0).
- Both electrons have magnetic number m = 0; because l =0. 

The fourth number (spin) must be different because the Pauli Exclusion
Principle, so the two electrons in the outermost level of strontium
designated as 5s2 have 3 quantum numbers in common.

For more info see the following pages:
From Chemistry classes of The Science Room site, "Quantum Numbers"
page:
http://www.howe.k12.ok.us/~jimaskew/cquantum.htm


From "Physics 2000" a University of Colorado at Boulder website:
"The Pauli Exclusion Principle":
http://www.colorado.edu/physics/2000/elements_as_atoms/electron_config.html

"Quantum Numbers", follow the NEXT link:
http://www.colorado.edu/physics/2000/elements_as_atoms/quantum_numbers.html
 
After read this pages you can navigate the site with the NEXT and
PREVIOUS links.


Search strategy:
Pauli exclusion principle
quantum numbers


Hope this helps.

Regards.
livioflores-ga