Some key scientists in development of Periodic Table of the Elements
Dmitri Mendeleev
1834-1907
First Periodic Table of elements
Henry Moseley
1887-1915
Elements are ordered
by atomic number Z
Atomic Number is
equal to number of
protons in the
nucleus.
Wolfgang Pauli
1900-1958
All electrons in an atom
have unique set of
quantum numbers.
Proposed 4th quantum
number for SPIN
Periodic Table
(Chemist)
Periodic Table
(Cosmologist)
Metals
Metals
Calculated Atomic Radii (picometers)
E. Clementi, D. L. Raimondi, and W. P. Reinhardt (1967), Journal of Chemical Physics, volume 47, page 1300
http://chemistry.about.com/library/weekly/aa013103a.htm
n
l
Nobel gases
He (1s)2
Ne (1s)2(2s)2(2p)6
Ar (1s)2(2s)2(2p)6(3s)2(3p)6
Etc
Chemically Inert
Periodic Table
(Quantum Mechanic)
Periodic Table
for the quantum mechanic
0
1
2
3
Periodic Table
Width of each box is
2(2l+1)
combinations of ml and ms for given l
s (l=0)
p (l=1)
1
2
2
d (l=2)
3
4
3
5
4
6
5
3
7
4
f (l=3)
5
On-Line Interactive Periodic Table
http://www.ptable.com/
Stern Gerlach Experiment (1922)
Expected Result for l=1 state
Stern and Gerlach used atoms that they expected were in an
l=1 state.
Due to space quantization, atoms will be deflected by non-uniform magnet
by discrete amounts corresponding to allowed values of
Lz where Lz=mlħ and for l=1 ml=-1,0,1
So they expected to see 2l+1=3 images on screen corresponding to
ml=-1,0,1
Stern Gerlach Experiment (1922)
What they actually observed
Actual Result (Image on Screen)
A
Magnet OFF
Magnet ON
Stern Gerlach Experiment (1922)
What they actually observed
Actual Result (Image on Screen)
A
Magnet OFF
Magnet ON
Explaination:
They did see space quantization effect.
But actually the atoms they were using were in a l=0 state
They saw the space quantization of the intrinsic orbital momentum (spin)
Sz where Sz=msħ and ms=-1/2,+1/2
Two possible values for Sz so separation to 2 region
Stern Gerlach Experiment
how spins behave in magnetic fields
Spin is quantized
• For electrons (& other fermions), spin can only take
on two values: up ↑ or down ↓.
• What’s so special about the z-axis?
– Answer: nothing.
• Can measure spin along any axis, will always find spin
either aligned or anti-aligned with the axis you
measure along.
• Just like position and momentum, spin along
orthogonal axes obeys Heisenberg uncertainty
principle: sxsz≥/2; sysz≥/2; sxsy≥/2
• State of definite spin in x-direction -->
50/50 superposition of up and down in z-direction.
How do we know? Stern-Gerlach Experiment
Put atoms in inhomogeneous magnetic field pointing in
z direction – split in two groups – spin up and spin down
z
What if I take just atoms that went up, and send them
through another, identical magnetic field – What happens?
z
a. Half go up (+z), half go down (–z)
b. All go up (+z)
c. All go down (–z)
d. Range of paths all smeared out
Second Experiment: What if I take just atoms that went up, and
send them through a magnetic field pointed in the x direction
– perpendicular to first field (pointing into the screen)?
z
x
a. Half go into the screen (+x), half go out of the screen (–x)
b. All go into the screen (+x)
c. All go straight (no deflection)
d. Range of paths all smeared out
e. All go up (+z)
Third Experiment: Take just the atoms that went in +x direction in
second experiment, and send them through a third magnetic field,
pointed in the z direction?
z
x
z
a. Half go up (+z), half go down (–z).
b. All go up (+z)
c. All go down (–z)
d. Range of paths all smeared out.