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1
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Periodic Table
John F. C. Turner
Department of Chemistry and
Neutron Sciences Consortium
The University of TennesseeKnoxville
2
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Structure
1. Misconceptions about the Periodic Table
2. The definition of the Periodic Table
3. Aspects of the periodicity of the elements
4. Summary
5. Questions
3
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Misconceptions
It is hard
It has no rule
It is unstructured
It is a barrier that can only be overcome by the brilliant or the odd
4
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Definition of the Periodic Table
An array of the elements in increasing atomic number or atomic mass, grouped according to chemical property
5
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Beginnings of the Periodic Table
In antiquity, prior to ~1800 only 15 – 20 elements were known;
By 1860, ~60 were isolated – enough for trends to be apparent
6
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Beginnings of the Periodic Table
Most importantly, different members of the same chemical family were isolated – the groups.
Li, Na, K,
Be, Mg, Ca, Sr,
showing similar but not identical properties
7
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
1. The majority of the elements are metals. A metal is defined as
a material whose electrical conductivitydecreases with temperature
This is obscure and is determined by the manner in which the electrons are bound in the substance
This leads to other properties that are more intuitively obvious
8
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
Non-metals and metals
9
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical propertiesMetals are
� Good conductors of heat and electricity� Malleable and ductile� Highly reflective� Opaque to visible light� Chemistry is dominated by the formation of
cations – loss of electrons
10
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
Non-metals are � Poor conductors of heat and electricity� Brittle� Chemistry is dominated by the formation of
anions – gain of electrons
11
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
Solids, liquids and gases
Strong correlation between Metals Solids
Non-metals Gases
12
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
These are bulk properties and do not explain the chemical periodicity and therefore the periodicity of the table
13
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Observed Periodicity in the physical properties
Melting points
Boiling points
Liquid range
14
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Observed Periodicity in the physical properties
The forces between particles are roughly the same in both the liquid and the solid
Periodicity in seen in the melting point, the boiling point and the liquid range
This phenomenon is independent of the phase of matter we are discussing
It is more fundamentalIt is atomic
15
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodic physical properties
However, the bulk properties and the microscopic properties must be related.
What are the trends in the ionization energy?
A � e- � A + ionization energy
16
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Periodicity of the ionization energyAcross the row, it becomes increasingly difficult to remove an electron(chemical energy scale: ~0 - ~10 eV)
Electrons are more tightly bound and therefore the atom is smaller across the table
17
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The structure of the atom and the Periodic Table
Problems with the atom:
It is a quantum system.
What is a quantum system?
One that is small on an absolute scale
What is “small on an absolute scale”
That is a good question.............
18
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The structure of the atom and the Periodic Table
“Newtonian world”
We live in a material, macroscopic world, where all energies are allowed and everything moves in a trajectory
19
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The structure of the atom and the Periodic Table
“Quantum world”
Objects are profoundly affected by the physics of observation.
No trajectories No positions No velocity
A large object is one that is perceptibly unaffected by measurement
A small object is one that is affected by measurement
20
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The structure of the atom and the Periodic Table
The atom is a quantum system.
De Broglie relationship relates themotion of a particle to wave-like properties and the electron in an atom behaves as a wave.
Standing waves have fixed energies
violin stringsorgan pipeselectrons in atoms
21
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The atom is spherical and there are three important coordinates
The distance between the electron and the nucleus
The 'longitude'
The 'latitude'
The electron-wave is defined by all three coordinates.
Each coordinate of the electron-wave has a label attached to it – the quantum number.
22
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The gross energy of the atom is dominated by the radial quantum number, n.The larger n, the larger the atom
large n
small n
n
n corresponds to the period number in the table
23
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Within each n value, there are two other labels – the longitude and the latitude
These are associated with angular motion – the circulation of the electron around the nucleus.
These quantum numbers apply to the number of groups – the s block, the p block, the d block and the f block.
s block
n
p block
d block
f block
24
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The angular quantum number, l, gives
Block l value s 0 p 1 d 2 f 3The circulation of the electron in the s block
is the smallest, 1 unit, larger in the p and so on.
s block
n
p block
d block
f block
25
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Angular momentum and the Periodic table
The angular momenta associated with the latitude and the longitude are linked.
For any value of l there are (2l+1) values of ml
Thus:
l ml
s block 0 1p block 1 3d block 2 5f block 3 7
and so on.
The ml
value can be interpreted as the
orientation of the longitudinal circulation in space.
26
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Angular momentum and the Periodic table
Givenl m
l
s block 0 1p block 1 3d block 2 5f block 3 7
We should expect 1 electron in each of the m
l quantum numbers and therefore
1 s block element per period3 p block elements per period5 d block elements per period7 f block elements per period
Instead, there are 2, 6, 10 and 14 elements?
27
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The rules of angular momentum
The final part of the structure of the Periodic Table is determined by the rules of angular momentum
'The rules of angular momentum' describe a whole range of different behaviors; they are difficult to present as their basis is very abstract.
However, they cover the properties of any body in motion and so are extremely important.
28
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The rules of angular momentum
The generalities of angular momentum are classically derived from the vector cross product together with the applications of the theory of symmetry.
Quantum mechanical angular momentum obeys the same type of rules, but translated into the quantum world.
The quantum rules are:
For every value of the angular momentum l,quantum number, thereare 2l+1 orientations, with m
l = -l....0....l
in single unit steps.
29
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The electron possesses an intrinsic angular momentum, s= ½ and therefore the two possible orientations are labeled as
ms = + ½ or - ½
The quantum labels for any electron are
Principle Angular Electron
radius, r Longitude Latitude spin
n l ml s
then four quantum numbers define the behavior of the electron in the atom.
3 space �nl
ml� 1 spin � s �
30
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Each electron in an atom is unique and its behavior is defined by the four quantum numbers.
All four must be different and therefore for each set of spatial quantum numbers, {n, l, m
l}, we
have the choice of ms = + ½ or - ½
- two choices per {n, l, ml} set.
The numbers of the elements that are available are therefore:
l ml
ms
s block 0 1 2p block 1 3 6d block 2 5 10f block 3 7 14
as required.
31
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Periodic table and the atom
The structure of the periodic table is determined in a gross manner by the atomic properties of the atoms
The precise details are not as quantitative as the description of the overall structure for several reasons.
� Electrons interact with the nucleus as well as with other electrons – an example of a many body problem
� These interactions are increasingly important as the atom becomes larger
Several trends can be identified.
32
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
The Periodic table and the atom
As the atom becomes larger, the electrons become less strongly bound.
Stronger bonds are formed between smaller atoms.
Atomic size
increases down the group for a given group
decreases across the period with increasing atomic number
33
THE UNIVERSITY OF TENNESSEE
KNOXVILLE
KNOX COUNTY SCHOOLS 13TH FEBRUARY 2004
Summary
Periodicity is seen in the Periodic Table whenever a property is based on an atomic property of some description
It is a powerful tool with which to introduce concepts important in the description of the atomic nature of the microscopic world
It is not immensely complex, but is more easily understood through the fundamental concepts that produce the structure, rather than starting with the structure.
Acknowledgments
Dr. Lynn ChampionDr. Charmaine Mamantov