Periodicity
Chapter 5
Element song (Tom Lehrer),
http://www.privatehand.com/flash/elements.html
with Daniel Radcliffe:
http://www.youtube.com/watch?v=rSAaiYKF0cs
New element song:
http://www.nclark.net/Meet_the_Elements.html
Other good websites for the periodic table:
http://periodic.lanl.gov
http://www.periodicspiral.com/
www.wou.edu/las/physci/ch412/perhist.htm
www.chemsoc.org/viselements/pages/history.html
http://www.chemeddl.org/resources/ptl/
http://www.ptable.com/
The History of the Development of
the Periodic Table
In the 1790’s Antoine Lavoisier (French Chemist)
compiled a list of 23 elements. Some of these were
gold, silver, carbon, oxygen.
In 1860 Stanislao Cannizzaro (Italian chemist)
presented a method for accurately measuring the
relative masses of atoms.
In 1864 John Newlands(English Chemist) noticed
that when elements were arranged by increasing
atomic mass, their properties repeated every
eighth element. He called this the Law of Octaves
Lothar Meyer and Dimitri Mendeleleev
In 1869 Lothar Meyer (German chemist) and Dmitri
Mendeleev (Russian chemist) each demonstrated a
connection between atomic mass and elemental
properties.
However, Mendeleev produced the first useful and
widely accepted periodic table arranged in order of
increasing atomic mass.
An important facet of his table was that he left blank
spaces in the table where he thought undiscovered
elements should go.
Mendeleev is considered the “father” of the periodic
table.
Henry Moseley
In 1913 Henry Moseley(English chemist) discovered
that atoms of each element contain a unique
number of protons in their nuclei—the number of
protons being equal to the atom’s atomic number.
He proposed the Periodic Law, which states that
there is a periodic repetition of chemical and
physical properties of the elements when they are
arranged by increasing atomic number.
His arrangement of elements by atomic number
resulted in a clear periodic pattern of properties.
This is the basis of the Modern Periodic Table which
we are using now.
Properties of some elements predicted by Mendeleev
Predicted
elements
Element &
year
discovered
Properties
Predicted
properties
Observed
properties
Ekaaluminum
Gallium
1875
Density of metal
6.0 g/ml
5.96 g/ml
Melting point
Low
30 °C
Oxide formula
Ea2O3
Ga2O3
Density of metal
3.5 g/ml
3.86 g/ml
Oxide formula
Eb2O3
Sb2O3
Solubility of oxide
Dissolves in
acid
Dissolves in acid
Melting point
High
900°C
Density of metal
5.5 g/ml
5.47 g/ml
Color metal
Dark gray
Grayish white
Oxide formula
EsO2
GeO2
Density of oxide
4.7 g/ml
4.70 g/ml
Chloride formula
EsCl4
GeCl4
Ekaboron
Ekasilicon
Scandium
1877
Germanium
1886
Periodic
Law: The physical and
chemical properties of the elements
are periodic functions of their atomic
numbers. This periodicity in properties
of the elements is a function of the
arrangement of electrons around the
nucleus of an atom (remember that
the # of electrons = the # of protons
in a neutral atom)
 Valence electrons: The electrons
available to be lost, gained, or
shared in the formation of chemical
compounds; i.e. the “outer shell”
electrons.
Periodic trends
Atomic radii: one
half the distance
between the
nuclei of identical
atoms that are
bonded together.
Atomic radii vs. atomic number
Atomic Radii vs. atomic number
Cations
Anions
Ionization energy
The energy required to remove
one electron from a neutral
atom or an element. (kJ/mol)
A + energy 
+
A
+
e
Electron Affinity
The energy change that occurs when an electron is
acquired by a neutral atom.
Most atoms RELEASE energy when they acquire an
electron.
A + e-  A- + energy
Some atoms must be “forced” to gain an electron by
the addition of energy.
A + e- + energy  A-
Electron affinity vs. atomic number
Electronegativity
a measure of the ability of
an atom in a chemical
compound to attract
electrons. Highest value is
arbitrarily given to
Fluorine of 4.0.
Electronegativity
General reactivity trends