Chapter 5
The Periodic Law
Modern Russian Table
Chinese Periodic Table
Orbital Filling Table
Periodic Table with Group Names
Chapter 5
The Periodic Law
5.1 History of the Periodic Table
Predecessors to the Modern Periodic
Table
• Dobereiner’s Triads
J.W. Dobereiner classified some elements
into groups of three, which he called
triads.
• similar chemical properties
• physical properties varied in an orderly
way according to their atomic masses.
Mendeleev’s Periodic Table
Dmitri Mendeleev
Predecessors to the Modern Periodic
Table
• Mendeleev’s Periodic Table
Dmitri Mendeleev realized that the chemical and
physical properties of the elements repeated in an
orderly way when he organized the elements
according to increasing atomic mass.
• In 1869, Mendeleev published a table of the elements
organized by increasing atomic mass.
• Mendeleev was a Russian scientist and is often
referred to as the “Father” of the Periodic Table.
• Periodicity is the tendency to recur at regular
intervals.
Mendeleev’s Table
"The chemical properties of the elements are a periodic function of
their atomic weights"
Mendeleev's Periodic Table
Horizontal rows have similar
chemical properties
Vertical
column
s in
atomic
weight
order
• Mendeleev made some exceptions to
place elements in rows with similar
properties (tellurium & iodine's places were switched)
• Missing Elements: gaps existed in Mendeleev’s table
• Mendeleev predicted the properties of the “yet to be
discovered” elements
(scandium, germanium and gallium)
Problems with Mendeleev’s Table
Why didn't some
elements fit in order of
increasing atomic
mass?
Why did elements exhibit
periodic behavior?
Moseley helped to clarify some of the problems…
Henry Moseley 1887-1915
• English physicist who determined
the number of positive charges in
the nucleus (protons) by measuring
the wavelength of the x-rays given
off by certain metals in 1913.
• He was killed by a sniper in Turkey
in August 1915 during WWI. Many
people think that Britain lost a future
Nobel Prize winner. This is because
Nobel Prizes, the most prestigious
awards for scientific achievement
are awarded only to living people.
Moseley and the Periodic Table
• Protons and Atomic Number:
X-ray experiments revealed a way to determine the
number of protons in the nucleus of an atom
The periodic table was found to be in atomic
number order, not atomic mass order!!!
• This explained tellurium-iodine anomaly
The Periodic Law
The physical and chemical properties of the
elements are periodic functions of their atomic
numbers
• ***Moseley was killed in battle in 1915, during WWI.
He was 28 years old
Discovery of the Noble Gases
Helium
discovered as a
component of
the sun, based
on the emission
spectrum of
sunlight
1868
William
Ramsay
discovers
argon
Ramsay
finds helium
on Earth
Ramsay
discovers
krypton
and xenon
Freidrich
Dorn
discovers
radon
1894 1895 1898
1900
Sir William Ramsay
• The Lanthanides
Early 1900's the elements from cerium (#58) to
lutetium (#71) are separated and identified. Also
known as the rare earth elements, less than 0.01%
naturally occurring.
• The Actinides
Discovery (or synthesis) of thorium, # 90 to
lawrencium #103
• Both groups pulled out of the table for space reasons.
• Periodicity:
Elements with similar properties are found at regular
intervals within the "periodic" table
Chapter 5
The Periodic Law
5.2 Electron Configuration &
The Periodic Table
1 2
3 4 5
6 7
8 9 10 11 12 13 14 15 16 17 18
Sublevel Blocks on
the Periodic Table
The Properties of a Group:
the Alkali Metals
Easily lose 1 valence electron
(Reducing agents)
React violently with water
React with halogens to form salts
The Properties of a Group:
the Alkali Earth Metals
Easily loses 2 valence electron
(Reducing agents)
Harder, denser, stronger than
Group 1 metals
Higher melting points
Less reactive than Group 1, but too
reactive to be found free in nature
Chapter 5
The Periodic Law
5.3 Electron Configuration &
Periodic Properties
Determination of Atomic Radius:
Half of the distance between nuclei in
covalently bonded diatomic molecule
"covalent atomic radii"
Periodic Trends in Atomic Radius:
Radius decreases across a period
Increased effective nuclear charge due
to decreased shielding
Radius increases down a group
Addition of principal quantum levels
Table of
Atomic
Radii
How to Achieve an Octet…
• Atoms can form ions by gaining or losing
electrons to obtain a stable outer configuration
• Cation- Positive ion (+) ion
• Anion- Negative ion (-) ion
• Ions attract (opposites attract)
Predicting Ionization
• Metals tend to lose electrons
They form cations.
Ex: Na, 1s22s22p63s1 becomes Na+1,1s22s22p6
• Nonmetals tend to gain electrons.
They form anions.
Ex: O, 1s22s22p4 becomes O-2, 1s22s22p6
Electron Transfer: Anions
• When an atom gains electrons it increases its
negative charge so it becomes negatively
charged. There are now more electrons than
protons.
X + e- = X –
Ex: Nitrogen Atom
+ 7 protons
- 7 electrons
Nitrogen Ion
+7 protons
- 10 electrons
Neutral
-3
charge
Electron Transfer: Cations
• When an atom loses electrons, it loses negative
charges so it becomes more positively charged.
There are now more protons than electrons.
X - (e-) = X +
Ex: Potassium Atom
Potassium Ion
+ 19 protons
- 19 electrons
+19 protons
-18 electrons
Neutral
+1
charge
Ionization Energy - the energy required to remove
an electron from an atom
Increases for successive electrons taken from
the same atom
Tends to increase across a period
Electrons in the same quantum level do not
shield as effectively as electrons in inner
levels
Irregularities at half filled and filled sublevels
due to extra repulsion of electrons paired in
orbitals, making them easier to remove
Tends to decrease down a group
Outer electrons are farther from the nucleus
Ionization of Magnesium
Mg + 738 kJ  Mg+ + eMg+ + 1451 kJ  Mg2+ + eMg2+ + 7733 kJ  Mg3+ + e-
Table of 1st Ionization Energies
Another Way to Look at Ionization
Energy
Electron Affinity - the energy change associated
with the addition of an electron
Affinity tends to increase across a period
Affinity tends to decrease down a group
Electrons farther from the nucleus
experience less nuclear attraction
Some irregularities due to repulsive
forces in the relatively small p orbitals
Table of Electron Affinities
Ionic Radii
Cations
Positively charged ions
Smaller than the corresponding
atom
Anions
Negatively charged ions
Larger than the corresponding
atom
Summation of Periodic Trends
Table of Ion Sizes
Electronegativity
A measure of the ability of an atom in a chemical
compound to attract electrons
Electronegativities tend to increase across
a period
Electronegativities tend to decrease down a
group or remain the same
Periodic Table of Electronegativities