History of The
Periodic Table
Objectives
• Explain how elements are
organized in a periodic table
• Compare early and modern
periodic tables
• Identify 3 broad classes of
elements
Important Vocabulary
• Triad
• Law of Octaves
• Periodic Law
• Group
• Period
• Malleable
• Ductile
• Metalloid
Searching for an Organizing
Principle
• By 1700, only 13 elements had been
identified
• By the decade of 1765-1775, 5 new
elements had been discovered with the
increased use of the scientific method
• However, as more elements were
discovered in the years following, a need
for a classification system became
important
J.W. Dobereiner
• In 1829, this German chemist published a
classification system
• Within his system, element were grouped into
triads
• A triad is a set of 3 elements with similar
properties
• Problem: all the known elements could not be
grouped into triads
John Newlands
• Was an English chemist
• In 1865, he arranged the known elements according
to their properties and in order of increasing
atomic mass
• In doing this he noticed that all the elements in a
given row had similar chemical and physical
properties
• It seemed that this pattern repeated every eight
elements
• He called this observed pattern the law of octaves
John Newland’s Periodic Table
Dmitri Mendeleev
• Was the inventor of the first periodic table in
1869
• He was a Russian chemist who used Newland’s
observations and other information to create a
table arrangement
• His table only had 63 elements
Creating the 1st Periodic Table
• He wrote a symbol for each element, along with the
physical and chemical properties and the relative
atomic mass of the element on cards
• He arranged the elements in order of increasing
atomic mass
• He started a new row everything he notices the
elements chemical properties repeated
• In addition, he left gaps in his table for elements he
predicted should fit there
Henry Moseley
• Was an English chemist
• In 1914, he found a different physical basis for
the arrangement of the elements
• He studied the X-ray spectra of 38 different
elements and found that the wavelengths of the
lines in the spectra decreased in a regular manner
as atomic mass increased
• He ultimately developed the concept of atomic
number
• Thus, the periodic table was arranged by atomic
number rather than atomic mass
Periodic Law
• States that when the elements are arranged
according to their atomic numbers, elements
with similar properties appear at regular
intervals
• So why does this happen?
• It has to do with the electron configurations
of elements
Organization of the Periodic
Table
• Elements in each column of the table have the
same number of electrons in their outer energy
level.
• These outer electrons are called valence
electrons
• A vertical column on the periodic table is called
a group
• Where as a horizontal row on the periodic table
is called a period
3 Main Groups of Elements
• Elements are classified into 3 main
groups
• Metals
• Nonmetals
• Metalloids (aka Semiconductors)
Metals
• There are 6 types of metals in the periodic
table
Alkali metals
Alkaline-earth metals
Transition metals
Rare Earth metals
Synthetic metals
Other metals
Characteristics of Metals
• Many elements are classified as metals
• Most of them are located in the middle of the
periodic table
• Metals are good conductions of heat & electric
current
• They are malleable and ductile
• Malleable means that they are easily formed
• Ductile means that they can be drawn into wires
• Metals also have luster
Nonmetals
• Are found throughout the periodic table
• Groups 13-16, 17 & 18 and hydrogen
• They are poor conductors of heat and
electric current
• Only exception to this rule is carbon
• Solid nonmetals tend to be brittle and will
shatter if hit with a hammer
• What elements do they include?
Semiconductors
• Are intermediate conductors of heat &
electricity
• Also known as metalloids
• Include only 7 elements: Boron, Silicon,
Germanium, Arsenic, Antimony, Tellurium
and Astatine
• Silicon is the most familiar semiconductor
• What is it used for?