The Periodic Table
Glencoe: Chapter 19-3
Page 588-596
Organizing the Elements
• Late 1800’s (1871),
Dmitri Mendeleev
• Russian chemist
• Created 1st periodic table
by placing all known
elements (at that time ~
60 elements) in order by
increasing atomic mass
(number of neutrons +
number of protons)
Organizing the Elements
• Discovered a pattern
 Heavier elements repeated the chemical properties of lighter
elements
 Periodic properties – a repeating pattern of chemical properties
Early Periodic Tables
• This table show gaps for unknown elements
Organizing the Elements
• Mendeleev left blank spaces in his
arrangement in order to attempt to align
elements with similar properties
• Predicted chemical properties and atomic
masses of elements not yet known, for
which he had left blank spaces to be filled
in when the elements were discovered.
Organizing the Elements
• Mendeleev’s predictions were
correct
• When found, the
missing elements in
Mendeleev’s table did
possess properties and
masses very close to
Mendeleev’s predictions
• Known as the “Father of the
Periodic Table”
Improving the Periodic Table
• As more elements were discovered,
Mendeleev’s table needed some changes
to deal with inconsistencies
• 1913 – Henry Moseley
(English scientist) –
arranged the elements
by increasing atomic
number (number of protons)
Improving the Periodic Table
• This new arrangement corrected some
inconsistencies in the periodic properties
• The modern / current periodic table is
arranged by increasing atomic number,
from Moseley.
Periodic Table
Periodic Table
Table Parts
• Groups – vertical columns (up-anddown) of elements on the periodic table
• All elements in a group share / possess
similar chemical properties, and
electron arrangements
• Also called families of elements
• There are 18 groups / families of
elements
Table Parts
• Periods – horizontal rows (side-to-side) of
elements on the periodic table
• There are 7 periods
• Elements increase atomic number from left to
right across a period
Regions of the Table /
Classifications
• There are four general regions on the
periodic table.
• 1. Metals
• 2. Metalloids
• 3. Non-metals
• 4. Noble gases
Table Regions
Synthetic elements / Man-made
elements
• Scientists are continually attempting to
make new, bigger (higher atomic number),
and heavier elements
• They smash particles and atoms together
to see what “sticks”
Synthetic elements / Man-made elements
• Most break down on their own 
radioactive
• Radioactive elements / isotopes of
elements are unstable and break apart on
their own into parts that are more stable
Elements in the Universe
• Through study it appears that the universe
is made of all the same stuff
• Hydrogen (H) and Helium (He) are the
most abundant elements in the universe.
Elements in the Universe
• Heavier elements are constantly being
formed in stars by nuclear fusion (joining
of smaller nuclei into larger nuclei).