5.1 Organizing the Elements
In a video store, movies
are in categories such as
Action or Comedy. When
scientists organized the
elements, they had to
decide what categories to
use and where to place
each element. An
organized table of the
elements is one of the
most useful tools in
chemistry.
5.1 Organizing the Elements
The Search for Order
Until 1750, scientists had identified only 17
elements, mainly metals, such as copper and
iron. As the number of known elements grew,
so did the need to organize them into groups
based on their properties.
In 1789, Antoine Lavoisier grouped the known
elements into categories he called metals,
nonmetals, gases, and earths. For the next 80
years, scientists looked for different ways to
classify the elements. But no system worked
for all the known elements.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
How did Mendeleev organize the elements in
his periodic table?
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev arranged the elements into rows
in order of increasing mass so that elements
with similar properties were in the same
column.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev’s Proposal
In the 1860s, Dmitri
Mendeleev developed an
approach for organizing
the elements while playing
the card game solitaire. In
this game, the player sorts
a deck of cards
by suit and value.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev made a “deck of cards” of the elements, listing an element’s
name, mass, and properties on each card. When Mendeleev lined up the
cards in order of increasing mass, a pattern emerged. The key was to break
the elements into rows.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
The final arrangement was similar to a winning
arrangement in solitaire, except that the
columns were organized by properties instead
of suits. Within a column, the masses
increased from top to bottom.
Mendeleev’s chart was a periodic table. A
periodic table is an arrangement of elements
in columns, based on a set of properties that
repeat from row to row.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev’s Prediction
At the time Mendeleev made his table, many
elements had not yet been discovered. When
he placed the elements where their properties
fit, there were several gaps in the table.
Mendeleev was able to offer the best
explanation for how the properties of an
element were related to its location in his
table.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev was confident that the gaps in his
table would be filled by new elements. He used
the properties of elements located near the
blank spaces in his table to predict properties
for undiscovered elements.
Some scientists didn’t accept those
predictions. Others used the predictions to
help in their search for undiscovered elements.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Evidence Supporting Mendeleev’s Table
What evidence helped verify the usefulness
of Mendeleev’s table?
5.1 Organizing the Elements
Mendeleev’s Periodic Table
The close match between Mendeleev’s
predictions and the actual properties of new
elements showed how useful his periodic
table could be.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Mendeleev named missing elements after
elements in the same group. He gave the
name eka-aluminum to the missing element
one space below aluminum in the table.
Mendeleev predicted that eka-aluminum would
• be a soft metal,
• have a low melting point, and
• have a density of 5.9 g/cm3.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
In 1875, a French chemist discovered a new
element. He named the element gallium (Ga)
in honor of France. (The Latin name for France
is Gallia.) Gallium
• is a soft metal,
• has a melting point of 29.7°C, and
• has a density of 5.91 g/cm3.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Heat from a person's hand can melt gallium.
In some traffic signals, there are tiny light
emitting diodes (LEDs) that contain a
compound of gallium.
5.1 Organizing the Elements
Mendeleev’s Periodic Table
Scientists use the periodic table to explain the
chemical behavior of different groups of
elements.
• The properties of gallium are remarkably similar
to the predicted properties of eka-aluminum.
Scientists concluded that gallium and ekaaluminum are the same element.
• The discovery of scandium (Sc) in 1879 and the
discovery of germanium (Ge) in 1886 provided
more evidence.
5.1 Organizing the Elements
Assessment Questions
1. In Mendeleev’s periodic table, elements with
similar properties were grouped
a. in the same row.
b. in the same column.
c. in diagonal lines that run from top left to the bottom
right.
d. in pairs of two.
5.1 Organizing the Elements
Assessment Questions
1. In Mendeleev’s periodic table, elements with
similar properties were grouped
a. in the same row.
b. in the same column.
c. in diagonal lines that run from top left to the bottom
right.
d. in pairs of two.
ANS: B
5.1 Organizing the Elements
Assessment Questions
2. For which element did Mendeleev correctly predict
the properties even before it had been
discovered?
a.
b.
c.
d.
gallium
hydrogen
bromine
aluminum
5.1 Organizing the Elements
Assessment Questions
2. For which element did Mendeleev correctly predict
the properties even before it had been
discovered?
a.
b.
c.
d.
gallium
hydrogen
bromine
aluminum
ANS:
A