Mendeleev`s Periodic Table

How does a deck of cards and world
map relate to the periodic table?
Ch 5.1 – Finding Order
The Search for Order
 Until 1750  Only 17 elements had been identified
 Mainly metals - such as copper and iron.
 Alchemists
 Natural abundance
 As the number of known elements
grew, so did the need to organize and
present them in a universal manner.
The Search for Order
In 1789 - Antoine Lavoisier
Grouped the known elements into 4 categories
 Metals
 Nonmetals
 Gases
 Earths
For the next 80 years, scientists looked for
different ways to classify the elements. But no
system worked for all the known elements.
Mendeleev’s Periodic Table
Mendeleev’s Proposal
 1869 - Dmitri Mendeleev developed an approach for
organizing the elements while playing a game solitaire.
 Making observations about how the cards were sorted (by
suit and value) provided Mendeleev with an idea
Mendeleev’s Periodic Table
Mendeleev made a “deck of cards” of the
~60 known elements
 Listed on each card - an element’s
 Name
 Mass
 Properties
Mendeleev lined up the cards in order of
increasing mass
 A new pattern emerged
Mendeleev’s Periodic Table
New Pattern
The key was to break the elements into rows.
Continued creating a row based on increasing
mass until he came across an element with
properties similar to those of one already in the
Started a new row
Elements with similar properties were
organized in columns
Mendeleev’s Periodic Table
Mendeleev’s Periodic Table
How did Mendeleev organize the elements
in his periodic table?
He arranged the elements into rows in order
of increasing mass so that elements with
similar properties were in the same column.
Mendeleev’s Periodic Table
 The final arrangement was similar to a winning
arrangement in solitaire:
 Columns were organized by properties (suits)
 Within a column, the masses increased from top to bottom
Trend – Mass Increases from left to right & top to bottom
 Mendeleev’s chart became the 1st universal periodic
 A periodic table is an arrangement of elements in columns,
based on a set of properties that repeat from row to row.
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
 Confident that gaps would be filled by NEW
Mendeleev’s Periodic Table
Mendeleev’s Prediction
 He used the properties of elements located near the
gaps in his table to predict properties for
undiscovered elements.
 Able to offer the best explanation for how the properties of
an element were related to its location in his table.
 Some scientists didn’t accept those predictions.
 Others used the predictions to help in their search for
undiscovered elements.
Evidence Supporting Mendeleev’s Table
The close match between Mendeleev’s predictions and the
actual properties of new elements showed how useful his
periodic table could be.
 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
have a density of 5.9 g/cm3
Evidence Supporting Mendeleev’s
 In 1875, a French chemist discovered a new
 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
So low a persons body heat will melt it
 has a density of 5.91 g/cm3
Evidence Supporting Mendeleev’s
 The discovery of other elements and their properties
provided even further evidence to support Mendeleev’s
 Scandium (Sc) in 1879
 Germanium (Ge) in 1886
 Today scientists use the periodic table to explain the
chemical behavior of different groups of elements
Assessment Questions
1. How many elements were discovered
between1750 and the 1869?
a. ~20
b. ~40
c. ~30
d. ~60
Assessment Questions
2. Following his observations, Mendeleev
began organizing the elements by lining them
up in order of
a. Decreasing mass
b. Increasing atomic number
c. Increasing mass
d. Increasing melting point
Assessment Questions
3. 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.
Assessment Questions
4. Mendeleev made predictions regarding the
gaps in his table by
a. Using only the masses of the surrounding
known elements
b. Using the known elements subatomic
c. Using only the known elements melting points
d. Using all the various properties of the known
elements surrounding the gaps
Assessment Questions
5. For which element did Mendeleev correctly
predict the properties even before it had
been discovered?
a. gallium
b. hydrogen
c. bromine
d. aluminum