1. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

2. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

3. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

4. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

5. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

6. 5-1 The Search for order Why did they begin to organize the elements?
How did they start the organization?
Mendeleev's Periodic Table.
Mendeleev’s Proposal
How did he arrange it?
What made him come up with the arrangement?
Mendeleev’s Prediction
Evidence Supporting Mendeleev’s table

7. Periodic songs and videos
Tom Lehrer-Lobachevshy
They Might Be Giants
Harry Potter

8. In a video store, movies are in categories such as Action or Comedy
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.

9. Organizing the Elements
The Search for Order
Until 1750, scientists had identified only 17 elements, mainly metals, such as copper and iron.
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.

10. 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.

11. 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.

12. Mendeleev’s Proposal
Elements in columns were organized by properties
Within a column, the elements masses increased from top to bottom
His chart was a periodic table- an arrangement of elements in columns, based on a set of properties that repeat from row to row.
A calendar is another example of a periodic table

13. Mendeleev’s Prediction
Mendeleev was able to offer the best explanation for how the properties of an element were related to its location in his table.
When he placed the elements where their properties fit, there were several gaps in the table.
He used the properties of elements located near the blank spaces in his table to predict properties for undiscovered elements.

14. Mendeleev’s Periodic Table
Mendeleev was confident that the gaps in his table would be filled by new elements.
Some scientists didn’t accept those predictions. Others used the predictions to help in their search for undiscovered elements.

15. 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 named a missing element one space below aluminum eka-aluminum
He predicted the properties to be
A soft metal
Low melting point
Density about 5.9 g/cm3

16. In 1875, a French chemist discovered a new element and named it gallium (Ga) in honor of France.
The properties were:
is a soft metal,
has a melting point of 29.7°C, and
has a density of 5.91 g/cm3.

17. 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.

18. Scientists use the periodic table to explain the chemical behavior of different groups of elements.
The discovery of scandium (Sc) in 1879 and the discovery of germanium (Ge) in 1886 provided more evidence.

19. Assessment Questions
In Mendeleev’s periodic table, elements with similar properties were grouped
in the same row.
in the same column.
in diagonal lines that run from top left to the bottom right.
in pairs of two.

20. Assessment Questions
In Mendeleev’s periodic table, elements with similar properties were grouped
in the same row.
in the same column.
in diagonal lines that run from top left to the bottom right.
in pairs of two. ANS: B

21. Assessment Questions
For which element did Mendeleev correctly predict the properties even before it had been discovered?
gallium
hydrogen
bromine
aluminum

22. Assessment Questions
For which element did Mendeleev correctly predict the properties even before it had been discovered?
gallium
hydrogen
bromine
aluminum
ANS: A