1. 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.

2. 5.1 Organizing the Elements 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. The Search for Order

3. 5.1 Organizing the Elements 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.

4. 5.1 Organizing the Elements How did the Russian chemist Dmitri Mendeleev organize the elements in his periodic table? Mendeleev’s Periodic Table

5. 5.1 Organizing the Elements 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. Mendeleev’s Periodic Table

6. 5.1 Organizing the Elements Mendeleev 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 Notes

7. 5.1 Organizing the Elements 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. Mendeleev’s Periodic Table

8. 5.1 Organizing the Elements 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. Mendeleev’s Periodic Table

9. 5.1 Organizing the Elements Mendeleev’s Prediction At the time Mendeleev made his table, - Only 63 elements known - many elements were not discovered - placed elements on table, left several gaps Mendeleev’s Periodic Table Notes

10. 5.1 Organizing the Elements Notes Period -r-regular, repeating pattern -c-class, hockey, library, sentence -A-A periodic table is an arrangement of elements in columns, based on a set of properties that repeat from row to row.

11. 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. Mendeleev’s Periodic Table

12. 5.1 Organizing the Elements What evidence helped verify the usefulness of Mendeleev’s table? Evidence Supporting Mendeleev’s Table Mendeleev’s Periodic Table

13. 5.1 Organizing the Elements The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be. Mendeleev’s Periodic Table

14. 5.1 Organizing the Elements 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 (eka means “next in order of group) be a soft metal, have a low melting point, and have a density of 5.9 g/cm 3. Mendeleev’s Periodic Table

15. 5.1 Organizing the Elements 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 (85.7 ºF), and has a density of 5.91 g/cm 3. Mendeleev’s Periodic Table

16. 5.1 Organizing the Elements 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. Mendeleev’s Periodic Table

17. 5.1 Organizing the Elements 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 eka- aluminum are the same element. The discovery of scandium (Sc) in 1879 and the discovery of germanium (Ge) in 1886 provided more evidence. Mendeleev’s Periodic Table

18. 5.1 Organizing the Elements The Periodic Table

19. 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.

20. 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

21. 5.1 Organizing the Elements Assessment Questions 2.For which element did Mendeleev correctly predict the properties even before it had been discovered? a.gallium b.hydrogen c.bromine d.aluminum

22. 5.1 Organizing the Elements Assessment Questions 2.For which element did Mendeleev correctly predict the properties even before it had been discovered? a.gallium b.hydrogen c.bromine d.aluminum ANS:A