Periodic Table

1. Periodic Table The how and why

2. History • 1829 German J. W. Dobereiner Grouped elements into triads • Three elements with similar properties • Properties followed a pattern • The same element was in the middle of all trends • Example: Ca, Ba, Sr • Not all elements had triads

3. 1863 – John Newlands suggested another classification. • Put elements in order of increasing atomic masses. • Found repetition of similar properties every 8th element. • He arranged the elements (known at that time) into 7 groups of 7. • Law of Octaves

4. Russian scientist Dmitri Mendeleev taught chemistry in terms of properties • Wrote down the elements in order of increasing mass • Found a pattern of repeating properties • Difference – thought that similar properties occurred over periods (rows) of varying length.

5. Mendeleev’s Table • Grouped elements in columns by similar properties in order of increasing atomic mass • Found some inconsistencies - felt that the properties were more important than the mass, so switched order. • Found some gaps • Must be undiscovered elements • Predicted their properties before they were found

7. The Modern Table • Elements are still grouped by properties • Similar properties are in the same column • Late 1800’s added a column of elements Mendeleev didn’t know about. • 1911 - Henry Moseley recognized increasing nuclear charge was a better order for arranging elements

8. Horizontal rows are called periods • There are 7 periods

9. Vertical columns are called groups. • Elements are placed in columns by similar properties. • Also called families

10. 8A0 1A • The elements in the A groups are called the representative elements 2A 3A 4A 5A 6A 7A

11. VIIIB IA IIA VIB VIIB IIIB IVB VB 1 1A 2 2A 8A 18 13 3A 14 4A 15 5A 16 6A 7A 17 VIIIA VIA VIIA IIIA IVA VA IB IIB 3 3B 4B 4 5 5B 6B 6 7 7B 8 8B 9 8B 10 8B 1B 11 2B 12 Other Systems

12. Metals

13. Metals • Luster – shiny. • Ductile – drawn into wires. • Malleable – hammered into sheets. • Conductors of heat and electricity.

14. Transition metals • The Group B elements

15. Non-metals • Dull • Brittle • Nonconductors- insulators

16. Metalloids or Semimetals • Properties of both • Semiconductors

17. These are called the inner transition elements and they belong here

19. Group 1A are the alkali metals • Group 2A are the alkaline earth metals

20. Group 6A is called the chalcogens • Group 7A is called the Halogens • Group 8A are the noble gases

21. Alkali metals (group 1): Extremely reactive, soft metals with low density that form ions with a +1 charge. • Alkaline earth metals (group 2): Slighly less reactive than alkali metals, they are somewhat denser and less soft. They form ions with a +2 charge.

22. Halogens (group 17): Highly reactive and electronegative nonmetallic elements that form ions with a -1 charge. They are diatomic, volatile, and very difficult to handle safely. • Noble gases (group 18): Very stable nonmetallic gases that react poorly with other elements.

23. Transition metals (groups 3-12): Dense, hard metallic elements that usually form ions with more than one possible positive charge. • Lanthanides and actinides (the two rows at the bottom of the periodic table): The lanthanides are the top row and are reactive, dense metals. The actinides are the bottom row and include mainly radioactive elements that are produced artificially.

24. Main group elements: These elements consist of groups 1, 2, and 13-18.