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

6. Predicted Properties - Ekasilicon
Actual Properties - Germanium
Atomic mass 72
72.6
Melting Point high
958
Density 5.5 g/cm3
5.36 g/cm3
Dark gray metal
Gray metal
Will obtain from K2EsF6
K2GeF6
Slightly dissolved by HCl
Not dissolved by HCl
Will form EsO2
Does form oxide (GeO2)
Density of EsO g/cm3
Density of GeO2 = 4.70 g/cm3

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.
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. The elements in the A groups are called the representative elements

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

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): Slightly 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.