1. History of the Periodic Table
Chapter 5-1
History of the Periodic Table

2. 1860
There was no method for accurately determining an element’s atomic mass or the number of atoms of an element in a particular compound.
Stanislao Cannizzaro presented a method to measure the relative masses of atoms. Also initiated the development of the periodic table.

3. Mendeleev and Chemical Periodicity
Organized element according to their chemical and physical properties.
periodic-repeating pattern
First periodic table published in 1869
Left spaces in first periodic table for undiscovered elements
Two questions:
#1: Why could most of the elements be arranged in the order of increasing atomic mass, but a few could not?
#2: What was the reason for chemical periodicity?

4. Moseley and the Periodic Law
In 1911 Henry Moseley arranged elements according to the number of protons, or atomic number.
THE PERIODIC LAW-the physical and chemical properties of the elements are periodic functions of their atomic numbers.
i.e. elements with similar properties appear at regular intervals

5. The Modern Periodic Table
The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column or group.

6. Noble Gases
In 1775 the English scientist Henry Cavendish analyzed a sample of air. He found that after all the substances then known to be in air were accounted for, a tiny part of the original sample remained.
Using two different methods to remove all known gases from air, Sir William Ramsay and Lord Rayleigh were able to announce in 1894 that they had found a monatomic, chemically inert gaseous element that constituted nearly 1 percent of the atmosphere; they named it argon.
The following year, Ramsay liberated another inert gas which proved to be helium. (Helium had previously been discovered and was known to be a component of the sun but this was the first time it was shown to exist on Earth.)

7. The Lanthanides
Early 1900’s the lanthanides are placed on the periodic table.
Atomic numbers 58 (cerium)-71 (lutetium).
New name –lanthanoids because the suffix "-ide" generally indicates negative ions.

8. Home fun
Pg 127 q 1-4

9. s block - Group 1 - Alkali Metals
Main group elements
Silvery, soft and highly reactive.
Not found in nature as free elements but found in compounds instead.
React strongly with water to produce hydrogen gas (H2) and aqueous solutions of alkalis.
Low melting point. Melting point lowers as we move down the group.

10. s-block group 2 Alkaline-earth metals
Harder, denser and stronger than alkali metals
Higher melting points than alkali metals
Still highly reactive, not found in nature…but less reactive than group 1 metals

11. Hydrogen and Helium
Placed above the Group 1 elements in the periodic table
Hydrogen’s properties do not resemble those of the other group 1 elements
Helium is placed in group 18 because with 2 electrons, its highest energy level is full
It is a noble gas…unreactive, inert.

12. d block: groups 3-12 Transition metals
Good conductors of electricity and have a high luster
Less reactive than groups 1 and 2
Some do not easily form compounds
Elements in these groups do NOT necessarily have the same outer electron configurations.

13. p-block Groups 13-18 Main group elements
Noble gases: group 18, nonreactive gases
Halogens: group 17, highly reactive gases
Metalloids: semi-conductors, brittle solids with properties of metals and nonmetals
Metals: harder/denser than s-block metals, but softer than d-block metals, sufficiently reactive

14. f-block Elements: Lanthanides and Actinides
Lanthanoids and actinoids—name change
Lanthanides: atomic numbers 58-71, shiny metals w/ reactivity similar to that of group 2
Actinides: atomic numbers , radioactive elements. First four have been found naturally occurring on Earth but all the rest are man made.