Periodic table history and Family of periodic table

 Periodic table history


-A necessary prerequisite to the construction of
the periodic table was the discovery of the individual elements.
-By 1869, a total of 63 elements had been discovered.

--------------------------------------------

-Between 1863 and 1866 John Newlands
 showed that by assigning Hydrogen an
 arbitrary mass of 1 and ordering the known
 elements by their masses, every eighth
 element shared a common set of properties
-He called this the “law of octaves
----------------------------------------------
-1869, Dimitri Mendeleev published a method of

 organizing the elements according to both
 their masses and their properties.
 -Mendeleev showed that when the elements
 are listed according to masses, certain
 properties recur PERIODICALLY.
- He broke the list into a series of rows
(PERIOD) and columns (GROUP).

-----------------------------------------------


l He placed elements in certain groups based on
their properties in spite of contrary indications by its
mass
 Mendeleev left gaps in his table for elements, which
he proposed had yet to be discovered.
 He was able to predict the properties and
characteristics of the undiscovered elements so
accurately that when they were discovered the
predicted value was quite exact.
 The periodic table allowed chemists to organize
and understand their data and predict new






----------------MODERN PERIODIC TABLE-----------------------------



Is organized according to atomic number rather than
atomic mass. (This solved the problems where
different isotopic abundances caused the masses to
be “out of order”. Example: Ar and K, Co and Ni)
The periodic law summarizes the periodic table.
l The Periodic Law: Properties of the chemical elements
recur periodically when the elements are arranged from
lowest to highest atomic numbers
Major Divisions in the Periodic Table
l Period: The set of all elements in a given row going
across the table.
l Group or Family: The set of all elements in a given
column going down the table.

-------------------------------------------------------
THE Family of Periodic table


----Alkali Metal = elements in the first column (Except H)
----Alkaline Earth Metals = The elements in the second column
----Halogens = second column from the end on the right hand side. Starting with Fluorine.
----Noble Gases = Far right side of the table. Starting with helium.
----Lanthanide = elements in the first row shown underneath the table. Starting with lanthanum.
----Actinides = underneath the Lanthanides. Starting with actinium.

..................................................
Metals, Nonmetals, Semiconductors

Metal: reflect light when polished
       are opaque
       are good conductors of electricity and heat
       are malleable or rolled into thin sheets and ductile
       are usually solid at room temperatures
..........................................................

Non metals

Non metal: liquids or brittle solids at room temperature
           Poor conductors of heat and electricity
           Solids are dull to lustrous in appearance and opaque to translucent
           Non – Metals can be divided into two subgroups:
                  1.Very low electrical conductivities
                  2.Fair to moderate conductivities

.........................................................

Semiconductor
    A non-metal having an electrical conductivity, which increases with teperature.
    Semiconductors (Metalloids or Semimetals) have properties which resemble metals more than nonmetals
    Important difference is that metal conductivity
    decreases with increasing temperature whereas the electrical conductivity of semiconductors
     increases with increasing temperature.
0.................................................