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Unit 1 : Periodicity of Elements
Transcript of Unit 1 : Periodicity of Elements
2-He corrected the atomic weights of some elements which were estimated wrongly.
Advantages of Mendeleev’s table
attempts are made by scientists for classification of elements to be easily studied,
and find the relation between elements and their physical and chemical properties.
the first real periodic table for classification of the elements.
67 Element were Known
Mendeleev's periodic table
1. He Had to make a disturbance in the ascending order of atomic weight of some elements to put them in groups that suit their properties
2. considered the
as different elements
disadvantages of Mendeleev’s table
In 1913, the Newzealand Scientist Rutherford discovered that the nucleus of atom contains positively charged protons, the British Scientist Moseley discovered in the same year
after studying the properties of x rays that the periodicity of elements properties is related to
their atomic number not their atomic weights as Mendeleev believed.
Moseley’s periodic table
Unit 1 : Periodicity of Elements and their Properties
Lesson 1 : Attempts of elements classification
After the Danish Scientist Bohr discovered the main energy levels . as shown
The modern periodic table
Elements were classified in the modern periodic table according to their ascending atomic numbers & according to the filling of energy sublevels with electrons.
was a Russian chemist who arranged elements in a table in order of increasing atomic weights.
He found that elements properties followed a pattern that repeated every 7 elements & therefore he arranged elements of similar properties in vertical columns known as
. The horizontal rows in the table are known as
The properties of elements were repeated periodically by the beginning of each new
:So Moseley rearranged the elements in an ascending order according to their atomic number such that the atomic number of an element increases by one than the element before it in the same period,
he added the inert gases in the (0) zero group,
he located a place below his periodic table for the two groups
Scientists discovered that electrons are found in energy levels around the nucleus. The heaviest atom contains 7 energy levels.
Each main level contains regions where electrons can exist according to their energy, these were called energy sublevels .
Each horizontal row of elements is called a
in the periodic table.
The physical & chemical properties of elements in a period change gradually from left to right.
column of elements is called a group.
There’re 18 columns in the periodic table.
Elements in a group have similar properties.
-They are found on the left side of the periodic table.
-They are 2 groups (1A) and (2A).
-They are found in the middle of the periodic table.
-They are arranged in 8 groups (3B),(4B),(5B),(6B),(7B),(8),(1B) and (2B).
-They are known as transitional elements
-They start appearing in period (4)
-They are found on the right side of the periodic table.
-They are 6 groups (3A),(4A),(5A),(6A)
(7A) and zero
-are located below the periodic table
-include lanthanides and actinides
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