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Unit 1 : Periodicity of Elements

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Ahmed Hussein

on 23 August 2016

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Transcript of Unit 1 : Periodicity of Elements

1-He left gaps in his table for elements not found in his time & predicted the discovery of new elements & predicted their properties & their atomic weights.

2-He corrected the atomic weights of some elements which were estimated wrongly.

Advantages of Mendeleev’s table
Many
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.
Classification
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
isotopes
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
Mr.Ahmed Elbasha
Thank You
Unit 1 : Periodicity of Elements and their Properties
Lesson 1 : Attempts of elements classification
Mr.Ahmred Elbasha

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.
2016/2017
How ?!
Mendeleev
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
groups
. The horizontal rows in the table are known as
periods
.
The properties of elements were repeated periodically by the beginning of each new
period
.
Modification
: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,

and
he added the inert gases in the (0) zero group,

and
he located a place below his periodic table for the two groups
lanthanides
and
actinides
.
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
period
.

There’re
7 periods
in the periodic table.

The physical & chemical properties of elements in a period change gradually from left to right.

Each
vertical
column of elements is called a group.

There’re 18 columns in the periodic table.

Elements in a group have similar properties.

s-block elements
d-block elements
p-block elements
f-block elements
s-block elements

-They are found on the left side of the periodic table.
-They are 2 groups (1A) and (2A).

d-block elements
-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)

p-block elements
-They are found on the right side of the periodic table.
-They are 6 groups (3A),(4A),(5A),(6A)
(7A) and zero
f-block elements
-are located below the periodic table
-include lanthanides and actinides

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