The Periodic Table (الجدول الدورى مراجعة لغات)

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Introducti on Scientists tried to classify elements according to their similar properties , one famous trial was that of the Russian scientist Dimitri Mendeleev then Mosley and at last The Modern Periodic Table.


Basic Concepts
The atom is the smallest building unit of an element that can enter a chemical reaction without being changed
And it consists of: The nucleus: In which most of the atomic mass is located and contains two types of particles
Protons: which carry positive charges Neutrons: which are electrical ly neutral Electrons:
Very small particles rotating around the nucleus. The mass of these electronic s is negligible compared with the masses of the protons and neutrons inside the nucleus.
And you learned from your previous studies that: Atomic number: It is the number of protons in the nucleus of an atom of the element. Mass number: It is the sum of the numbers of protons and neutrons in the nucleus of an element. Most of the atomic mass is located in the nucleus An atom is totally neutral since the number of protons (positivel y charged) inside the nucleus equals the number of electrons (negativel y charged) that rotate around the nucleus The nucleus is positively charged
Find the relation between the number of neutrons and the atomic mass
Atomic number = no. of protons = no. of electrons
Mass number = no. of protons + no. of neutrons
no. of neutrons = Mass number - Atomic number


Classifica tion of Elements Scientists tried to classify elements according to their similar properties . One famous trial was that of the Russian scientist Dimitri Mendeleev Mendeleev' s Periodic Table: Is considered as the first table to classify elements. He classified the elements according to their atomic mass. He realized that the properties of elements are repeated in a periodical manner. From its defects is that it did not allow the accurate classifica tion of elements. Mosley's Periodic Table: Mosley studied the properties of the elements and found that their physical and chemical properties are related periodical ly to the atomic number rather than to the atomic mass. He arranged the elements in an increasing atomic numbers and not atomic masses in a manner similar to Mendeleev' s periodic table. The Modern Periodic Table: After the discovery of the new atom structure, its energy shells and distributi on of electrons it became possible to arrange the elements in a periodic system depending on the: Increase in atomic number Filling energy shells with electrons Elements with the same numbers of electrons in their outer shells have similar chemical properties , since these electrons determine the valences of the atoms
The number of elements known so far is approximat ely 112 elements. Among these, 92 elements can be found in nature and the rest of elements are synthetic. (i.e. they can be prepared artificial ly under certain conditions ) 103 of the elements are now arranged in the modern periodic table

The Modern Periodic Table The Modern Periodic Table consists of: 18 vertical groups and 7 horizontal periods Each vertical group contains a group (or family) of elements that exhibit similar properties . In the horizontal periods, each of them contains a number of elements of gradually increasing atomic numbers. The properties of elements within a period vary from left (****llic elements) to right (non - ****llic elements) and each period starts by filling a new energy shell. Periodic Table descriptio n: The vertical groups in the periodic table starts from the left and are given the symbols: 1A , 2A To the right of the table the groups are given the symbols: 3A , 4A , 5A , 6A , 7A The last group to the right contains the inert (or noble) Gases and is known as the zeroth group.
Starting from the period number 4, the vertical groups of the periodic table are split into two become separated by a number of elements called "transitio n elements". These transition elements are themselves classified into vertical groups that are given the symbols: 3B , 4B , 5B , 6B , 7B , 8 , 1B , 2B Group 8 contains three columns of elements. The number of a group: indicates the number of electrons in the outer shell in the atom. The number of a period: indicates the number of energy shells in the atom and is given the numbers.

Element

Period
Number

Number of
Energy shells

Number
Of group

Number of Electrons in the outer shell

Lithium Li

2

2

1

1

Carbon C

2

2

4

4

Oxygen O

2

2

6

6

Sodium Na

3

3

1

1

Aluminium Al

3

3

3

3

Calcium Ca

4

4

2

2

The properties of elements differ gradually: Within a group: The properties of elements within a group differ gradually as we go from top to bottom. For example in group 1A - Which exists to the left of the periodic table and contains the alkali ****ls, all of which are monovalent ****ls - The ****llic properties increase gradually as we go from top to bottom of the group. Therefore, Cesium Cs is the most ****llic whereas Lithium Li is the least ****llic within this group. Francium Fr is a radioactiv e element. Within a period:
o The properties of the elements within a period also differ gradually as we go from left(****l lic elements) to right (non - ****llic elements). Remember that: A group: contains elements with similar chemical properties that differ gradually as we go from top to bottom. A period: contains elements that gradually increase in atomic number. The elements properties gradually differ as we go from left to right.

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