Periodic Classification of elements chapter 2 notes of science 1 for SSC class 10 board exam. Notes are very essential part of study for the preparation of SSC Board exam and obtain maximum score in board exam.
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| Modern periodic table |
Periodic Classification of Elements notes for SSC class 10 Board Exam.
Structure of Modern Periodic Table.
The modern periodic table contains 7 horizontal rows called periods (1 to 7). Similarly, the 18 vertical columns in this table are called groups (1 to 18). Two rows are shown separately at the bottom of the periodic table are called the Lanthanide series and Actinide series respectively. These are 118 boxes in the periodic table including the two series. The entire periodic table is divided into four blocks.
- 's' block.
- 'p' block.
- 'd' block.
- 'f' block.
The s block contains groups 1 to 2. The groups 13 to 18 configure the p block. The groups 3 to 12 are constituted by d block is called Transitional elements. The lanthanide and Actinide series construct the f block at the bottom. A zigzag line can be shown the three traditional types of elements.
- The metalloid elements are on the border of the zigzag line.
- All the metals repose on the left side of the zigzag line.
- All the nonmetals lie on the right side of the zigzag line.
The characteristics of groups and periods of Modern Periodic Table.
- The elements in a group show the resemblance and degeneration in their properties.
- The properties of elements change slowly while going from left to right in a particular period.
- It is the electronic configuration of an element that decides the group and the period in which it is placed.
- Period and Groups
7 horizontal rows called periods (1 to 7 ). Similarly, the 18 vertical columns in the modern periodic table are called groups (1 to 18).
The classification of elements in the modern Periodic Table is intended on the enlarging order of their atomic number.
As a result, most of the drawbacks of the Mendeleev periodic table are to be removed. however, the obscurity about the position of hydrogen is not removed even in the modern periodic table.
What are the attributes (fundamental features) of the modern periodic table?
- Elements are organized in increasing order of their atomic numbers.
- Vertical columns are called groups. There are 18 groups. The chemical properties of the elements in the same group show similarity and spectrum.
- Horizontal raw is called periods. there are in all seven periods. The properties of elements change slowly from one end to another end in a period.
- In the Modern Periodic Table, electrons are fitted in the same shell while going along a period from left to right. At the beginning of the next period, a new electron shell starts feeling up.
- The number of elements in the first three periods is determined by the electron capacity of the shell and the roar of the electron octet.
- When the properties of elements in a periodical group of the modern periodic table are balanced, certain regularity is observed in their modification. It is called periodic trends.
- First of all, in the modern periodic table, the periodic trends have only three properties of elements namely valency, atomic size, and metallic non-metallic characters.
Why does the atomic radius go on diminishing while going from left to right?
- While going from left to right within a period, atomic number increases only one by one. This means that the positive charge on the nucleus increases by one unit at a time.
- However, the additional electron gets added to the same outermost shell. Due to the increased nuclear charge, the electrons are pulled towards the nucleus to a greater extent. As a result, the size of an atom decreases and also atomic radius.
Why does atomic size go enlarging while going down in a group?
- Because, as we go down in a group, a new shell is added. Therefore, the distance between the outermost electron and the nucleus goes on enlarging. As a result of these, that makes size increases despite the increased nuclear charge.
- Size or volume is a functional and fundamental property of matter. The size of an atom is denoted by its radius. The distance between the nucleus of the atom and its outermost shell is the atomic radius.
- Atomic radius is illustrated in the unit Picometer ( PM ). It is smaller than Nanometer (NM)(1 pm= 10^-12 m).
Do the elements belonging to the same group have the same valency?
- The valency of an element is determined by the number of valence electrons in the outermost shell of an atom of an element.
- All the elements in a group have the same number of valence electrons.
- Therefore, elements in the same group should have the same valency. For example, the elements of group 1 contains only one valence electron. The valency of electron elements of group 1 is 1. Similarly, for group second, the valency is 2.
Why do the third period contains only 8 elements even though the electron capacity of the third shell is 18?
- In the modern periodic table, elements are arranged in an increasing order of their atomic numbers in a period. The third row contains 8 elements and the electron capacity of the third shell is 18.
- In the third period, while moving from left to right, atomic number increases and number of electrons also increases in the shell.
- The number of elements present in third period is decided on the basis of the electronic configuration and octet rule.
What are the merits of Mendeleev's periodic table?
- Characteristics of science:
Science is a process and has the freedom to revise the old inference by using more advanced means and methods of doing experiments. It is seen in Mendeleev's periodic table.
- Proper places:
Atomic masses of some elements were revised to give them a proper place in the periodic table following their properties.
- Vacant places:
Mendeleev kept vacant places for the elements not discovered till then in the periodic table. Why?
- No places reserved for noble gases:
There were no places reserved for noble gases in Mendeleev's periodic table. But Mendeleev organized the zero group without disturbing the original periodic table in which noble gases were fitted very well towards the end of the 19th century.
Mendeleev's periodic table
The Russian scientist, Dmitri Mendeleev, developed the periodic table of elements during the period 1869 to 1872 A.D. He created the periodic table based on the chemical and physical properties of the elements which are the molecular formula of hybride and oxide of the elements, melting & boiling points and density of the elements with their atomic mass. He also selected that the element which has similar physical and chemical properties repeat after a definite interval. That is, the properties of elements are periodical functions of their atomic masses.
What are the demerits of Mendeleev's periodic table?
- Ambiguity:-
There was ambiguity regarding their sequence in Mendeleev's periodic table as the atomic mass of element Cobalt (Co) and nickel (Ni).
- No place for isotopes:
Isotopes were discovered long times after Mendeleev put forth the periodic table. (Isotopes have the same chemical properties, but the different atomic mass is called isotopes.)
Increasing order of atomic masses does not appear to be uniform. Why?
It was not possible to predict how many elements could be discovered between heavy elements when elements are arranged in increasing order of atomic masses.
Position of hydrogen:
Hydrogen shows similarity with halogen. In the same way, there are some similarities in the chemical properties of alkali metals. Therefore, it cannot be decided the correct position of the hydrogen.
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