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Periodic Table and Periodicity of Elements (Grade 9 Students)

Periodic table and periodicity of properties

Question 1: Define following terms:
Periodic table; periodic  law; periods of elements; groups of elements; short periods and long periods.
Answer
Periodic table: A table that shows a systematic arrangement of elements is called periodic table.

Periodic law: According to this law, the elements are arranged with increasing order of the atomic numbers their properties are repeated in periodic  manners.

Periods: The horizontal rows of periodic  table are known as periods. 

Short periods: First three periods are called short periods. 

Long periods: Periods number 4, 5, 6 and 7 are called Long periods. 

Groups: The vertical columns of periodic tables are known as groups. All elements are divided into two groups. 

Question 2: Differentiate between normal a Representative elements and transition elements
Answer. 
Normal or Representative elements: Group A elements are called Normal or representative elements. 
Transition elements: Group B elements are called transition elements. 

Question 3: What are alkali metals, alkaline earth metals, halogens and noble gases? 
Alkalie metals: Group IA elements are called alkali metals. 
Alkaline earth metals: Group IIA elements are called alkaline earth metals. 

Halogens: Group VIIA elements are called halogens. 
Noble gases: group VIIIA elements are called noble gases. 

Question 4: Differentiate between s-block and p- block elements. 

Answer 

s-block elements: Elements of IA and IIA groups are called a-block elements. 
p-lock elements: The elements of III-A group to VIIIA elements are called p-Block elements. 

Question 5: what is shielding effect? give its friend in the periodic table. 
Answer. 
Shielding effect: The decrease in force of attraction between nucleus and the valence electrons due to to inner shell electron is called shielding effect.
Trend in Periodic Table

Question 6: What is atomic size? Describe its trend in periodic table with reason. 
Answer. 
Atomic size: Average distance between nucleus of an atom and its valence shell is called atomic size
Trend in Periodic Table
In period:
Atomic size decreases from left to right in the period. 
Reason:  As we move from left to right across the period, valence shall remains the same. At the same time, the positive charge of nucleus goes on increasing. As a result force of attraction between nucleus and valence electron also increases. Therefore, atomic size decreases. 
In group: 
Atomic size increases from top to bottom of a group. 

Reason: Size of atom is determined from size of valence shell. As we move from top to bottom along a group, each atom has an additional shell of electrons. This increases size of valence shell. Hence, size of atoms also increases. 


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  1. RabiaOctober 14, 2019 at 5:39 PM

    This comment has been removed by a blog administrator.

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  2. yaseenJanuary 8, 2020 at 9:22 AM

    The simplest and easiest notes for matric students. Thanks sir, we need more notes of chemistry.

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