# Classification Of Elements: Class 10 Science Notes

Classification Of Elements Class 10 Science Complete Notes. This note include all the excercise given in Classification Of Elements chapter of science book such as question answer, numericals, give reason, diagrammatic questions and define the following. This note is published for helping students to solve their problems.

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## Chapter - 7  Classification Of Elements

### 2. Differentiate Between.

a. Group and Period

Ans: The difference between group and period are as follows:

HTML Table Generator
Groups Periods
The columns of the periodic table called are groups.  The rows of the periodic table are called periods.
All the elements in same group have the same number of valence electron. The valence electron of elements in same period increases from left to right.
The elements in each groups have similar properties. The elements in same period has different properties
There are 18 groups   There are 7 periods

b. Short period and long period

Ans: The difference between short period and long period are as follows:

HTML Table Generator
Short Period  Long Period
The second and third period of perodic table is known as short periods. The fourth and fifth periods of perodic table is known as Long periods
It Contains 8 elements in each period. It contains 18 elements in each period.

c. S-block Elements and P-block Elements

Ans: The difference between S-block Elements and P-block Elements are as follows:

HTML Table Generator
S block Elements  P block Elements
The S-black elements have
s-sub shell as the last orbital
The P-block elements have p-sub shell as the last orbital
They can have only 1 or 2 electrons in the last sub-shell They can have 1 to 6 electrons in the last sub-shell

d. Mendeleev periodic table and Modern Perodic table

Ans: The difference between Mendeleev periodic table and Modern Perodic table are as follows:
HTML Table Generator
Mendeleev Perodic table  Modern Perodic table
Elements are arranged in the ascending order of their atomic mass Elements arranged in the ascending order of their atomic number
The number of classified elements is less The number of classified elements is more
Has no seperate place for lanthanides and actinides Has seperate place for lanthanides and actinides
There are 8 groups There are 18 groups

### 3. Give Reason.

a. Argon is an inert gas.

Ans: Argon is an inert because it has 8 electrons in it's valence shell and it doesn't take part in chemical reaction.

b. The valency of nitrogen is 3.

Ans: The valency of nitrogen is 3 because it has 5 electrons in its valence shell. It can easily gain 3 electrons to attain stable electronic configuration.

c. Chlorine is an active non-metal.

Ans: Chlorine is an active non metal because its atomic mass is less and contains 7 electrons in it's valence shell. It shows the tendancy of gaining one electron from other atom to attain stable electronic configuration.

d. Fluorine is more reactive than chlorine.

Ans: Fluorine is more reactive than chlorine because fluorine has less atomic mass due to which it has greater force of attraction and can easily gain 1 electron to become stable.

e. Sodium is less reactive than potassium.

Ans: Sodium is less reactive than potassium because the atomic size of sodium is small than potassium. So, sodium has greater force of attraction between its electron and nucleus and it is unable to loose it's electron easily.

f. The members of group IA are called alkali metals.

Ans: The members of group IA are called alkali metals because they contain 1 valence electron and can easily form alkalies (water soluble base) when react with water.

g. The group I elements are very active.

Ans: The group I elements are very active because they all have one valence electron due to which they can easily loose the electron to become stable.

h. Lanthanides and actinides are kept seriously separately in the modern perodic table.

Ans: Lanthanides and actinides are kept separately in the modern perodic table because they all are inner transition metals and keeping them separately helps to save space and avoid undue sidewise expansion of the perodic table.

i. Transition elements have variable valency.

Ans: Transition elements have variable valency because their outmost and second outmost shell are partially filled due which electron can easily travel from one shell to another.

j. Halogens are active non-metals.

Ans: Halogens are active non-metals because they have seven valence electrons and can easily gain one electron to become stable.

a. What is perodic table?

Ans: The systematic arrangement of elements on the basis of similarities of electronic configuration into groups and periods is called perodic table.

b. State Mendeleev's perodic law.

Ans: Mendeleev's perodic law states that " Physical and chemical properties of elements are the perodic functions of their atomic weights.

c. What are the merits of Mendeleev's perodic table?

Ans: The merits of Mendeleev's perodic table are as follows:

• It helps in the systematic and scientific study of the elements
• He classified all the known 63 elements at that time
• He left some gaps for the undiscovered elements and Predicted the properties of unknown elements
• It helps chemists to discover new elements as he lebt some gaps for them
• Nobel gases could accommodate in a new group in Mendeleev's perodic table without disturbing the existing order after discovery

d. What are the defects of Mendeleev's perodic table?

Ans: The defects of Mendeleev's perodic table are as follows:

• Position of hydrogen
• Separation of chemically similar elements
• Grouping of chemically disimilar elements
• Position of isotope
• Anamalous of elements Pair
• Position of lanthanide and actinides
• Position of metals, non-metals and metalloids.

e. State modern perodic law.

Ans: Modem perodic law state that," the physical and the chemical properties of elements are perodic function of their atomic numbers"

f. What are the features of modern perodic table?

Ans: The features of Modern Perodic table are as follows:

• Elements are arranged in the increasing order of atomic number
• It separates metals from non-metals
• It has 7 periods and 18 groups
• The groups of the modern perodic table is divided into sub groups
• The representative and transition elements have been seperated in the modem perodic table

g. How is the modern perodic table superior to Mendeleev's table?

Ans: Modern perodic table is superior to Mendeleev's perodic table because modern perodic table is based on the atomic number which is more fundamental than atomic mass. It has also removed all the drawbacks of mendeleev's perodic table.

h. Why are Li, Na and K placed in the same group of perodic table?

Ans: Lithium, Sodium and Potassium are placed in the same groups of the perodic table because they are alkali metals having 1 valence electron. They all show similar chemical properties.

i. Name two alkaline earth metals.

Ans: The two alkaline earth metals are as follows:

• Calcium
• Beryllium

j. What do you mean by P-block elements? Write any five examples of this block.

Ans: P - block elements are those elements which have P-subshell as the last orbitals.
The five examples of this block are as follows:

• Carbon
• Oxygen
• Nitrogen
• Aluminium
• Chlorine

k. Define

i. Group

Ans: The vertical columns of the perodic table is known as groups.

ii. Period

Ans: The horizontal rows of the perodic table is known as periods.

iii. Perodic table

Ans: The systematic arrangement of elements on the basis of their similar characteristics into groups and periods is known as Perodic table.

iv. Isotopes

Ans: The atoms of the same elements having equal atomic number but a different mass number are called isotopes.

v. Sub-shell

Ans: The region around the nucleus where the probability of finding electrons is maximum is called sub-shell.

vi. Transition elements

Ans: Transitions elements are those elements which fall under d-block elements.

l. What factors do the valencies of elements depend upon?

Ans: The valencies of elements depend on the maximum number of electrons present in it's last shell and the number of electrons which take part in chemical reaction.

### 5. Diagrammatic Questions

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