Hushar Mulga
@Rohit

Chapter 2Periodic Classification Of Element

Spread the love

Chapter 2 Periodic Classification Of Element

Q. 1. Rearrange the columns 2 and 3 so as to match with the column 1.

Column 1 Column 2 Column 3
i. Triad a. Lightest and negatively charged particle in all the atoms 1. Mendeleev
ii. Octave d. Properties of the eighth element similar to the first 2. Thomson
iii. Atomic number b. Concentrated mass and positive charge 3. Newlands
iv. Period f. Sequential change in molecular formulae 4. Rutherford
v. Nucleus e. Positive charge on the nucleus 5. Dobereiner
vi. Electron c. Average of the first and the third atomic mass 6. Moseley
Column I
Column II
Column III
i. Triad c. Average of the first and the third atomic mass 5. Dobereiner
ii. Octave d. Properties of the eight-element similar to the first. 3. Newlands
iii. Atomic Number e. Positive charge on the nucleus. 6. Moseley
iv. Period f. Sequential change in molecular formulae 1. Mendeleev
v. Nucleus b. Concentrated mass and positive charge 4. Rutherford
vi. Electron a. Lightest and negatively charged particle in all the atoms 2. Thomson
  1. Choose the correct option and rewrite the statement.

a. The number of electrons in the outermost shell of alkali metals is……
(i) 1 (ii) 2 (iii) 3 (iv) 7

Answer:- 1 . Akali metals comes under group 1 and number of electrons in the outermost shell of group 1 element is 1

b. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in …..

i) Group 2 (ii) Group16
(iii) Period 2 (iv) d-block

Answer:_ 1) Group 2

c. Molecular formula of the chloride of an element X is XCl. This compound is a solid having high
melting point. Which of the following elements be present in the same group as X.

(i) Na (ii) Mg (iii) Al (iv) Si

Ans:- (1) Na

d. In which block of the modern periodic table are the nonmetals found?
(i) s-block (ii) p-block
(iii) d-block (iv) f-block

Answer:- P- Block

  1. An element has its electron configuration as 2,8,2. Now answer the following questions.

a. What is the atomic number of this element?

Answer:– 12

b What is the group of this element?

Answer:_ 2

C. To which period does this element belong?

Answer:- 3 rd period

d. With which of the following elements would this element resemble? (Atomic numbers are
given in the brackets)
N (7), Be (4) , Ar (18), Cl (17)

Answer:- Be (4)

4. Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.

a. 3Li, 14Si, 2He, 11Na, 15P Which of these elements belong to be period 3?

Answer:_ Among the given elements, Na(2,8,2), Si(2,8,4) and P(2,8,5) belong to group 3. Because in these elements, total three shells are present. Thus, these elements belong to group 3.

b. 1H, 7N, 20Ca, 16S, 4Be, 18Ar Which of these elements belong to the second group?

Answer:- Among the given elements, Ca and Be belong to second group. Because both has two electrons in the outermost shell. Thus, these two elements belong to second group.

c. 7N, 6C, 8O, 5B, 13A1 Which is the most electronegative element among these?

Answer:- Among the given elements, oxygen is the most electronegative element.

d. 4Be, 6C, 8O, 5B, 13A1 Which is the most electropositive element among these?

Answer:- Among the given elements, Al has the highest electropositive character

e. 11Na, 15P, 17C1, 14Si, 12Mg Which of these has largest atoms?

Answer:- Among the given elements, Na is the element which has largest atoms.

f. 19K, 3Li, 11Na, 4Be Which of these atoms has smallest atomic radius?

Answer:- Among the given elements, Be has the smallest atomic radius.

g. 13A1, 14Si, 11Na, 12Mg, 16S Which of the above elements has the highest metallic character?

Answer:- Among the given elements, Na has highest metallic character (most electropositive element)

h. 6C, 3Li, 9F, 7N, 😯 Which of the above elements has the highest nonmetallic character?

Answer:- Among the given elements, fluorine has highest non-metallic character (most electronegative element).

  1. Write the name and symbol of the element from the description.

a. The atom having the smallest size.

Answer:- a. The atom with the smallest size is hydrogen. The symbol of the hydrogen atom is 1H.

b. The atom having the smallest atomic mass.

Answer:- The atom with the smallest atomic mass is Hydrogen. The symbol of the helium atom is 1H.

c. The most electronegative atom.

Answer:- The most electronegative atom is fluorine

The symbol of the fluorine atom is 9F.

d. The noble gas with the smallest atomic radius.

Answer:- The noble gas with the smallest atomic radius is Helium. The symbol of the hydrogen atom is 1H.

e. The most reactive nonmetal

Answer:- The most reactive non-metal is fluorine

The symbol of the fluorine atom is 9F.

6 Write short notes.

a. Mendeleev’s periodic law.

answer:-

  1. Properties of elements follow a periodic pattern based on their atomic masses.
  2. Mendeleev arranged elements by their properties and increasing atomic weights.
  3. Vertical columns in the periodic table are called groups and horizontal rows are called periods.
  4. Mendeleev left spaces in the table for undiscovered elements and later updated it with rediscovered atomic masses.

b. Structure of the modern periodic table.

Answer:-

  1. he periodic table has horizontal periods 1 to 7.
  2. The periodic table has vertical groups 1 to 18.
  3. Atomic numbers are located at the top of each element box.
  4. The bottom of the periodic table has two rows, the lanthanide and actinoid series.
  5. There are 118 boxes in the periodic table.
  6. The periodic table is divided into four blocks: s-block, p-block, d-block, and f-block.
  7. The first period contains two elements.
  8. The s-block includes alkali and alkaline earth metals, p-block includes metals, non-metals and metalloids, d-block includes transition metals, and the f-block includes the lanthanide and actinoid series.

c. Position of isotopes in the Mendeleev’s and the modern periodic table.

Answer:-

  1. Some atoms in certain elements have the same atomic number but different atomic mass number and are called isotopes of that element.
  2. Isotopes were discovered after Mendeleev’s discovery of the periodic table.
  3. Isotopes have different atomic masses but the same chemical properties.
  4. Therefore, isotopes of an element are placed in the same place on the periodic table as the element, rather than each isotope having its own separate place.

7 Write scientific reasons.

a. Atomic radius goes on decreasing while going from left to right in a period.

Answer:-

Atomic radius decreases from left to right within a period because of following reason

T1 he atomic number increases by one in a period, resulting in an increase in nuclear charge.

2 The outer electrons are added to the same valence shell.

3 The increased nuclear charge leads to an increased attraction of electrons by the nucleus.

4 As a result, the size of the atom decreases with an increase in the atomic number (number of protons).

b. Metallic character goes on decreasing while going from left to right in a period.

Answer:_ Metallic character goes on decreasing while going from left to right in a period because:

  1. Metals have a tendency to lose their valence electrons and form a cation.
  2. The nuclear charge increases from left to right in a period as the atomic number increases.
  3. This increase in nuclear charge increases the force of attraction of electrons by the nucleus.
  4. As a result, the tendency to lose electrons decreases.
  5. Hence, the metallic character decreases within a period.

c. Atomic radius goes on increasing down a group.

Answer:- Atomic radius goes on increasing down a group because

  1. The atomic number increases one by one going down a group, resulting in an increase in nuclear charge.
  2. The outer electrons are added to a new valence shell.
  3. As a result, the distance between the outermost electron (valence electron) and the nucleus increases.
  4. Hence, the size of the atom increases with an increase in atomic number.

d. Elements belonging to the same group have the same valency.

Answer:- Elements belonging to the same group have the same valency because:

  1. The valency of an element can be determined by counting the number of electrons in the outermost shell.
  2. The group number of an element can also be determined by its valency.
  3. If the valency of an element is one, it belongs to group 1.
  4. If the valency of an element is two, it belongs to group 2, and so on.

e. The third period contains only eight elements even through the electron capacity of the third shell is 18 .

Answer :-

  1. 8 elements in the third period, despite the third shell having a capacity of 18 electrons.
  2. Knowledge of electron capacity in the K, L, M, and N shells.
  3. Several factors impact the filling of electrons.
  4. 8 elements in the third period due to the law of electron octet, with atoms striving for 8 electrons in the outer shell to attain a noble gas configuration and extra electrons moving to the next shell.

8 Write the names from the description.

a. The period with electrons in the shells K, L and M.

Answer:_ Third period It is given that the electrons are present in shells K,L and M. This means there are total three shells present. Thus, third period is having elements which are electrons present in K,L and M.

Element Atomic Number Electronic Configuration
Lithium 3 1s2 2s1
Beryllium 4 1s2 2s2
Boron 5 1s2 2s2 2p1
Carbon 6 1s2 2s2 2p2
Nitrogen 7 1s2 2s2 2p3
Oxygen 8 1s2 2s2 2p4
Fluorine 9 1s2 2s2 2p5
Neon 10 1s2 2s2 2p6

b. The group with valency zero.

Answer:- Group-8 (Noble gases) In the noble gases, there are no valence electrons present. The atoms of the noble gases have noble gas configuration as shown below in the table:

Element Name Symbol Atomic Number Electronic Configuration
Helium He 2 1s2
Neon Ne 10 1s2 2s2 2p6
Argon Ar 18 1s2 2s2 2p6 3s2 3p6
Krypton Kr 36 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
Xenon Xe 54 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6
Radon Rn 86 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6
Oganesson Og 118 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6

c. The family of nonmetals having valency one

Answer:- The family of nonmetals having valency one are: ⇒ Fluorine ⇒ Chlorine ⇒ Bromine ⇒ Iodine

d. The family of metals having valency one

The family of metals having valency one are (alkali metals): ⇒ Lithium ⇒ Sodium ⇒ Potassium ⇒ Rubidium ⇒ Cesium ⇒ Francium

e. The family of metals having valency two

Answer:_

The family of metals having valency two are (alkaline earth metals). ⇒ Beryllium ⇒ Magnesium ⇒ Calcium ⇒ Strontium ⇒ Barium ⇒ Radon

f. The metalloids in the second and third periods.

Answer:- Second period and third period contain metalloids which are Boron and Silicon respectively. These are the elements having properties intermediate of metals and non-metals.

g. Nonmetals in the third period.

Answer:_ Non-Metals present in 3rd Period are :- Phosphorous, Chlorine and Sulfur

h. Two elements having valency 4.

Answer:_ Two elements having valency four are 14 Si (silicon) and 6C (carbon)

Chapter 2Periodic Classification Of Element