OMTEX CLASSES: Periodic Classification of Elements.Chapter No. 2, SSC Science and Technology

Periodic Classification of Elements.Chapter No. 2, SSC Science and Technology

Periodic Classification of Elements

SCIENCE & TECHNOLOGY PART 1

CHAPTER NO. 2

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

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


Ans. (i – c – 5 ) , (ii – d – 3) , (iii – e – 6 ) , (iv – f – 1) , (v – b – 4), (vi - a – 2).
2. 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
b. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in ………………

           i. Group 2
           ii. Group 16
           iii. Period 2          
           iv. d – block.
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
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.
3. An element has its electronic configuration as 2, 8, 2. Now answer the following questions.

a. What is the atomic number of this element?

Answer. The atomic number of this element is 2 + 8 + 2 = 12.
b. What is the group of this element.

Answer. The electronic configuration of the given element is 2, 8. 2 which shows that this element has 2 valence electrons. Hence the given element is placed in group 2.
c. To which period does this element belong?

Answer. The electronic configuration of the given element is 2, 8, 2 which shows that the electrons are arranged in 3 shells. Hence the given element is placed in third 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. Electronic Configuration:
N (7) – 2 , 5         Be (4) – 2, 2 Ar (18) – 2 , 8, 8    Cl (17) – 2, 8, 7
The element Beryllium (Be) has valence electron 2 just like the given element. Hence this element will be chemically similar to the given element which has the same number of valence electrons in its atoms.

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

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

a. The atom having the smallest size.

Answer. Hydrogen (H)

b. The atom having the smallest atomic mass.

Answer. Hydrogen (H)

c. The most electronegative atom.

Answer. Fluorine (F)

d. The noble gas with the smallest atomic radius.

Answer. Helium. (He)

e. The most reactive nonmetal.

Answer. Fluorine. (F)


6. Write short notes:

a. Mendeleev’s Periodic law.

Answer. 1. The Russian Scientist Dmitri Mendeleev developed the periodic table of elements during the period 1869 to 1872 A.D.

2. Mendeleev organized the periodic table on the basis of the chemical and physical properties of the elements. He considered the fundamental property of elements, namely the atomic mass as standard and arranged 63 elements known at that time in an increasing order of their atomic masses.

3. He found that the elements with similar physical and chemical properties repeat after a definite interval.

4. On the basis of this finding, he stated that ‘properties of elements are a periodic function of their atomic masses’. This is known as Mendeleev’s periodic law.

b. Structure of the Modern Periodic Table.

Answer. 1. The modern periodic table consists of 7 horizontal rows called the periods and 18 vertical columns called the groups.

2. Apart from these seven rows, two rows are shown separately at the bottom of the periodic table. These are called lanthanide series and actinide series respectively.

3. The entire periodic table is divided into four blocks:

s - block: Contains group 1 and 2 elements.
p - block: contains group 13 to 18 elements.
d- block: contains group 3 to 12 elements. (Transition elements)
f - block: Two rows are shown separately at the bottom of the periodic table. Contains lanthanide and actinide series.

4. A zig - zag line is drawn in the p - block of the periodic table. Metals lie on the left side while nonmetals lie on the right side of this zig - zag line. Metalloids lie along the border of this line.

c. Position of isotopes in the Mendeleev’s and the Modern Periodic Table.

Ans. 1. Isotopes were discovered long time after Mendeleev developed the periodic table. All isotopes of the same element have different atomic masses but same atomic number. They have similar chemical properties.

2. As isotopes have the same chemical properties but different atomic masses, a challenge was posed in placing them in Mendeleev’s periodic table.

3. In Mendeleev’s periodic table, elements are arranged in increasing order of their atomic masses such that chemically similar elements are placed together in a group.

4. So, it became difficult to place isotopes in Mendeleev’s periodic table. Therefore, isotopes were not given separate place in Mendeleev’s periodic table.

5. In Modern periodic table, elements are arranged in increasing order of their atomic number. Hence, all the isotopes of an elements occupy the same position in the modern periodic table.
Important Extra Questions, on this chapter that may come in your Board Exam.

GIVE SCIENTIFIC REASONS













ANSWER THE FOLLOWING











Why is atomic number said to be a fundamental property?


What should be the position of Hydrogen in the Modern Periodic Table ? Why?

 

The atomic number of an element X is 17. Predict :


Read the following descriptions and decide whether the element belongs to metal or non-metal. Justify your answer.


How do you calculate valency of an element from its electronic configuration ?


How are isotopes of different elements placed in the Modern Periodic Table ?


Explain the zig-zag line in the periodic table.






Explain the features of Mendeleev's periodic table.