CLASSIFICATION OF ELEMENTS-THE PERIODIC TABLE Questions

CLASSIFICATION OF ELEMENTS

THE PERIODIC TABLE

1⁄2 Mark Questions

1. Define Dobereiner's triad.

Ans: Triad: A group of three elements with similar chemical properties is known as a triad.

2. Give an example of Dobereiner's triads.

Ans: Li, Na, K

3. How many elements are present in the first period?

Ans: 2 elements (H, He)

4. How many elements are present in the 2nd (or 3rd) period?

Ans: 8 elements

5. How many elements are present in the 4th (or 5th) period?

Ans: 18 elements

6. How many elements are present in the 6th period?

Ans: 32 elements

7. What is the melting point of Galium?

Ans: 30.2°C

8. Who proposed the law of Octaves?

Ans: New Lands

9. What are s- block elements?

Ans: Elements belonging to I A, II-A Groups are called s - block elements.

10. Which group elements are called p- block elements?

Ans: Elements from group III-A to group VIII A are called p- block elements.

11. Which group elements are called d- block elements?

Ans: Elements from group I B to group VIII B are called d- block elements.

12. What are f- block elements?

Ans: Lanthanoids and actinoids are known as f-block elements.

13. Which elements are called transition elements?

Ans: All the d- block elements (except the Zn group) are known as transition elements.

14. Which elements are called inner transition elements?

Ans: All the f-block elements (both Lanthanides, Actinides) are known as inner transition elements.

15. What are representative elements?

Ans: s, p block elements are known as representative elements.

16. What are alkali metals?

Ans: Group I A elements are called alkali metals.

17. What are alkali earth metals?

Ans: Group II-A elements are called alkali earth metals.

18. This is not a Dobereiner's triad

A) Li, Na, K B) Mn, Cr, Fe C) Cu, Hg, Mg D) S, Se, Te

Ans: C) Cu, Hg, Mg

19. Group-18 (VIIIA) elements are called

A) Carbon family B) Chalcogen family C) Halogen family D) Noble gas family

Ans: D) Noble gas family

20. Which one of the following elements belongs to the 3rd period and III-A group?

A) sodium B) Potassium C) Aluminium D) Argon

Ans: C) Aluminium

21. An example for Mandeleev's anomalous series

A) Tellurium, Iodine B) Sodium, Potassium C) Eka Boron, Eka silicon D) Sodium, Calcium

Ans: A) Tellurium, Iodine

22. Electron configuration of an atom is 2, 8, 7 to which of the following elements would it be

chemically similar?

A) nitrogen(Z=7) B) fluorine(Z=9) C) phosphorous(Z=15) D) argon(Z=18)

Ans: B) fluorine(Z=9)

23. Which of the following is the most active metal?

A) lithium B) sodium C) potassium D) rubidium

Ans: D) rubidium

24. Which of the following is Mandeleeff’s eka – aluminum

A) Scandium B) Zinc C) Gallium D) Germanium

Ans: C) Gallium

25. Mandeleeff arrange the periodic table based on ---------- of the elements.

A) Atomic weight B) Atomic radius C) Size of the element D) None of these

Ans: A) Atomic weight

26. Which of the following is Mandeleeff’s eka – boran

A) Scandium B) Zinc C) Gallium D) Germanium

Ans: A) Scandium

27. Mandeleeff’s eka-silicon is

A) Scandium B) Zinc C) Gallium D) Germanium

Ans: D) Germanium

1 Mark Questions

1. What is modern periodic law. (OR)

Define Moseley's periodic law.

Ans: Modern periodic law: “The physical and chemical properties of elements are the periodic function of the electronic configurations of their atoms.”

2. State the Newlands law of octaves?

Ans: Newlands law of octaves: When elements are arranged in the ascending order of their atomic weights, every eighth element starting from a given element resembles in its properties to that of the starting element.

3. What is Mendeleev's periodic law?

Ans: Mendeleev periodic law: “The physical and chemical properties of the elements are the periodic function of their atomic weights.”

4. An element has the atomic number 17.

Where would you expect this element in the periodic table? Why?

Ans: 1. Electronic configuration of the the given element is 1s2 2s2 2p6 3s2 3p5.

         2. Due to the valency electronic configuration, it belongs to the 3rd period and 17th group.

5. How do you appreciate the special nature of inert gases?

Ans: 1. I appreciate the special nature of inert gases.

2. Because it helps us in explaining the formation of chemical bonds among the atoms of elements

and their stability.

6. A teacher asked to give an example for Dobereiner's triad. Ramu wrote them as “Li, Na, Mg”.

In these three, identify which element does not belong to this triad.

Ans: Mg (magnesium)

7. Which group elements are called the Carbon family?

Ans: 14 (or) IVA group of elements are called Carbon family.

8. How does the ionization energy vary in a group and a period?

Ans: 1. In a group, the ionization energy decreases as we go from top to bottom.

2. In a period the ionization energy increases as we move from left to right.

9. Which elements are called lanthanides?

Ans: Lanthanides: The ‘4f’ elements are called Lanthanoids or lanthanides. They are from 58Ce to 71Lu.

10. Which elements are called Actinides?

Ans: Actinides: The '5f' elements are called Actinoids or Actinides. They are from 90Th to 103Lr.

2 Mark Questions

1. Name two elements that you would expect to have chemical properties similar to Mg. What is the basis for your choice?

Ans: 1. The two elements that have chemical properties similar to Mg are Be and Ca.

2. Be, Mg, and Ca belong to same group i.e. group II A.

3.The outermost shell of these three atoms consists of 2 electrons.

4. These three elements have the same type of electronic configuration for their outer shell.

5. So these three elements have same chemical properties. 

2. All alkali metals are solids but hydrogen is a gas with diatomic molecules. Do you justify the inclusion of hydrogen in first group with alkali metals?

Ans: 1.Hydrogen element can be placed in group- 1 along with alkali metals.

2. Also it can be placed in group- 17, along with halogens because it is one electron short of inert gas configuration.

3. But the electronic configuration of hydrogen is 1s2.

4. On the basis of electronic configuration, it should be placed top of the 1st group.

3. Why Lanthanoids and Actinoids placed separately at the bottom of the periodic table?

Ans: 1. The 'f' block elements are called as Lanthanoids and Actinoids.

2. It is not possible to fit these elements in the general periodic table.

3. So they are shown separately at the bottom of the periodic table.

4. State and explain Dobereiner's law of triads with two examples.

Ans: Dobereiner's law of triads: When elements with similar properties are taken three at a time and arranged

 in the ascending order of their atomic weights, the atomic weight of the middle element is the average of the atomic weights of the first and third elements. 

 

This statement is called the Dobereiner’s law of triads.

 

Ex:

1 Lithium (Li)

 7.0

Sodium (Na)

 23.0

Potassium (K)

 39.0



7+39/2 = 23.0

2 Calcium (Ca)

 40.0

Strontium (Sr)

 87.5

Barium (Ba)

 137.0         

40+137 / 2 = 88.5

5. An element has atomic number 19. Where would you expect this element in the periodic table and why?

Ans: 1. The electronic configuration of the element with atomic number 19 is

 1s2 2s2 2p6 3s2 3p6 4s1.

2. The differentiating electron enters the 4th shell. So it belongs to 4th period.

3. The differentiating electron is in the 's' orbital. It means it belongs to s -block.

4. The outer most orbital has only one electron. So it belongs to first group.

5. So this element will be in the 4th period and 1st group of the periodic table.

6. The electronic configuration of the elements X, Y and Z are given below.

 a) X = 2 b) Y = 2, 6 c) Z = 2, 8, 2

i) Which element belongs to second period?

ii) Which element belongs to second group ?

 iii) Which element belongs to 18th group?

Ans: i) Y belongs to 2nd period.

 ii) Z belongs to 2nd group.

 iii) X belongs to 18th group.

7. Why Mendeleev had to leave certain blank spaces in his periodic table? What is your explanation for this?

Ans: 

1. Based on the arrangement of the elements in the table, Mendeleev predicted that some elements were

 missing and left blank spaces at the appropriate places in the table.

2. Mendeleev believed that some new elements would be discovered definitely.

3. He predicted the properties of these new additional elements in advance purely depending on his table.

4. His predicted properties were almost the same as the observed properties of those elements after their discovery.

4 Mark Questions

1. What are the limitations of Mendeleeff’s periodic table? How could the modern periodic table overcome the limitations of Mendeleeff’s table?

Ans: Limitations of Mendeleef's periodic table:

1. Anomalous pair of elements: Certain elements of highest atomic weights precede those with lower atomic weights.

 Ex: tellurium (atomic weight 127.6) precedes Iodine (atomic weight 126.9).

2. Dissimilar elements placed together: Elements with dissimilar properties were placed in same group

 as sub-groups A and B.

 Ex: 'Cl' is of VIIA group and 'Mn' is of VIIB. But Chlorine is a non-metal and Manganese is a metal.

Rectification of problems by Modern periodic table:

1. The periodic law is changed from atomic weight concept to atomic number concept in the modern

 periodic classification

2. In modern periodic table justified the atomic numbers of tellurium is 52 and that of iodine is 53.

3. So the modern periodic table changed their places in groups and periods.

4. Dissimilar elements were placed in different groups

2. Define the modern periodic Law. Discuss the construction of the long form of the periodic table.

Ans: Modern periodic law: “The physical and chemical properties of elements are the periodic function of the electronic configurations of their atoms.”

Construction of the long form of the periodic table:

1. The modern periodic table has 18 vertical columns and 7 horizontal rows.

2. Vertical columns are known as groups and the horizontal rows are called as periods.

3. Depending upon to which sub-shell the differentiating electron. i.e., the last coming electron enters in the

 atom of the given element, the elements are classified as ‘s’ ‘p’, ‘d’ and ‘f’ block elements.

4. The first period contains only two elements Hydrogen (H), Helium (He).

5. The 2nd and 3nd periods contain 8 elements each.

6. The 4th and 5th periods contain 18 elements each.

7. There are 32 elements in the 6th period.

8. The 7th period is incomplete.

9. The f- block elements known as lanthanoids and actinoids are shown separately at the bottom of the periodic table.

10. Inert gases are placed in 18th group.

3. Explain how the elements are classified into s, p, d and f- block elements in the periodic table and give the advantage of this kind of classification.

Ans: Depending upon the last coming electron enters in the atom of the given element, the elements are classified as ‘s’ ‘p’, ‘d’ and ‘f’ block elements.

s - block elements: 1. The differentiating electron enters into s - sub shell.

2. I A and II A groups of elements belong to s -block.

3. The general electronic configuration of these elements is ns1 to ns2.

p - block elements: 1. The differentiating electron enters into p - sub shell.

 2. III A to VIII A or zero groups of elements belong to p - block.

 3. The general electronic configuration of these elements is ns2 np1 to ns2 np6.

d-block elements: 1. The differentiating electron enters into d -sub shell.

2. IB to VIII B groups of elements belong to d - block. And all d - block elements are metals.

3. The general electronic configuration of these elements is ns2 np6 (n - 1)d1 to ns2 np6 (n - 1)d10.

f - block elements: 1. The differentiating electron enters into f -sub shell.

 2. The lanthanoids and actinoids below the periodic table are all f-block elements.

Advantages: 1. Division of elements into different block elements is useful to identify their physical and chemical properties easily.

 2. It is easy to choose substitute elements in the study of chemical reactions.