Important Questions

1. (a) Give reason whether the following group is a Dobereiner's traid or not. Na, Si, Cl (Atomic weights of Na, Si, Cl are 23, 28, 35.5 respectively)
(b) What is the atomic weight of Se? If S, Se, Te are Dobereiner's traid
(Atomic weight of S and Te are 32, 125)                                                                      (AS 1) 4 Marks
A: a) Na(23), Si(28), Cl(35.5). It is not a Doberiner's traid because the atomic weight of middle element (Si (28)) is not equal to the average of atomic weights of Na(23) and Cl(35.5).

2. Define the Mendeleev's periodic law. Explain the salient feature and achievements of the Mendeleev's periodic table?                                                                               (AS 1) 4 Marks
A: Mendeleev's periodic law:
"The law states that the physical and chemical properties of the elements are a periodic function of their atomic weights".

Salient features and achievements of the Mendeleev's periodic table:
1. Groups and Sub - groups:
There are eight vertical columns called groups represented by Roman numerals I to VIII. Each group is divided into two Sub - groups A and B. The elements present in a group and its Sub - group have similar properties.
2. Periods:
The Horizontal rows in Mendeleev's table are called periods. There are seven periods in the table. Which are denoted by Arabic numeral 1 to 7. A period comprises the entire range of elements after which properties repeat themselves.
3. Predicting the properties of missing elements:
Based on the arrangement of the elements in the table. He predicted that some elements were missing and left blank spaces at the appropriate places in the table. He named those elements tentatively by adding the prefix eka to the name of the element immediately above the each empty space.
e.g.: Eka - boron, Eka - aluminium, Eka - Sillion were close to the observed properties of Scandium, Gallium and Germanium respectively which were discovered later.

4. Correction of atomic weight:
The correct placement of elements in Mendeleev's periodic table helped in correction the atomic masses of some elements like Beryllium, Indium, Gold.
5. Anomalous Series:
Some anomalous series of elements like 'Te' and 'I' were observed in the table. The anomalous series contained elements with more atomic weight like (Te) placed before the element with less atomic weight like I.

3. What are the salient features of Modern periodic table?
                                                                                    or
Explain the features of long form of periodic table based on the law "The physical and chemical properties of elements are the periodic function of the electronic configuration of their atoms" mention its special features.    (AS 1) 4 Marks
A: Modern periodic law:
The properties of the elements are periodic function of their atomic numbers construction of the long form periodic  table.

Special features of modern periodic table:
‣ The modern periodic table has eighteen vertical columns known as groups and seven horizontal rows known as periods.
‣  The elements with similar outer shell (valence shell) electronic configurations in their atoms are in the same column called group. They are represented by using Roman numeral I through VIII with letters A and B traditional notation. According to latest recommendation of the IUPAC. These groups are represented by Arabic numerals 1 through 18.
‣ Depending upon to which sub - shell that 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.
‣  The number of elements in period depend on how electrons are filled into various shells. Each period starts with a new shell and ends when shell is completely filled.
‣  The first period starts with K - shell which contains only one sub shell 1s. So first period has only two elements (H, He).
‣  Second period starts with the second main shell (L) which contains two sub - shells (2s, 2p). Eight types of configurations are possible in this shell (L) like 2s¹ and 2s² and 2p¹ to 2p⁶. Hence the second period contains elements Li, Be, B, C, N, O, F and Ne in the order given thus, the 2^nd period consists two s - block elements (Li, Be) and six p - block elements (B to Ne).
‣  Third period starts with third main shell (M). This shell (M) has 3 sub - shells namely 3s, 3p and 3d but while electrons are being filled into the shell '3d' gets electrons only after '4s' is filled. Therefore, the 3^rd period containing again 8 elements, which includes two s - block elements (Na, Mg) and six p - block elements (Al to Ar).
‣  Fourth main shell (N) has four sub-shells (4s, 4p, 4d, 4f) but the electrons enter the atoms in the order 4s, 3d and 4p. So, 18 elements can be filled in this period.
‣  On the same lives, 18 elements are in the 5^th period.
‣  7th period is in complete and contains 2 elements from s - block (7s), 14 elements from f - block (5f), 10 elements from d - block (6d) and some elements from p - block (7p).
‣  The 4f elements are called lanthanides and 5f elements are called actinides, which are separately place at the bottom of the periodic table.

4. How do atomic radius, Inoization energy, Electron affinity, Electronegativity, Metallic and Non - metallic properties. Vary in a period and in a group?                                        (AS 1) 4 Marks
A: a) Atomic radius:
In periods: Atomic radius decreases from left to right in a period.
In groups: Atomic radius increase from top to bottom in a group.
b) Ionization energy:
In periods: Ionization energy does not follow a regular trend but totally increases due to increase in atomic number. When we move from left to right in a period.
In groups: Ionization energy decreases due to increase in atomic size when we move from top to bottom in a group.
c) Electron affinity:
In periods: Electron affinity values increases from left to right in a period.
In groups: Electron affinity decreases from top to bottom in a group.
d) Electronegativity:
In periods: Electronegativity increases from left to right in a period.
In groups: Electronegativity values decreases from top to bottom in a group.
e) Metallic and non - metallic properties:
In periods: Metallic character decreases, while non - metallic character increases as we move along a period from left
to right.
In groups: Metallic character increases, while non - metallic character decreases in a group as we move from top to bottom.

5. Mention and Explain the factors of influencing Ionization energy.
                                                                           OR
Explain different factors which influence the Ionization energy.                              (AS 1) 4 Marks
A: Factors effect the Ionization energy:
i) Nuclear charge: More the nuclear charge more is the ionization energy.
e.g.: Between 11Na and 17Cl, Chlorine atom has more ionization energy.
ii) Screening effect or shielding effect:
More the shells with electrons between the nucleus and the valence shell, they act as screens and decrease nuclear attraction over valence electron. This is called the screening effect. More the screening effect, less is the ionization energy.
e.g.: Between ₃Li and ₅₅Cs, the element ₅₅Cs with more inner shells has less ionization energy.
iii) Penetration power of the orbitals:
Orbitals belonging to the same main shell have different piercing power towards the nucleus, for example 4s > 4p > 4d > 4f in the penetration. Therefore, it is easier to remove 4f electron than 4s.
iv) Stable configuration: It is easier to remove one electron from ₈O (1s² 2s² 2p⁴) than 7N (1s² 2s² 2p³). This is because, ₇N has stable half filled configuration.
v) Atomic radius: More the atomic radius, less is the ionization energy. Therefore, ionization energy of 'F' is greater than that of 'I'.

6. The figure given below shows a part of periodic table. Five elements in first three periods are shown by P, Q, R, S, T which are not the original symbols of those elements.
                                                                                                                                  18

i) Which letters represent alkalimetals?
A: S
ii) Write the letter which represents a noble gas?
A: R
iii) What is the letter that shows Halogen?
A: T
iv) Which type of bond will be formed between the elements P and T?
A: Covalent bond

7. Atomic sizes of few elements of 2nd period are given in the table observe the table and answer the questions given below.                                                                                            (AS 4) 4 Marks

i) Arrange the elements in increasing order of their atomic sizes.
A: F, O, N, C, B, Be, Li
ii) Which is the element nearest to the electronic configuration of a noble gas in II period.
A: Li, F
iii) Which is the outermost orbit of all these elements?
A: L-shell
iv) Whose atomic size among Be and C is more?
A: Be

8. Observe the table and answer the questions.                                                  (AS 4) 4 Marks
 

i) Which elements atom has less atomic size?
A: Cl
ii) Write the electronic configurations of Al and Cl.
A: Al: 1s² 2s² 2p⁶ 3s² 3p¹
Cl: 1s² 2s² 2p⁶ 3s² 3p⁵
iii) Find the elements whose physical and chemical properties are same as of K.
A: Na, Rb
iv) Which is the element with more atomic radius?
A: Rb.

9. Electro negativity values of certain elements belonging to VIIA (17^th group) and 2nd period are given in the above table observe them and answer the questions given below.       (AS 4) 4 Marks
i) Arrange the elements of 17th group in the increasing order of their electro negativities.
A: I(2.5), Br(2.8), Cl(3.0), F(4.0)
ii) Which is the element with highest electronegativity value?
A: F(4.0)
iii) Name the element of lowest electronegativity.
A: Li(1.0)
iv) How do the values of electronegativity values vary in a group and in a period?
A: Electronegativity increases from left to right in a period. Electronegativity values decreases from top to bottom in a group.

10. The electron affinity values of elements of VIIA and VIA groups are given in the table with the help of table answer the questions given below the table. (AS 4) 4 Marks

i) What are the units of electron affinity?
A: kJ/mole.
ii) Arrange the elements of chalcogen group as per the decreasing order of their electron affinity values.
A: O(-141), Po(-174), Te(-190), Ge(-195), S(-200)
iii) How do the electron affinity values vary in a group and in a period?
A: Electron affinity values increases from left to right in a period. Electron affinity decreases from top to bottom in a group.
iv) What happens to the energy value when electron affinity values will be either positive or negative?
A: Negative sign for energy value in table indicates that energy is liberated or lost, and the positive sign tells that the energy is gained or absorbed.

11.

                                                                                                                           (AS 1) (AS 4) 4 Marks
i) If in 2^nd and 3^rd periods from left to right what will be the change in Atomic Size? Support your answer.
A: The Atomic size when we go from left to right in the table decreases. It is because that in a period when we go from left to right atomic number increases. The incoming electron enters into the same shell, the nuclear attraction increases on outermost orbital electrons. Hence atomic size decreases.
ii) In a period from left to right, how does the metallic character of elements vary?
A: When we go from left to right in the above table the metallic character decreases and non - metallic character of element increases. In period the first two or three metals are as metals. Next one or two elements are like semi metals and the last three elements are like non - metals. Due to this metallic character decreases and non-metallic character increases in period.

12. Certain electronic configurations are given below.                                    (AS 4) 4 Marks

i) Find out the wrong electronic configuration.
 
ii) Write the name of the element whose configuration is wrong and correct it.

iii) Find out the electronic configuration of Chromium and to which period this belongs to?


13. Write down the characteristics of the elements having atomic number 12.
                                                                                                                                              (AS 1) 2 Marks
a) Period number b) Group number c) Valency d) Element family
A: a) Period number - 3 b) Group number - IIA
c) Valency - 2  d) Element family - Alkali earth metal family

14. Observe the electronic configurations given below and write the group and period numbers of those elements.                                                                                                                  (AS 1) 2 Marks

A: a) Group number - VIA
Period Number - 2
b) Group Number - IVA
Period Number - 3

15. The electronic configuration of the elements X, Y and Z are given below. (AS 1) 2 Marks

a) Which element belongs to third period?
A: Y belongs to third period.

b) Which element belongs to VIIIA group?
A: Z belongs to VIIIA group.

16. State whether the following elements belong to a group (G), period (P) or neither group nor period (N).                                                                                                                           (AS 1) 2 Marks

A:   

ii) That means, the elements having the similar valency electronic configuration have similar properties.
iii) But the valency electronic configuration of different elements in the same period is different. So, the properties of different elements in a period are different.

18. Mention the factors effecting electronic affinity.                                                    (AS 1 ) 2 Marks
A: The factors that effecting electronic affinity:
i) Nuclear charge
ii) Screening effect or shielding effect
iii) Penetration power of the orbitals
iv) Stable configuration
v) Atomic radius

19. Complete the table                                                                                                       (AS 4) 2 Marks

A.

20. Observe the electronic configurations of few elements is given and identify to which block the element belong to?                                                                                                            (AS 1) 2 Marks


21. Fill the following table with suitable answers.                                                          (AS 4) 2 Marks

A:
 

22. Fill the following table with suitable answer.                                                           (AS 4) 2 Marks

A:

23. 

i) Which element belongs to 17^th group?
ii) Write the symbol of element that belongs to 15^th group.                                         (AS 1) 2 Marks
A: Atomic number of 'X' is 5. Its configuration is 2, 3.
Atomic number of 'Y' is 7. Its configurations is 2, 5.
Atomic number 'Z' is 9. Its configuration is 2, 7.
i) Element 'Z' belongs to group 17. It is Fluorine (F).
ii) Element 'Y' belongs to group 15. It is Nitrogen (N).

24. Which one between Cl and Cl^- would have more size? Why?                                (AS 1) 2 Marks
A: i) The electronic configuration of chlorine is 1s² 2s² 2p⁶ 3s² 3p⁵
ii) The electronic configuration of chloride (Cl^-) ion is 1s² 2s² 2p⁶ 3s² 3p⁶.
iii) Both Chlorine and chloride ions have 17 protons each but there are 17 electrons in Chlorine atom, where as 18 electrons in Chloride ion.
iv) Therefore the nuclear attraction is less in Cl^- ion when compared with Chlorine atom. Therefore the size of the Chlorine (Cl) atom is less than Cl^- ion.

25. How are the elements divided into s, p, d and f - blocks in the modern periodic table?                                                                                                                                   (AS 1) 2 Marks
A: Depending upon to which sub - shells 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.
e.g.: i) ₁₁Na
            The electronic configuration of Na is 1s² 2s² 2p⁶ 3s¹
            The differentiating electron gets into 3s level. Therefore 11Na belongs to s - block
ii) Similarly ₁₃Al (1s² 2s² 2p⁶ 3s² 3p¹) belongs to p - block
iii) ₂₁Sc (1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹) belongs to d - block
iv) 58Ce (1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s² 5d⁰ 4f²) belongs to f - block

26. On What basis did Mendeleev arrange the elements in his periodic table?      (AS 1) 1 Mark
A: Atomic Masses.

27. In the modern periodic table. Which are the metals among the first ten elements?   (AS 1) 1 Mark
A: Lithium, Beryllium.

28. On which side of the periodic table will you find metals?                                (AS1) 1 Mark
A: Left side.

29. On which side of the periodic table will you find non-metals?                       (AS 1) 1 Mark
A: Right Side.

30. Name two elements with completely filled outermost shell?                         (AS 1) 1 Mark
A: Helium, Neon.

31. Name two elements that have a single electron in their outermost shell?       (AS 1) 1 Mark
A: Hydrogen, Lithium.

32. Which element has two shells, both of which are completely filled with electrons.  (AS 1) 1 Mark
A: Neon (2, 8)

33. What is the similarity in the electronic configuration of Li, Na and K?        (AS 1) 1 Mark
A: All the elements are in group 1 (IA) and have one electron in their valence shell.

34. What is the name of those elements which divide metals and non - metals in the periodic table.                                                                                                                                       (AS 1) 1 Mark
A: Metalloids.

35. Arrange the following elements in the increasing order of their metallic character Na, K, Mg, Al                                                                                                                                              (AS 1) 1 Mark
A: Al < Mg < Na < K.

Short Questions
1. Ca, Sr, Ba are Dobereiner's triads, Atomic weights of Ca and Ba are 40.0 and 137.0, then what is the Atomic weight of Strantium? (AS1) 1 Mark


2. Write any two limitations of Dobereiner's theory. (AS1) 1 Mark
A: 1) All the known elements at that time could not be arranged in the form of triads.
     2) The law failed for very low mass or for very high mass elements.

3. Which law explains the following statement. "When the elements are arranged in the ascending order of their atomic weights, they fall into a pattern in which their properties repeat at regular intervals"? (AS1) 1 Mark
A: Newlands law of octaves.

4. Write any two limitations of Newlands octaves theory. (AS1) 1 Mark
A: 1) Newland's octave law can fit only 56 elements.
      2) Certain elements, totally dissimilar in their properties were fitted into the same group.

5. How many groups and periods present in Mendeleev's periodic table? (AS1) 1 Mark
A: 8 groups and 7 periods.

6. What are the new elements discovered in place of Eka Boron, Eka Aluminium and Eka silicon? (AS1) 1 Mark
A: Scandium, Gallium, and Germanium are discovered in place of Eka Boron, Eka Aluminium and Eka Silicon respectively.

7. On which statement modern periodic table is constructed? (AS1) 1 Mark
A: The physical and chemical properties of the elements are the periodic functions of their electronic configurations.

8. How the modern periodic table is classified into s, p, d, f blocks? (AS1)1 Mark
A: Depending upon to which sub - shell the differentiating (or) last coming electron enters in the atom of a given element, the elements are classified into s, p, d, f block elements.

9. Scandium belongs to which block element? (AS1) 1 Mark
A: d - block element (Sc - electronic configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹)

10. Alkali earth metals belongs to which group? (AS1) 1 Mark
A: II A - group

11. VI - A (16) group elements belongs to which family? (AS1) 1 Mark
A: Chalcogen family.

12. Write valency shell electronic configuration of I A - group elements? (AS1) 1 Mark
A: ns¹.

13. What is the valency of carbon family? (AS1) 1 Mark
A: 4.

14. How many valency electrons are present in Boron family. (AS1) 1 Mark
A: 3(ns²np¹)

15. How many elements are present in 6^th period of long form of periodic table? (AS1) 1 Mark
A: 32

16. What is the valency of Calcium elements? (AS1) 1 Mark
A: 2

17. Write the change in non - metallic and metallic properties of a group? (AS1) 1 Mark
A: In a group from top to bottom non metallic character gradually decreases and metallic property gradually
increases.

18. Which of the block in a periodic table have non - metals, metals and metalloids? (AS1) 1 Mark
A: p - block

19. In Periodic table, which of the group has Lanthanides and Actinides? (AS1) 1 Mark
A: 3 (III B)

20. In a period, which group element has more atomic radius? (AS1) 1 Mark
A: 1 (I A) Group.

21. Which element in the periodic table has highest atomic radius? (AS1) 1 Mark
A: Cesium (Cs)

22. Which of the element in periodic table has smaller size? (AS1) 1 Mark
A: Helium (He)

23. Among Na⁺, Mg²⁺ and Al³⁺, write increasing order of ionic radii. (AS1) 1 Mark
A: Al³⁺ < Mg²⁺ < Na⁺

24. Among Na, Mg²⁺ which will have less radius? (AS1) 1 Mark
A: Mg²⁺

25. Among Cl and Cl ^-, which will have larger size? (AS1) 1 Mark
A: Cl ^- has larger size.

26. What is the tendency of Ionization potential in a group? (AS1) 1 Mark
A: In a group from top to bottom I.P. values gradually decreases.

27. What is the tendency of Electron affinity along the period? (AS1) 1 Mark
A: In a period, from left to right Electron affinity values gradually increases.

28. Which of the element in periodic table has highest Ionization Energy? (AS1) 1 Mark
A: Helium.

29. Which group elements of periodic table has highest Electronegativity values? (AS1) 1 Mark
A: Halogens - VII A Group.

30. The element having atomic number 21, belongs to which group and which period in a periodic table. Imagine? (AS2) 1 Mark
A: Atomic number - 21 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹. This element belongs to 4^th period and present in 3 (IIIB) group.