Modern Periodic Table solved examples, conceptual questions, and practice problems are essential for building a strong understanding of periodic classification and trends. This section helps students apply theoretical concepts like groups, periods, blocks, and electronic configuration to solve different types of questions. Regular practice improves problem-solving skills, accuracy, and confidence, making it highly useful for CBSE school board exams as well as competitive exams like JEE and NEET.
Solved Examples
What would be the IUPAC name and symbol of the element with atomic number 120?
Solution: The roots for 1, 2 and 0 are un, bi and nil respectively.
∴ Name of element : Unbinilium
Symbol : Ubn
How would you justify the presence of 18 elements in the 5th period of the periodic table?
Solution: The 5th period involves the filling of 5th shell (n=5). This period has 4d, 5s and 5p available orbitals. The total number of available orbitals are 9 and therefore the maximum number of electrons that can be accommodated is 18. Thus, 5th period contains 18 elements.
The elements Z = 107, 108 and Z = 109 have been made recently. Indicate the group in which you will place the above elements.
Solution: The electronic configurations of these elements are:
Z = 107 $[Rn] 5f^{14} 6d^5 7s^2$
Z = 108 $[Rn] 5f^{14} 6d^6 7s^2$
Z = 109 $[Rn] 5f^{14} 6d^7 7s^2$
These elements will be placed in d-block in groups 7th, 8th and 9th respectively.
Arrange the following elements in the increasing order of metallic character: Si, Be, Mg, Na, P.
Solution: We know that metallic character increases down a group and decreases along a period as we move from left to right.
Hence the order of increasing metallic character is P < Si < Be < Mg < Na.
Predict the position of the element in the periodic table satisfying the electronic configuration $(n-1)d^1 ns^2$ for n = 4
Solution: For n = 4, the electronic configuration is $3d^1 4s^2$. The element belongs to d-block elements.
Group number = No. of electrons in $(n-1)d$ subshell + No. of electrons in nth shell = 1 + 2 = 3
(a) Elements A, B, C and D have atomic numbers 12, 19, 29 and 36 respectively. On the basis of electronic configuration, write to which group of the periodic table each element belongs.
(b) Predict the blocks to which these elements can be classified. Also predict their periods and groups.
(c) Which of these are representative elements?
Solution: (a)
| Element | At. No. | Electronic configuration | Group |
|---|---|---|---|
| A | 12 | $1s^2 2s^2 2p^6 3s^2$ | 2 |
| B | 19 | $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$ | 1 |
| C | 29 | $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$ | 11 |
| D | 36 | $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6$ | 18 |
(b) Prediction of blocks
(i) A receives the last electron in 3s-subshell, therefore, it belongs to s-block.
Period = 3rd
Group = No. of valence electrons = 2
(ii) B receives the last electron in 4s-orbital, therefore, it belongs to s-block.
Period = 4th
Group = No. of valence electrons = 1
(iii) C receives the last electron in 3d-orbital, therefore, it belongs to d-block.
Period = 4th
Group = No. of electrons in ns and (n-1)d subshells = 11
(iv) D receives the last electron in the 4p-orbital, therefore, it belongs to p-block.
Period = 4th
Group = 10 + valence electrons = 10 + 8 = 18
(c) The elements A and B are representative elements.
Name the elements have the electronic configurations of some elements are given below:
(i) $1s^2 2s^2 2p^6 3s^1$
(ii) $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1$
(iii) $1s^2 2s^2 2p^3$
(iv) $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$
(v) $1s^2 2s^2 2p^6 3s^2 3p^5$
(vi) $1s^2 2s^2 2p^6 3s^2 3p^3$
(vii) $1s^2 2s^2 2p^6$
(viii) $1s^2 2s^2 2p^6 3s^2 3p^4$
Out of these which
1. is an alkaline earth metal
2. has lowest chemical reactivity
3. belong to group 15 of the periodic table
4. is a transition element
5. is halogen
6. belong to p-block
7. belong to second period.
Solution:
Names of elements:
(i) Sodium (Na) (ii) Scandium (Sc) (iii) Nitrogen (N) (iv) Calcium (Ca)
(v) Chlorine (Cl) (vi) Phosphorus (P) (vii) Neon (Ne) (viii) Sulphur (S).
- Calcium (iv) is an alkaline earth metal.
- Neon (vii) has lowest chemical reactivity.
- Nitrogen (iii) and phosphorus (vi) belong to group 15 of the periodic table.
- Scandium (ii) is a transition element.
- Chlorine (v) is halogen.
- Nitrogen (iii), chlorine (v), phosphorus (vi), neon (vii) and sulphur (viii) belong to p-block.
- Nitrogen (iii) and neon (vii) belong to second period of the periodic table.
Element A, B, C, D and E have the following electronic configurations:
A : $1s^2 2s^2 2p^1$
B : $1s^2 2s^2 2p^6 3s^2 3p^1$
C : $1s^2 2s^2 2p^6 3s^2 3p^3$
D : $1s^2 2s^2 2p^6 3s^2 3p^5$
E : $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$
Which among these will belong to the same group in the periodic table?
Solution: We know that the elements having similar valence electronic configuration belong to the same group of the periodic table. Therefore, elements A and B having three electrons in the valence shell belong to the same group i.e., group 13 of the periodic table.
Conceptual Questions and Answers
Q.1. On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements. [NCERT]
Ans. The sixth period of the periodic table begins with n=6. It involves the filling of 6s, 4f, 5d and 6p subshell in the increasing order of energy. The total number of orbitals available are 16 and therefore, the maximum number of electrons that can be accommodated is 32. Thus, the sixth period of the periodic table should have 32 elements.
Q.2. In terms of period and group where would you locate the element with Z = 114? [NCERT]
Ans. The electronic configuration of the element with Z=114 would be $[Rn] 5f^{14} 6d^{10} 7s^2 7p^2$. Since it has n=7 for the valence shell, it belongs to 7th period. It receives the last electron in p-orbital. Therefore, it belongs to p-block. The group number will be 10 + 4 (No. of electrons in ns and np orbitals) = 14. So, it belongs to 7th period and 14th group.
Q.3. The elements Z = 117 and 118 have been recently discovered and named. In which family group would you place these elements and also give electronic configuration in each case. Name these elements.
Ans. The electronic configuration of the element with Z = 117 would be $[Rn] 4f^{14} 5d^{10} 7s^2 7p^5$. It has outermost $ns^2 np^5$ configuration and therefore, it belongs to halogen family or Group 17.
IUPAC name: Tennessine, Ts
The electronic configuration of the element with Z=118 would be $[Rn] 4f^{14} 5d^{10} 7s^2 7p^6$. It has outermost $ns^2 np^6$ configuration and therefore, belongs to noble gases or group 18.
IUPAC name: Oganesson, Og.
Q.4. Write the atomic number of the element present in the third period and sixteenth group of the periodic table. Give its name.
Ans. Since it belongs to 3rd period, it will have outershell as n = 3. Its configuration would be $[Ne] 3s^2 3p^4$. So its atomic number = 16. It is sulphur.
Q.5. Give the general electronic configurations of
(i) p-block (ii) actinoids
Ans. (i) $ns^2 np^{1-6}$
(ii) $5f^{1-14} 6d^{0-2} 7s^2$
Q.6. An element ‘X’ with atomic number 112 has been recently predicted. Its electronic configuration is : $[Rn] 5f^{14} 6d^{10} 7s^2$. Predict
(i) group and (ii) block in which this element would be placed (iii) IUPAC name and symbol.
Ans. The configuration of the element is : $[Rn] 5f^{14} 6d^{10} 7s^2$
(i) It belongs to 12th group.
(ii) It belongs to d block.
(iii) IUPAC name is : Copernicium; Symbol : Cn.
Q.7. The element 119 has not been discovered so far. What would be the IUPAC name and the symbol for this element? On the basis of periodic table, predict the electronic configuration of this element and the formula of its most stable chloride and oxide. (NCERT Exemplar Problem)
Ans. IUPAC name : Ununennium Symbol : Uue
Electronic configuration : $1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 4f^{14} 5s^2 5p^6 5d^{10} 5f^{14} 6s^2 6p^6 6d^{10} 7s^2 7p^6 8s^1$ or $[At] 8s^1$
Formula : Chloride : ACl Oxide : $A_2O$
Q.8. Eka-aluminium and eka-silicon were named given by Mendeleev for the then unknown elements gallium and germanium respectively. A recently discovered element has first named as eka-mercury. What is its atomic number? Write its group number, electronic configuration, IUPAC name, official name and symbol.
Ans. The element which comes after mercury in the periodic table is eka-mercury. Its atomic number = 80 + 32 = 112
Electronic configuration: $[Rn] 5f^{14} 6d^{10} 7s^2$
IUPAC name : Uub
Official name: Copernicium, symbol : Cn
Q.9. Write the IUPAC names, official names and symbols for the elements having atomic numbers 108, 114 and 116.
Ans.
Z = 108 Unniloctium Uno ; Hassium Hs
Z = 114 Ununquadium Uuq ; Flerovium Fl
Z = 116 Ununhexium Uuh ; Livermorium Lv
Practice Problems
1. Write the name and deduce the atomic numbers of the following atoms:
(i) The third alkali metal.
(ii) Second transition element.
(iii) The fourth noble gas.
(iv) Fourth element in the second period.
2. The outer electronic configurations of some elements are:
(i) $3s^2 3p^4$
(ii) $3d^{10} 4s^2$
(iii) $3s^2 3p^6 4s^2$
(iv) $6s^2 4f^3$
State to which block in the periodic table each of these elements belong.
3. How many elements are present in the third period of the p-block elements?
4. Complete the following statements:
(a) There are…………………….periods in the long form of the periodic table.
(b) The s block element having highest atomic mass is ………………… .
(c) The elements Cu, Ag and Au are called ………………….. metals.
5. An element X belongs to the third period of the p-block elements. It has 4 electrons in the outermost shell. Name the element.
6. Which family of elements has the electronic configuration $ns^2 np^4$?
7. The element 118 has not yet been discovered. What is its IUPAC name and symbol?
8. Arrange the following elements in the increasing order of metallic character:
B, Al, Mg, K.
9. Arrange the following elements in the increasing order of non-metallic character:
B, C, Si, N and F.
10. Rn (Z = 86) is the last noble gas discovered. Predict what will be the atomic number of the next noble gas to be discovered. Write its symbol.
Answers to Practice Problems
- (i) K, 19 (ii) Ti, 22 (iii) Kr, 36 (iv) C, 6.
- (i) p (ii) d (iii) s (iv) f.
- Six.
- (a) 7 (b) Ra (c) Coinage.
- Silicon.
- Oxygen family. This family is also called chalcogens.
- Ununoctium, Uuo
- B < Al < Mg < K
- F < N < Si < C < B
- Atomic number of next noble gas to be discovered will be 118. Symbol : Uuo
Important Chapter Links
To master this topic, students should also study Modern Periodic Law and Modern Periodic Table (Groups, Periods, Blocks) and Division of Periodic Table into s, p, d, f Blocks. It is equally important to revise Structure of Atom for a clear understanding of electronic configuration. For better class 11 chemistry exam preparation, practice JEE Main and IMU CET Previous Year Questions (PYQs) and explore Class 11 Chemistry Complete Chapter Notes available on this website.