Have you ever wondered why elements in the same group show similar chemical properties or why the properties of elements change regularly across a period? How does the arrangement of electrons in different shells and subshells influence an element's position in the periodic table? Understanding electronic configuration in periods and groups helps explain the periodic trends and the classification of elements based on their atomic structure.
This Story also Contains
Period in the Modern Periodic Table
Block in the Modern Periodic Table
Some Solved Examples
Electronic configuration in Periods and Groups
This topic falls under the broader subject of "Classification of Elements and the Periodic Table," a fundamental chapter in Class 11 Chemistry. It is crucial not only for board examinations but also for competitive entrance exams such as JEE Main, NEET, SRMJEE, BITSAT, WBJEE, BCECE, and others.
Period in the Modern Periodic Table
A period is a horizontal row in the Modern Periodic Table. There are seven periods in the periodic table, numbered from 1 to 7. Elements belonging to the same period have the same number of electron shells in their atoms. As we move from left to right across a period, the atomic number increases by one unit, and electrons are added to the same outer shell. Consequently, the properties of elements change gradually across a period. The period number of an element corresponds to the highest principal energy level (shell) occupied by electrons in its atom.
Block in the Modern Periodic Table
The block of an element in the Modern Periodic Table is determined by the subshell into which its last electron enters. Based on the electronic configuration of elements, the periodic table is divided into four blocks: s-block, p-block, d-block, and f-block. Elements within the same block have similar valence shell electronic configurations and often exhibit similar chemical properties.
Types of Blocks
s-Block Elements
The last electron enters the s-subshell.
Includes Groups 1 and 2, along with hydrogen and helium.
This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.
There are only two series of f-block, i.e., lanthanide and actinide. If the last electron of any element enters into the f-subshell and if the atomic number is between 57-71, then the element belongs to the lanthanide series, i.e., 6th period. Further, if the last electron of any element enters into the f-subshell and if the atomic number is between 89-103, then the element belongs to the actinide series, i.e., 7th period. All the elements from both these series belong to group 3.
1) The period of the element is determined by its highest shell
2) The period of the element is determined by its last orbital
3) The period of the element is determined by its valence shell electrons
4) The period of the element is determined by its valency
Solution: The period of the element is determined by its highest shell.
Hence, the answer is option (1).
Question 2: An element with atomic number 23 belongs to which period?
1) 3rd period
2) 2nd period
3) 5th period
4) 4th period
Solution: We have to check the last shell. The shell with a higher value of the principal quantum number(n) is the period for that element. The electronic configuration of an element having atomic number 23, is = [Ar] 3d3 4s2. The shell has a higher value of n is 4s. Therefore the period is = 4.
Hence, the answer is option (4).
Question 3: K has an atomic number 19, thus its electronic configuration can be written as:
1s22s22p63s23p64s1
Now it has 1 electron in the s-subshell, therefore K belongs to Group 1.
Question 4: Ge has an atomic number 32, thus its electronic configuration can be written as:
1s22s22p63s23p64s23d104p2
Now, it has 2 electrons in the last p-subshell, therefore its group number is:
12 + 2 = 14
Thus, Ge belongs to Group 14
Question 5: Mn has the atomic number 25, thus its electronic configuration can be written as:
1s22s22p63s23p64s23d5
Now it has 5 electrons in the d-subshell, therefore its group number is:
2 + 5 = 7
Thus, Mn belongs to Group 7.
Question 6: The element with atomic number 35 belongs to which group:
1) 13th group
2) 17th group
3) 16th group
4)2nd group
Solution: The electronic configuration of the element with atomic number 35 is:
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Now, the group of the element is determined by the following formulae:
(i) For s-block: ns1 and ns2
(ii) For p-block: 12 + number of electrons in the P-subshell of the last shell.
=12 + 5 =17th group
(iii) For d-block: 2 + number of electrons in (n-1)d subshell.
Hence, the answer is the option (2).
Practice more Questions from the link given below:
The numbers 2, 8, 8, 18, 18, 32 describe the typical increase in total electron count when moving down a group, not the absolute capacity of each shell. Each jump corresponds to filling subshells in this sequence: s, p, d, f.
Essentially, electrons add in these increments (+2, +8, +8, +18, +18, +32) due to the Aufbau principle, which fills subshells in order of increasing energy (n + ℓ rule).
So reading down a column: you go from one element to the next by adding roughly these numbers of electrons in order, reflecting how shells and subshells actually fill in real atoms.
Q: What is 7th period of periodic table?
A:
It spans 32 radioactive elements from Francium (Fr, Z=87) to Oganesson (Og, Z=118), covering the s-, f-, d-, and p-blocks.
All elements are radioactive, with many being synthetic and extremely short-lived.
The period was completed in 2016 with the official recognition of superheavy elements Nihonium, Moscovium, Tennessine, and Oganesson
Q: What is 2 8 8 18 18 32 rule?
A:
The numbers 2, 8, 8, 18, 18, 32 describe the typical increase in total electron count when moving down a group, not the absolute capacity of each shell. Each jump corresponds to filling subshells in this sequence: s, p, d, f.
Essentially, electrons add in these increments (+2, +8, +8, +18, +18, +32) due to the Aufbau principle, which fills subshells in order of increasing energy (n + ℓ rule).
So reading down a column: you go from one element to the next by adding roughly these numbers of electrons in order, reflecting how shells and subshells actually fill in real atoms.
Q: What is 7th period of periodic table?
A:
It spans 32 radioactive elements from Francium (Fr, Z=87) to Oganesson (Og, Z=118), covering the s-, f-, d-, and p-blocks.
All elements are radioactive, with many being synthetic and extremely short-lived.
The period was completed in 2016 with the official recognition of superheavy elements Nihonium, Moscovium, Tennessine, and Oganesson
Q: Why do elements in the same group behave similarly?
A:
They share the same number of valence electrons, resulting in matching outer-shell electron configurations—hence similar chemistry.
Q: Why do periods contain different numbers of elements?
A:
because each shell and subshell holds a specific maximum:
Shell n can hold up to 2n² electrons (e.g. n=2 → 8 electrons: 2s+2p)
Q: Why do elements in the same group behave similarly?
A:
They share the same number of valence electrons, resulting in matching outer-shell electron configurations—hence similar chemistry.
Q: What is electronic configuration?
A:
Electronic configuration is the arrangement of electrons in an atom's orbitals. It describes how electrons are distributed in different energy levels and sublevels around the nucleus, following specific rules based on quantum mechanics.
Q: How does the period number relate to electron configuration?
A:
The period number equals the principal quantum number (n) of the outermost shell.
Period 1 has n = 1 (fills 1s).
Period 2 has n = 2 (fills 2s and 2p), and so on .
Q: Why do periods contain different numbers of elements?
A:
because each shell and subshell holds a specific maximum:
Shell n can hold up to 2n² electrons (e.g. n=2 → 8 electrons: 2s+2p)
