In the previous section, we saw how to determine the block name and period number of any element using the S.E.C. In this section we will see the method to determine the group number.
The rule for determining the group number of a given element will depend on the block in which that element resides. That means:
• The elements in the s-block have their own unique rule to determine group numbers
• The elements in the p-block have their own unique rule to determine group numbers
• The elements in the d-block have their own unique rule to determine group numbers
■ However there is basic step which is common for all blocks. It will be come clear when we write the rule for finding the group for any element.
Rule 9.3
Given any element. We want to know the group in which that element resides in the periodic table. For that, use the following steps:
■ Basic step for any element:
• Apply rule 9.1 and find the block in which the element resides in the periodic table
♦ Once we complete the above basic step, we can choose the appropriate one from A, B or C given below:
A. Rule for s-block
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the s subshell
3. In this s subshell, find the number of electrons
4. This number is the 'group number' of that element
B. Rule for p-block
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the s and p subshells
3. Find the total number of electrons in those s and p subshells
4. Add '10' to this sum
5. The final sum obtained by adding '10' is the 'group number' of that element
OR
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the p subshell
3. Find the number of electrons in that p subshell
4. Add '12' to this number
5. The sum obtained by adding '12' is the 'group number' of that element
C. Rule for d-block
1. From the S.E.C, find the outer most Main shell
• In the outer most main shell, find the s subshell
• Write down the number of electrons in this s subshell
2. From the S.E.C, find the second last Main shell
• In the second last main shell, find the d subshell
• Write down the number of electrons in this d subshell
3. Add the number of electrons in (1) and (2)
4. The sum thus obtained is the 'group number' of that element
Based on the above rules we can determine the group number of any given element. Consider the fig.9.2 that we saw in the previous section. For convenience, it is shown again below:
[Above fig.9.2 is taken from wikipedia. See details here]
■ We get the following information:
• Groups 1 and 2 belong to the s-block
• Groups 3 to 12 belong to the d-block
• Groups 13 to 18 belong to the f-block
■ We know that, the f-block elements consist of Lanthanides and Actinids.
• They are kept away from the main body of the periodic table. If we accommodate them, they will also get group numbers.
• But then, the periodic table will become very large. We saw those details in a previous chapter here.
Solved example 9.6
So we saw how to find the 'Group number' of any given element. We can now proceed to learn the properties of the elements of each block. In the next section, we will see the properties of s-block and p-block elements.
Arrangement of elements into Groups
The rule for determining the group number of a given element will depend on the block in which that element resides. That means:
• The elements in the s-block have their own unique rule to determine group numbers
• The elements in the p-block have their own unique rule to determine group numbers
• The elements in the d-block have their own unique rule to determine group numbers
■ However there is basic step which is common for all blocks. It will be come clear when we write the rule for finding the group for any element.
Rule 9.3
Given any element. We want to know the group in which that element resides in the periodic table. For that, use the following steps:
■ Basic step for any element:
• Apply rule 9.1 and find the block in which the element resides in the periodic table
♦ Once we complete the above basic step, we can choose the appropriate one from A, B or C given below:
A. Rule for s-block
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the s subshell
3. In this s subshell, find the number of electrons
4. This number is the 'group number' of that element
B. Rule for p-block
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the s and p subshells
3. Find the total number of electrons in those s and p subshells
4. Add '10' to this sum
5. The final sum obtained by adding '10' is the 'group number' of that element
OR
1. From the S.E.C, find the outer most Main shell
2. In the outer most main shell, find the p subshell
3. Find the number of electrons in that p subshell
4. Add '12' to this number
5. The sum obtained by adding '12' is the 'group number' of that element
C. Rule for d-block
1. From the S.E.C, find the outer most Main shell
• In the outer most main shell, find the s subshell
• Write down the number of electrons in this s subshell
2. From the S.E.C, find the second last Main shell
• In the second last main shell, find the d subshell
• Write down the number of electrons in this d subshell
3. Add the number of electrons in (1) and (2)
4. The sum thus obtained is the 'group number' of that element
 |
| Fig.9.2 |
■ We get the following information:
• Groups 1 and 2 belong to the s-block
• Groups 3 to 12 belong to the d-block
• Groups 13 to 18 belong to the f-block
■ We know that, the f-block elements consist of Lanthanides and Actinids.
• They are kept away from the main body of the periodic table. If we accommodate them, they will also get group numbers.
• But then, the periodic table will become very large. We saw those details in a previous chapter here.
Now we will see some solved examples
Solved example 9.3
The atomic number of an element is 16. Find the following:
(i) Subshell configuration (S.E.C) (ii) Block (iii) Period (iv) Group
Solution:
(i) 1s22s22p63s23p4 OR [Ne]3s23p4.
(ii) Block: Apply rule 9.1:
• The last electron is filled in the 3p subshell. So the element resides in the p-block
(iii) Period: Apply rule 9.2:
• The highest main shell number in the S.E.C is 3. So the element resides in the third period
(iv) Group: Apply rule 9.3 that we saw above.
We have already seen that the element belongs to the p-block. So apply Rule.9.3(B)
1. The outermost main shell is 3
2. The p subshell in this main shell is 3p
3. The number of electrons in this subshell is 4
4. Adding 12 to this number, we get: 4+12 = 16
5. So the group number is 16
Solved example 9.3
The atomic number of an element is 16. Find the following:
(i) Subshell configuration (S.E.C) (ii) Block (iii) Period (iv) Group
Solution:
(i) 1s22s22p63s23p4 OR [Ne]3s23p4.
(ii) Block: Apply rule 9.1:
• The last electron is filled in the 3p subshell. So the element resides in the p-block
(iii) Period: Apply rule 9.2:
• The highest main shell number in the S.E.C is 3. So the element resides in the third period
(iv) Group: Apply rule 9.3 that we saw above.
We have already seen that the element belongs to the p-block. So apply Rule.9.3(B)
1. The outermost main shell is 3
2. The p subshell in this main shell is 3p
3. The number of electrons in this subshell is 4
4. Adding 12 to this number, we get: 4+12 = 16
5. So the group number is 16
Solved example 9.4
(a) Which are the subshells in which electrons are filled in the s-block elements of the third period?
(b) Write the subshell electronic configuration (S.E.C) of the last element of this period
Solution:
Part (a):
1. We have two clues:
a. The elements belong to the s-block.
• So the last electron will be filled in the s subshell
b. The elements belong to the third period.
• So the highest 'main shell number' in the S.E.C will be 3
2. Combining the above two clues, we get:
• The last term in the S.E.C is 3s
3. If the last term is 3s, the following subshells would be already filled:
1s, 2s, and 2p
4. So the subshells present are:
1s, 2s, 2p and 3s
Part (b)
1. The clue is:
• The element is the last one of the third period
2. So we can write:
• The element belongs to the last group 18.
• So it belongs to the p-block
• So the last electron will be filled in the 3p subshell
3. Now we take Rule 9.3 (B)
• The group number is 18. It is obtained by adding 12 to the number of electrons in the 3p subshell.
• Thus, the number of electrons in the 3p subshell is 18-12 = 6
4. So the last term in the S.EC is 3p6.
• So the terms before that are: 1s2,2s2, 2p6 , and 3s2
• Thus the S.E.C is: 1s22s22p63s23p6.
Solved example 9.5
(a) Which are the subshells in which electrons are filled in the s-block elements of the third period?
(b) Write the subshell electronic configuration (S.E.C) of the last element of this period
Solution:
Part (a):
1. We have two clues:
a. The elements belong to the s-block.
• So the last electron will be filled in the s subshell
b. The elements belong to the third period.
• So the highest 'main shell number' in the S.E.C will be 3
2. Combining the above two clues, we get:
• The last term in the S.E.C is 3s
3. If the last term is 3s, the following subshells would be already filled:
1s, 2s, and 2p
4. So the subshells present are:
1s, 2s, 2p and 3s
Part (b)
1. The clue is:
• The element is the last one of the third period
2. So we can write:
• The element belongs to the last group 18.
• So it belongs to the p-block
• So the last electron will be filled in the 3p subshell
3. Now we take Rule 9.3 (B)
• The group number is 18. It is obtained by adding 12 to the number of electrons in the 3p subshell.
• Thus, the number of electrons in the 3p subshell is 18-12 = 6
4. So the last term in the S.EC is 3p6.
• So the terms before that are: 1s2,2s2, 2p6 , and 3s2
• Thus the S.E.C is: 1s22s22p63s23p6.
Solved example 9.5
When the last electron of an atom was filled in the 3d subshell, the S.E.C was recorded as 3d8. Answer the following questions related to this atom
(i) Write the complete S.E.C
(ii) What is the atomic number, block name, period number and group number of this atom?
Solution:
1. When the last electron is filled, 3d8 is obtained.
2. The filling of 3d can begin only after completely filling up 4s
3. That means 4s is completely filled up. This gives us 4s2.
4. If 4s is completely filled, all the subshells preceding it should be already filled up. Let us write those preceding subshells in order:
1s, 2s, 2p, 3s and 3p
5. The above subshells are completely filled up. So the S.E.C is:
1s22s22p63s23p64s23d8 OR [Ar]4s23d8
Solution:
1. When the last electron is filled, 3d8 is obtained.
2. The filling of 3d can begin only after completely filling up 4s
3. That means 4s is completely filled up. This gives us 4s2.
4. If 4s is completely filled, all the subshells preceding it should be already filled up. Let us write those preceding subshells in order:
1s, 2s, 2p, 3s and 3p
5. The above subshells are completely filled up. So the S.E.C is:
1s22s22p63s23p64s23d8 OR [Ar]4s23d8
Solved example 9.6
The S.E.C of 5 elements are given below. Pick out the wrong ones from among them
(i) 1s22s22p7 (ii)1s22s22p2 (iii)1s22s22p53s1 (iv)1s22s22p63s23p64s13d2 (v)1s22s22p63s23p64s23d2
Solution:
■ (i), (iii) and (iv) are wrong.
Explanation:
• Consider (i) 1s22s22p7: The p subshell can carry a maximum of 6 electrons only
• Consider (iii)1s22s22p53s1: The 3s can begin only after completely filling the 2p with 6 electrons
• Consider (iv)1s22s22p63s23p64s13d2: The 3d can begin only after completely filling the 4s with 2 electrons
(i) 1s22s22p7 (ii)1s22s22p2 (iii)1s22s22p53s1 (iv)1s22s22p63s23p64s13d2 (v)1s22s22p63s23p64s23d2
Solution:
■ (i), (iii) and (iv) are wrong.
Explanation:
• Consider (i) 1s22s22p7: The p subshell can carry a maximum of 6 electrons only
• Consider (iii)1s22s22p53s1: The 3s can begin only after completely filling the 2p with 6 electrons
• Consider (iv)1s22s22p63s23p64s13d2: The 3d can begin only after completely filling the 4s with 2 electrons
So we saw how to find the 'Group number' of any given element. We can now proceed to learn the properties of the elements of each block. In the next section, we will see the properties of s-block and p-block elements.
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