In the previous section, we saw the electronic configuration of elements upto the thirtieth element. That is., up to zinc. In this section we will see some solved examples. Later we will also see some applications of writing the electronic configuration using subshells.
Solved example 9.1
In the main shell 4, Which subshell has the least energy and which subshell has the maximum energy?
Solution:
1. In the main shell 4, there will be 4 subshells. The 4 subshells in general are s, p, d and f.
2. In the main shell 4, they are written as 4s, 4p, 4d and 4f. We are asked which of these four has the least and maximum energies
3. Consider fig.9.1(c). For convenience, it is shown again below:
4. We follow the path shown by the arrow. Among the four subshells 4s, 4p, 4d and 4f, the first one to reach is 4s. So it has the least energy among the four.
5. The last one to reach is 4f. So it has the maximum energy among the four
■ This is also clear from the graphical representation given here. Among the four subshells, 4s occupies the bottom most position and 4f occupies the top most position.
Solved example 9.2
The subshell wise electronic configuration (S.E.C) of an atom is 1s22s22p63s2. Find the answers to the following:
(i) How many shells are present in this atom?
(ii) Which are the subshells of each shells?
(iii) What is the total number of electrons in the atom?
(iv) What is it's atomic number?
(v) How can this subshell electronic configuration be written in a short form?
Solution:
(i) We have S.E.C as 1s22s22p63s2.
• The numbers just before the subshell names give us the names of the main shells (main shells are some times simply called as 'shells')
• In the given S.E.C, the maximum number is '3'
• So it means that shells upto 3 (which is same as M) are present in the atom
• If M is present, K and L will also be present. So 3 shells are present in the atom
(ii) In the shell 1, the s subshell is present
• In shell 2, s and p subshells are present
• In shell 3, s subshell is present
(iii) Total number of electrons is the sum of all superscripts
This is equal to 2 + 2 + 6 + 2 = 12
(iv) The number of electrons = number of protons = 12
• So atomic number = 12
(v) The given S.E.C is 1s22s22p63s2.
• Detach the last 3s2. We get: 1s22s22p6.
• This is the S.E.C of Neon (Ne)
• So the short form is: [Ne]3s2.
So we saw how to find the 'Block name' and 'Period number' from the S.E.C. In the next section, we will see how to find the 'Group number' from the S.E.C.
Solved example 9.1
In the main shell 4, Which subshell has the least energy and which subshell has the maximum energy?
Solution:
1. In the main shell 4, there will be 4 subshells. The 4 subshells in general are s, p, d and f.
2. In the main shell 4, they are written as 4s, 4p, 4d and 4f. We are asked which of these four has the least and maximum energies
3. Consider fig.9.1(c). For convenience, it is shown again below:
5. The last one to reach is 4f. So it has the maximum energy among the four
■ This is also clear from the graphical representation given here. Among the four subshells, 4s occupies the bottom most position and 4f occupies the top most position.
Solved example 9.2
The subshell wise electronic configuration (S.E.C) of an atom is 1s22s22p63s2. Find the answers to the following:
(i) How many shells are present in this atom?
(ii) Which are the subshells of each shells?
(iii) What is the total number of electrons in the atom?
(iv) What is it's atomic number?
(v) How can this subshell electronic configuration be written in a short form?
Solution:
(i) We have S.E.C as 1s22s22p63s2.
• The numbers just before the subshell names give us the names of the main shells (main shells are some times simply called as 'shells')
• In the given S.E.C, the maximum number is '3'
• So it means that shells upto 3 (which is same as M) are present in the atom
• If M is present, K and L will also be present. So 3 shells are present in the atom
(ii) In the shell 1, the s subshell is present
• In shell 2, s and p subshells are present
• In shell 3, s subshell is present
(iii) Total number of electrons is the sum of all superscripts
This is equal to 2 + 2 + 6 + 2 = 12
(iv) The number of electrons = number of protons = 12
• So atomic number = 12
(v) The given S.E.C is 1s22s22p63s2.
• Detach the last 3s2. We get: 1s22s22p6.
• This is the S.E.C of Neon (Ne)
• So the short form is: [Ne]3s2.
Now we will see some of the applications of subshell wise electronic configuration (S.E.C) of elements.
[Above fig.9.2 is taken from wikipedia. See details here]
• We want to know the basis of such a classification. Let us analyse:
Following are some elements taken at random from the periodic table. Some details are also written about them:
■ Element: 3Li
1. Atomic number: 3
2. S.E.C: 1s22s1
3. Subshell to which the last electron is added: s
4. Block: s-block
■ Element: 12Mg
1. Atomic number: 12
2. S.E.C: 1s22s22p63s2
3. Subshell to which the last electron is added: s
4. Block: s-block
■ Element: 7N
1. Atomic number: 7
2. S.E.C: 1s22s22p3
3. Subshell to which the last electron is added: p
4. Block: p-block
■ Element: 21Sc
1. Atomic number: 21
2. S.E.C: 1s22s22p63s23p64s23d1
3. Subshell to which the last electron is added: d
4. Block: d-block
♦ Subshell to which the last electron is added
♦ The block in which the element resides in the periodic table.
• As these two items are same for every element, we can write it as a rule. This rule can be written in steps.
Rule 9.1:
■ Given any element. We want to know the block in which that element resides in the periodic table. For that, use the following steps:
1. Write the S.E.C.
2. Find the subshell to which the last electron is added
3. Name of that subshell is the required name of the block
1. S.E.C → 1s22s2
2. Subshell to which the last electron is added → s
3. Required name of the block → s
• So beryllium resides in the s-block
■ 26Fe
1. S.E.C → 1s22s22p63s23p64s23d6
2. Subshell to which the last electron is added → d [∵ based on fig.9.1(c), 4s is completely filled up before filling of 3d begins]
3. Required name of the block → d
• So iron resides in the d-block
■ 18Ar
1. S.E.C → 1s22s22p63s23p6
2. Subshell to which the last electron is added → p
3. Required name of the block → p
• So argon resides in the p-block
■ Element: 4Be
1. Atomic number: 4
2. S.E.C: 1s22s2
3. Highest shell number in the S.E.C: 2
4. Period number: 2
■ Element: 6C
1. Atomic number: 6
2. S.E.C: 1s22s22p2
3. Highest shell number in the S.E.C: 2
4. Period number: 2
■ Element: 11Na
1. Atomic number: 11
2. S.E.C: 1s22s22p63s1
3. Highest shell number in the S.E.C: 3
4. Period number: 3
■ Element: 19K
1. Atomic number: 19
2. S.E.C: 1s22s22p63s23p64s1
3. Highest shell number in the S.E.C: 4
4. Period number: 4
♦ Highest shell number in the S.E.C
♦ Period number of the element.
• As these two items are same for every element, we can write it as a rule. This rule can be written in steps.
Rule 9.2:
■ Given any element. We want to know the period in which that element resides in the periodic table (that is, the period number of the element). For that, use the following steps:
1. Write the S.E.C.
2. Find the highest shell number in the S.E.C
3. That shell number is the required period number
Arrangement of elements into Blocks
The following fig.9.2 shows that, all the elements in the periodic table are classified into four blocks. They are: s-block, p-block, d-block and f-block. |
| Fig.9.2 |
• We want to know the basis of such a classification. Let us analyse:
Following are some elements taken at random from the periodic table. Some details are also written about them:
■ Element: 3Li
1. Atomic number: 3
2. S.E.C: 1s22s1
3. Subshell to which the last electron is added: s
4. Block: s-block
■ Element: 12Mg
1. Atomic number: 12
2. S.E.C: 1s22s22p63s2
3. Subshell to which the last electron is added: s
4. Block: s-block
■ Element: 7N
1. Atomic number: 7
2. S.E.C: 1s22s22p3
3. Subshell to which the last electron is added: p
4. Block: p-block
■ Element: 21Sc
1. Atomic number: 21
2. S.E.C: 1s22s22p63s23p64s23d1
3. Subshell to which the last electron is added: d
4. Block: d-block
• We can see that items (3) and (4) are the same for all the elements.
• That means, the following two items are same for all the elements:♦ Subshell to which the last electron is added
♦ The block in which the element resides in the periodic table.
• As these two items are same for every element, we can write it as a rule. This rule can be written in steps.
Rule 9.1:
■ Given any element. We want to know the block in which that element resides in the periodic table. For that, use the following steps:
1. Write the S.E.C.
2. Find the subshell to which the last electron is added
3. Name of that subshell is the required name of the block
Some examples:
■ 4Be1. S.E.C → 1s22s2
2. Subshell to which the last electron is added → s
3. Required name of the block → s
• So beryllium resides in the s-block
■ 26Fe
1. S.E.C → 1s22s22p63s23p64s23d6
2. Subshell to which the last electron is added → d [∵ based on fig.9.1(c), 4s is completely filled up before filling of 3d begins]
3. Required name of the block → d
• So iron resides in the d-block
■ 18Ar
1. S.E.C → 1s22s22p63s23p6
2. Subshell to which the last electron is added → p
3. Required name of the block → p
• So argon resides in the p-block
Arrangement of elements into Periods
Following are some elements taken at random from the periodic table. Some details are also written about them:■ Element: 4Be
1. Atomic number: 4
2. S.E.C: 1s22s2
3. Highest shell number in the S.E.C: 2
4. Period number: 2
■ Element: 6C
1. Atomic number: 6
2. S.E.C: 1s22s22p2
3. Highest shell number in the S.E.C: 2
4. Period number: 2
■ Element: 11Na
1. Atomic number: 11
2. S.E.C: 1s22s22p63s1
3. Highest shell number in the S.E.C: 3
4. Period number: 3
■ Element: 19K
1. Atomic number: 19
2. S.E.C: 1s22s22p63s23p64s1
3. Highest shell number in the S.E.C: 4
4. Period number: 4
• We can see that items (3) and (4) are the same for all the elements.
• That means, the following two items are same for all the elements:♦ Highest shell number in the S.E.C
♦ Period number of the element.
• As these two items are same for every element, we can write it as a rule. This rule can be written in steps.
Rule 9.2:
■ Given any element. We want to know the period in which that element resides in the periodic table (that is, the period number of the element). For that, use the following steps:
1. Write the S.E.C.
2. Find the highest shell number in the S.E.C
3. That shell number is the required period number
So we saw how to find the 'Block name' and 'Period number' from the S.E.C. In the next section, we will see how to find the 'Group number' from the S.E.C.
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