write the electronic con figuration of elements having atomic number 17 and 21. Then find the period,group and block of these elements?
Answers
Explanation:
For finding block- 1. Write the electronic configuration. 2. See the block in which the last electron enters. The element will belong to that block. Eg: atomic no.
This is the most common difficulty of Class 10 and further 11–12th science students. I have made notes on this trick in the most possible easy way to provide solution to all :
V.E => Valence Electrons i.e Electrons in the last shell
How to find no. of shells in electronic configuration ?
If Atomic no = 30 , divide it as 2, 8, 8, 18, 18, 32, 32 so we get 2, 8, 8, 12 => As you get 4 numbers here ,means 4 shells i.e K,L,M,N . So 4 shells mean 4th period. that’s it :)
Example for 3 digit Atomic no
Atomic no : 103
Period can be found as explained.
Group will be last two digits of 103 means 03 , i.e 3rd group. Cool na !!
Now for class 11th and 12th
TO FIND GROUP & PERIOD & BLOCK FROM ELECTRONIC CONFIGURATION
1. To find the period number Write electronic configuration, Maximum value of n is period
2. To find the group number
S block - No of electrons in ns
P block - No of electrons in ns + np + 10
D block - No of electrons in ns + (n-1)d
F block - 6th period - 58 to 71 , 7th period - 90 to 103
3. For block : See the block in the last orbital
Examples :
1.Atomic number - 20
1s2, 2s2, 2p6, 3s2, 3p6, 4s2
Last electron is in 4s - It means element belongs to s-block
For s-block = g.p no => No of electrons in ns i.e 2 (here)
G.p no = 2
Period no = 4
Block - s (see highest orbital 4s, so s)
2. Atomic number - 15
1s2, 2s2, 2p6, 3s2, 3p3
Last electron is in 3p - It means element belongs to p-block
For p-block = g.p no => No of electrons in ns + np + 10
Therefore, 2 + 3 + 10 = 15
G.p no = 15
Period no = 3
Block - p (see highest orbital 3p, so p)
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