How can we do electrinic configuration of bromine class 10 as we don't know spdf rule??

Dear Student

Writing electronic configuration of an element using Aufbau principle is called spdf rule.

Thus the order of energy of an orbital is ,   1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p < 6f < 7d < …….

For ex.,
Sl. No Elements Symbol Atomic number Electronic configuration
1. Hydrogen H 1 1s1
2. Helium He 2 1s2
3. Lithium Li 3 1s2, 2s1
4. Beryllium Be 4 1s2, 2s2
5. Boron B 5 1s2, 2s2 2p1
6. Carbon C 6 1s2, 2s2 2p2
7. Nitrogen N 7 1s2, 2s2 2p3

The valency is decided by the number of electrons in the valence shell. For ex., valency of nitrogen is either 3 or 5, carbon is 4, boron is 3.  
Similarly,
Atomic number of bromine is 35.

Electronic configuration - Br 35- 1s22s22p63s23p64s23d104p5I53 -[ Kr] 4d10 5s2 5p5

​​​​​​​Regards

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