Question

electronic configuration of first 20 elements. Also write composition of atoms i.e. number of protons , electrons and neutrons .

Answer 1

1. Atomic Number = Number of electrons = Number of protons .

2. The first 20 elements with there electronic configuration are as follows:

S.No	Name	Atomic Number	Electronic Configuration
1.	Hydrogen	1	1s1
2.	Helium	2	1s2
3.	Lithium	3	1s​22s1
4.	Beryllium	4	1s22s2
5.	Boron	5	1s22s​22p​1
6.	Carbon	6	1s​22s22p2
7.	Nitrogen	7	1s​22s22p3
8.	Oxygen	8	1s​22s22p4
9.	Fluorine	9	1s​22s22p5
10.	Neon	10	1s​22s22p6
11.	Sodium	11	1s​22s22p63s1
12.	Magnesium	12	1s​22s22p63s2
13.	Aluminium	13	1s​22s22p63s23p1
14.	Silicon	14	1s​22s22p63s23p2
15.	Phosphorous	15	1s​22s22p63s23p3
16.	Sulphur	16	1s​22s22p63s23p4
17.	Chlorine	17	1s​22s22p63s23p5
18.	Argon	18	1s​22s22p63s23p6
19.	Potassium	19	1s​22s22p63s23p64s1

20. Calcium 20 1s^​22s²2p⁶3s²3p⁶4s2

3. Numer of neutrons = Mass number - Atomic number.