How are helium atoms and neon atoms useful in predicting the structure of a sodium atom?

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Helium has an atomic number of 2 and has an electronic configuration of 1s2. Neon is also a noble gas and has an atomic number of 10. Hence, its electronic configuration is 1s2, 2s2, 2p6. Sodium has an atomic number of 11 and hence has an electronic configuration of 1s2,...

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Helium has an atomic number of 2 and has an electronic configuration of 1s2. Neon is also a noble gas and has an atomic number of 10. Hence, its electronic configuration is 1s2, 2s2, 2p6. Sodium has an atomic number of 11 and hence has an electronic configuration of 1s2, 2s2, 2p6, 3s1.

If we compare sodium and neon, we find that sodium is obtained by adding 1 more electron to neon atoms. There is an additional 3s orbital as compared to neon, or we can also state that an additional shell is present in case of sodium, as compared to neon. In comparison to helium, sodium has 2 additional electron shells. Hence, these two atoms help us gain a better understanding of the structure of sodium atoms. 

Compared to these two noble gases, sodium has unfilled valence electronic orbital and loses an electron to achieve noble gas configuration.

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