(a) State the rule according to which electrons are filled in various energy levels.

(b) Give the number of electrons that can be present in the first four shells of an atom using this rule.

(c) What is the maximum number of electrons present in the outermost (valence) shell ?

What are isotopes? How does the existence of isotopes contradict Dalton's atomic theory?

State the mass number, the atomic number, number of neutrons and electronic configuration of the following atoms.

(a) ¹²C₆

(b) ¹⁶O₈

(c) ¹⁹F₉

(d) ²⁰Ne₁₀

(e) ²⁷Al₁₃

(f) ³⁵Cl₁₇

Also, draw atomic diagrams for each of them.

Draw the diagrams representing the atomic structures of the following:

(a) Nitrogen

(b) Neon