Question

The atom of an element has the electron structure 2, 7.
(a) What is the atomic number of the element?
(b) To which of the following would it be chemically similar?
₇N, ₁₅P, ₁₇Cl, ₁₈Ar
(c) Why would you expect it to be similar?

Answer 1

(a) The atomic number of the element is 9.

(b) Out of given options, ₁₇Cl has similar properties with this element.
Electronic configuration of Cl is 2, 8, 7. So, valence shell contains 7 electrons.

(c) The modern periodic table assumes that elements with the same number of valence electrons have similar properties.