(i) Give reason for the following :
(a) Atomic mass of chlorine is a fraction and not a whole number
(b) Chemical properties of isotopes of the same element are similar
(c) Sodium is reactive whereas neon is unreactive
(d) Oxygen needs two electrons to attain nearest stable electronic configuration
(e) The group whose elements have zero valency
(ii) Atomic numbers of the following elements are given below: (5)
A= 1 , B = 19, C= 15 , D= 17 , E = 8
Answers
Answer:
(a) Atomic mass of chlorine is a fraction and not a whole number
The answer to why chlorine has an atomic weight of 35.5 not 35 is because of something called isotopes.
Isotopes are atoms with the same number of protons (in the case of chlorine that means 17 protons) but different numbers of neutrons.
Chlorine has two common isotopes, Chlorine-35 and Chlorine-37.
(b) Chemical properties of isotopes of the same element are similar
Usually one or two isotopes of an element are the most stable and common. Different isotopes of an element generally have the same physical and chemical properties because they have the same numbers of protons and electrons.
(c) Sodium is reactive whereas neon is unreactive
So, it shows almost no reactivity. sodium has one electron more(2,8,1) and fluorine has 1 electron less(2,7) But neon has a stable configuration(2,8,8). Neon has full valence shell so does not need to react to gain or lose electrons while and potassium does that is why neon shows no reactivity
(d) Oxygen needs two electrons to attain nearest stable electronic configuration
Oxygen atom attains stable electronic configuration of nearest noble gas-Neon by accepting two electrons in its valence shell and becomes positively charged oxide ion.