CBSE Class 9 Answered
(i) Define valency by taking the examples of magnesium (At. no. = 12) and oxygen (At. no. = 8)
(ii) S-2 has completely filled K, L and M shells. Find its atomic number.
Asked by Topperlearning User | 04 Apr, 2016, 10:02: AM
Expert Answer
(i)The combining capacity of an element is called its valency.
Magnesium has atomic number 12 and electronic configuration is 2, 8, 2. It can lose 2 electrons to get the octet configuration in the outermost shell thus its valency is 2.
Oxygen has atomic number 8 and its electronic configuration is 2, 6.
It can gain 2 electrons to get the octet configuration in the outermost shell thus its valency is 8 - 6 = 2.
(ii) K = 2, L = 8
Now, M i.e. the outermost shell can have only eight electrons and since S has -2 charge hence the number of electrons in M shell = 8.
So, the atomic number is equal to number of electrons thus atomic number of S2- ion is 18.
Answered by | 04 Apr, 2016, 12:02: PM
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