Q.3 (vi) Write the names from the description :
(a) The metalloids in the second and third period.
(b) Non-metals in the third period.
(c) Two elements having valency 4.
Best answer
Answer: (a) Boron (B) and silicon (Si); (b) phosphorus (P), sulphur (S) and chlorine (Cl); (c) carbon (C) and silicon (Si).
(a) The metalloids are the elements which show properties of both metals and non-metals. In the second period it is boron and in the third period it is silicon (germanium and arsenic are the other metalloids).
(b) The third period runs from sodium to argon. Its non-metals are phosphorus, sulphur, chlorine and argon (a noble gas).
(c) Elements with four valence electrons show a valency of 4. Carbon (2, 4) and silicon (2, 8, 4) both have valency 4 and form covalent compounds such as CH4 and SiH4.
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