With reference to first three periods of the periodic table.
(i) Noble gas with duplet arrangement of electrons
(ii) Metalloid in 3rd period.
(iii) Valency of elements in group 17.
(iv) Noble gas with electronic configuration of 2, 8.
Answers
With reference to first three periods of the periodic table,
(i) The noble gas with a duplet arrangement of electrons is Helium.
(ii) A metalloid in the 3rd period is Silicon.
(iii) Valency of elements in group 17 is -1 .
(iv) Noble gas with an electronic configuration of 2, 8 is Neon.
i) • Duplet arrangement of electrons means only two electrons in the first shell.
• The first three periods in the periodic table consist of three noble gases, namely, helium, neon, and argon.
• Among these, helium is the only gas which has two electrons, since its atomic number is two.
• Neon has an atomic number of 10, and argon has an atomic number of 18.
• Therefore, the noble gas with a duplet arrangement of electrons, in the first three periods, is helium.
ii) • A metalloid is an element that exhibits properties of both metals and non-metals.
• In period 3, silicon is the only metalloid present, because it has 4 electrons in its valence shell.
• The electronic configuration of silicon (14) is 2, 8, 4. The 4 valence electrons can either be donated, as in the case of a metal, or shared, as in the case of a non-metal.
• So, silicon is a metalloid.
iii) • Group 17 is actually group 7 in the modern periodic table.
• The number of valence electrons in an element is given by its group number.
• So, group 17 elements have 7 electrons in their valence shell.
• To complete the octet, they need to gain 1 more electron (1e-) in their valence shell.
• Therefore, group 17 elements have a valency of -1 .
iv) • Electronic configuration 2, 8 means the atomic number of the element is 2 + 8 = 10.
• The noble gas with atomic number is 10 is neon.