Question

Give the symbol for an element that is

1) a transtion metal in the fourth period from the following list: Ni, C, Os, Pm.

2) a metalloid.

3) a non-metal in group 4A, 5A, or 6A.

4) a lanthanide.

5) a metal in group 3A or 4A.

Answer 1

1. Transition metal of 4th period Ni[nickel at. no. = 28, elec. conf. 2,8,8, 8,2 , val. shell ele. conf. 3d⁸4s²

last e present in d-subshell, d-block elecment and val. elec. enter in 4th shell, therefore 4th period.

2. In general move down a group of p-block, metallc prop. increases and tends to non metal to metallic.

And in between metal and non-metal elements are called metalloid or semi-meatl, behaves as a metal as well as non-metal like (in-between), due to electronegativity,Ionisation energy also in-betweenof metal and non-metal.

ex: III group boron (B at.no. 5 val. elec.conf. 2s² 2p¹) and 4th group Silicon(at.no.14, 2,8,4 3S²3p²) and germanium(32, 4s2 4p2).

3. A non-metal in group 3A in III group we down the group from metalloid to metal here B= boron is metalloid and all other are metals, therefore B- may be considering non-metal also.

ii) 4A: Carbon- C at no. 6, (2,4) is non-metal due to high I E. and High electronegativity.

iii) 5A: Nitrogen (N at. no. 7, (2,5) and P (phosphorous at.no. 15 (2,8,5 ) also

iv)6A: Oxygen (O, at.no. 8(2,6)and S(sulphur 16 (2,8,6).

4) A lanthanide- Ce (cerium at. no. 58 val. elec.in 4f¹)

5) A metal in group 3A: Alto Tl all are metal (Al- aluminium) at. no. 13,( 2,8,3)

4A: Sn-tin and Pb(lead) Val.shell elec. conf. (ns²np2).