Name: The d-block Elements
Uploaded: 2019-07-19
Duration: 8 min 21 s
Description: The periodic table started with elements arranged in increasing order of Z. Now, it can tell us much more about an element. Watch this video to learn more.

Question

(i) Why do transition metals show variable states?

(ii) Chromium is very hard but mercury is a liquid. Why?

Accepted Answer

(i) Transition metals with variable Oxidation states: The elements in the same vertical column generally show similar oxidation states. but in a period the number of oxidation states shows variation. The elements in the middle of each series has maximum while elements have minimum at the extreme ends.However, $+ 2 and + 3$ oxidation states are quite stable for all elements present in the first transition series.All metals present in the first transition series form stable compounds in the $+ 2 and + 3$ oxidation states.The stability of the $+ 2 and + 3$ oxidation states decreases in the second and the third transition series, wherein higher oxidation states are more important.

For example ${[Fe {(CN)}_{6}]^{4 -}, [Co (NH}_{3})_{6}]^{3 +}, [Ti {(H_{2} O)}_{6}]^{3 +}$ are stable complexes, but no such complexes are known for the second and third transition series such as $Mo, W, Rh, In .$

They form complexes in which their oxidation states are high. For example: ${WCl}_{6}, {ReF}_{7}, {RuO}_{4}, etc .$

(ii) Chromium is hard because if we study its electronic configuration then it is $[Ar] 3 d ⁵ 4 s ¹$ , it has five unpaired d electrons in the d-sub-shell. Hence, metallic bonds are very strong due to more overlapping of valence shell to form bond.

Mercury-the liquid metal has electronic configuration $[Xe] 4 f^{14} 5 d^{10} 6 s^{2}$ It is the only transition metal that exists in its liquid state at room temperature. $6 s$ valence electrons of Mercury are more closely pulled by the nucleus (lanthanide contraction) such that outer s-electrons are less involved in metallic bonding.

(i) Why do transition metals show variable states?

(ii) Chromium is very hard but mercury is a liquid. Why?

Important Questions on d- and f-Block Elements

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