Element having variable valency 1 and 3?

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Answer 1 · 2017-07-10T19:49:49

Thallium and gold have valencies of 1 and 3.

Thallium

Thallium is about 170 times as abundant as gold in the Earth's crust.

The electron configuration of thallium is ${[Xe] 6s}^{2} 4 f^{14} {5d}^{10} 6p$ $"[Xe] 6s"^2 4"f"^14 "5d"^10 "6p"$ .

It is easy to remove the $6p$ $"6p"$ electron and form ${Tl}^{+}$ $"Tl"^"+"$ .

The $6s$ $"6s"$ subshell contains the next-most easily removed electrons.

Removal of these electrons gives ${Tl}^{3+}$ $"Tl"^"3+"$ with electron configuration $[Xe] 4 f^{14} {5d}^{10}$ $"[Xe] 4"f^14 "5d"^10$ .

Thus, some common compounds of thallium are:

Gold

The electron configuration of gold is $[Xe] 6s 4 f^{14} {5d}^{10}$ $"[Xe] 6s 4"f^14 "5d"^10$ .

It is easy to remove the $6s$ $"6s"$ electron and form ${Au}^{+}$ $"Au"^"+"$ .

The $5d$ $"5d"$ subshell contains the next-most easily removed electrons.

Another common state of gold is ${Au}^{3+}$ $"Au"^"3+"$ with electron configuration $[Xe] 4 f^{14} {5d}^{8}$ $"[Xe] 4"f^14 "5d"^8$ .

Thus, the most common compounds of gold are

Here's a table giving the most common oxidation numbers of the elements in their compounds.

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