# Element having variable valency 1 and 3?

Jul 10, 2017

Thallium and gold have valencies of 1 and 3.

#### Explanation:

Thallium

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

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

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

The $\text{6s}$ subshell contains the next-most easily removed electrons.

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

Thus, some common compounds of thallium are:

• thallium(I) sulfide $\text{Tl"_2"S}$,
• thallium(I) sulfate ${\text{Tl"_2"SO}}_{4}$
• thallium(III) fluoride ${\text{TlF}}_{3}$
• thallium(III) oxide ${\text{Tl"_2"O}}_{3}$

Gold

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

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

The $\text{5d}$ subshell contains the next-most easily removed electrons.

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

Thus, the most common compounds of gold are

• gold(I) chloride $\text{AuCl}$
• gold(III) chloride ${\text{AuCl}}_{3}$
• chlorauric acid ${\text{HAuCl}}_{4}$

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