Name a cation or a radical with valency '2'?
1 Answer
The cation Sr 2+ has a valency of 2.
Explanation:
Let's define what valency is first and foremost.
What is valency, you may ask? Valency is the number of outer electrons that can be determined by simply counting the number of outer electrons, called valence electrons , of any element or cation. If the number of valence electrons of an element or cation is less than or equal to 2 , the number of the outer electrons is simply its valency. If the number of valence electrons is greater than 2 , you can take 8 minuses the number of outer electrons to find the element's or cation's valency.
Here, strontium 2+ is a cation of the element strontium. Because its charge is 2 positive, strontium has to lose two electrons. For its atomic number is 38, its electron is 36. This is because initially, it has 38 electrons. It loses 2 electrons to be 2+. Ergo, 38 minuses 2 equals to 36 .
When you know the number of electrons of a cation, you can simply find its valency by the method above.
(For reference: If the number of valence electrons of an element or cation is less than or equal to 2, the number of the outer electrons is simply its valency. If the number of valence electrons is greater than 2, you can take 8 minuses the number of outer electrons to find the element's or cation's valency)
Following the Bohr's model of an atom, we know that the first shell must consist of 2 electrons, the second shell must consist of 8 electrons, and the third shell must consist of 8 electrons, and so on. What you want to do is take the number of electrons of the atom and minus the electrons of the shells needed to get to the outer shell.
In this case, strontium 2+ has 6 shells in total. The first shell it has 2 electrons. The second shell it has 8 electrons,...and so on until the sixth cell, where it has 2 electrons. Since 2 is less than or equal to 2, 2 is the valency of strontium 2+ .
--> Thus, Sr 2+ is a cation with a valency of '2'.
DISCLAIMER: You can also use the periodic table to determine an atom's valency by its group (column) in the periodic table. Since strontium is in group 2, its valency is automatically 2.
