Question

Valency of Boron in $B{{F}_{3}}$molecule is_________
A. Zero
B. One
C. Two
D. Three

Answer 1

Hint: Valency of an element is determined by following octet rule. Every element wants to get in stable form like noble gases. That’s why we get valence element forms.

Complete answer:
Valency: The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element. Valency is a measure of the ability of an atom to bond with other atoms.
How to Find Valency of Elements?
1. As we know, the number of electrons in the outermost shell of sodium is 1, and in chlorine, it is 7. Therefore the valency of sodium is 1 as it can easily lose 1 electron and become stable. On the other hand, chlorine is also 1 as it can accept 1 electron easily and also attain stability Furthermore, it is not only determined when an atom loses an electron. For example, chlorine has 7 electrons in its outermost orbital. It is hard to lose 7 electrons and so it completes its octet by gaining 1 electron. Since it gains 1 electron, its valency is 1. In the periodic table, the elements in the same group have the same valency.
2. For example, all the elements in group 8 have 8 electrons and completely filled orbitals, that is why the valency of all the elements in this group is zero.
3. Now we should come back to our question about finding the valency of boron in $B{{F}_{3}}$ .
4. Boron atomic number is 5. So by applying octet rule we get:-
In K shell – 2 electrons
L shell – 3 electrons
As in outer shells it has 3 electrons which is less than 5, so it has to release or donate these electrons for stability.
So valency of Boron in $B{{F}_{3}}$ is 3

Option D is correct.

Additional information:
Noble gases have a completely filled outermost shell and that’s why they are least reactive. Other element’s reactivity depends upon their ability to attain the noble gas configuration. If the outermost shell has 8 electrons then the element is said to have a complete octet. By gaining, sharing and losing the electrons the atoms complete their outermost orbital and make an octet. The reactivity of an atom is described by the total number of electrons lost, gained or shared to complete its octet and it also determines the valency of the atom.

Note: Difference between Valency and Oxidation Number: Valency is different from the oxidation number, and it has no sign.
For example, the valency of nitrogen is 3, whereas it can have oxidation numbers from -3 to +5. The oxidation number is the hypothetical charge of an atom in a molecule or ion, and it is a measure of its apparent capacity to gain or lose electrons within that species.