Answer

Verified

45.9k+ views

Hint: Look at the formula and try to determine the charges on the individual cations and anions that form the given compound. That way, you will be able to determine the valence shown by the cation and the anion.

> Since the valence of the fluoride ion is 1, thus the answer is (a). This poses the question, what exactly is valency or valence. The valency or valence of an element is defined as its combining power when it combines which other atoms or a group of atoms in a compound. > This combining power is determined by the number of hydrogen atoms that it combines with. For example carbon has a valency of 4 since it combines with four hydrogen atoms to give methane, oxygen has a valency of 2 since it combines with two oxygen atoms to give water, Nitrogen has a valency of 3 since it combines with three hydrogen atoms to give ammonia, Chlorine has a valency of 1 since it combines with one hydrogen atom to give hydrogen chloride.

> The elements that have one, two, three or four electrons in their outermost shell or valence shell, they have the valency of one, two, three and four respectively. For elements having more than 4 electrons in their valence shell, their valency can be easily found by using the formula:

Valency = 8-number of electrons in the valence shell.

Thus oxygen which has 6 electrons in its outermost shell has a valency of 2 (8-6=2). Chlorine which has seven electrons in its valence shell has a valency of 1 (8-7=1).

Now, if a metal A has a valency of 2, then its oxide formula will be ${AO}$ since both of them have a valency of 2 and therefore they will cancel out each other while writing the formula. Generally you should follow the following rules while writing the formula of a compound:

-Determine the valency of the two species involved. If they are anions or cations such as phosphate ion or sulphate ion, then their valence is equal to the magnitude of their charge.

-Cross multiply the valency of the two species in the simplest ratio.

$\begin{matrix} Species: \\ Valence: \end{matrix}\begin{matrix} A \\ 2 \end{matrix}+\begin{matrix} B \\ 3 \end{matrix}\xrightarrow { Cross\quad multiply\quad 2\quad and\quad 3\quad in\quad the\quad simplest\quad ratio } { A }_{ 3 }{ B }_{ 2 }$

For the given species ${ CaF }_{ 2 }$ using the above method in reverse order, we come to know that the valence of fluorine is 1 or its anionic form is ${ F }^{ 1- }$. Therefore the formula for the fluoride of calcium will be ${ CaF }_{ 2 }$ since calcium ion has the valence of 2.

$\begin{matrix} Species: \\ Valence: \end{matrix}\begin{matrix} { Ca }^{ 2+ } \\ 2 \end{matrix}+\begin{matrix} { F }^{ - } \\ 1 \end{matrix}\xrightarrow { Cross\quad multiply\quad 2\quad and\quad 1\quad in\quad the\quad simplest\quad ratio } { CaF }_{ 2 }$

Therefore the correct answer is (a) 1.

Note: The valency of a species can never be negative, zero or a fraction, it is always a positive number. The valence of a species is not fixed. For example many of the p-block elements show different valencies since they can expand their valence using d and f orbitals.

__Complete step by step solution:__> Since the valence of the fluoride ion is 1, thus the answer is (a). This poses the question, what exactly is valency or valence. The valency or valence of an element is defined as its combining power when it combines which other atoms or a group of atoms in a compound. > This combining power is determined by the number of hydrogen atoms that it combines with. For example carbon has a valency of 4 since it combines with four hydrogen atoms to give methane, oxygen has a valency of 2 since it combines with two oxygen atoms to give water, Nitrogen has a valency of 3 since it combines with three hydrogen atoms to give ammonia, Chlorine has a valency of 1 since it combines with one hydrogen atom to give hydrogen chloride.

> The elements that have one, two, three or four electrons in their outermost shell or valence shell, they have the valency of one, two, three and four respectively. For elements having more than 4 electrons in their valence shell, their valency can be easily found by using the formula:

Valency = 8-number of electrons in the valence shell.

Thus oxygen which has 6 electrons in its outermost shell has a valency of 2 (8-6=2). Chlorine which has seven electrons in its valence shell has a valency of 1 (8-7=1).

Now, if a metal A has a valency of 2, then its oxide formula will be ${AO}$ since both of them have a valency of 2 and therefore they will cancel out each other while writing the formula. Generally you should follow the following rules while writing the formula of a compound:

-Determine the valency of the two species involved. If they are anions or cations such as phosphate ion or sulphate ion, then their valence is equal to the magnitude of their charge.

-Cross multiply the valency of the two species in the simplest ratio.

$\begin{matrix} Species: \\ Valence: \end{matrix}\begin{matrix} A \\ 2 \end{matrix}+\begin{matrix} B \\ 3 \end{matrix}\xrightarrow { Cross\quad multiply\quad 2\quad and\quad 3\quad in\quad the\quad simplest\quad ratio } { A }_{ 3 }{ B }_{ 2 }$

For the given species ${ CaF }_{ 2 }$ using the above method in reverse order, we come to know that the valence of fluorine is 1 or its anionic form is ${ F }^{ 1- }$. Therefore the formula for the fluoride of calcium will be ${ CaF }_{ 2 }$ since calcium ion has the valence of 2.

$\begin{matrix} Species: \\ Valence: \end{matrix}\begin{matrix} { Ca }^{ 2+ } \\ 2 \end{matrix}+\begin{matrix} { F }^{ - } \\ 1 \end{matrix}\xrightarrow { Cross\quad multiply\quad 2\quad and\quad 1\quad in\quad the\quad simplest\quad ratio } { CaF }_{ 2 }$

Therefore the correct answer is (a) 1.

Note: The valency of a species can never be negative, zero or a fraction, it is always a positive number. The valence of a species is not fixed. For example many of the p-block elements show different valencies since they can expand their valence using d and f orbitals.

Recently Updated Pages

To get a maximum current in an external resistance class 1 physics JEE_Main

silver wire has diameter 04mm and resistivity 16 times class 12 physics JEE_Main

A parallel plate capacitor has a capacitance C When class 12 physics JEE_Main

A series combination of n1 capacitors each of value class 12 physics JEE_Main

When propyne is treated with aqueous H2SO4 in presence class 12 chemistry JEE_Main

Which of the following is not true in the case of motion class 12 physics JEE_Main

Other Pages

Differentiate between homogeneous and heterogeneous class 12 chemistry JEE_Main

Two identical particles each having a charge of 20 class 12 physics JEE_Main

If the mass of the bob of a simple pendulum increases class 11 physics JEE_Main

Excluding stoppages the speed of a bus is 54 kmph and class 11 maths JEE_Main

Electric field due to uniformly charged sphere class 12 physics JEE_Main

Explain the construction and working of a GeigerMuller class 12 physics JEE_Main