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# How to determine Valency,net charge of an ion and Molecular formula of a substance.

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Valency: Valency of an element is the holding capacity of an atom of a substance, as we know atom is neutral then how is this capable to react with other atoms of a substance? The reaction of an atom of an element with other atoms is decided by the electrons available in its outermost orbital called valence electrons of an atom. Every atom of a substance has a tendency to have 8 electrons in its outermost orbits, so an atom of a substance can either loss or gains the electrons. When an atom of an element comes in contact with another particular atom, both of them excited to exchange or share the electrons and form molecules. As an example the formation of sodium chloride.

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The electronic configuration of Na(11)  is= 2,8,1 and of chlorine (17) is =2,8,7

When Na atom comes in contact with Cl atom both of them excited and form ions, the charged particles. It is clear from the electronic configuration of both the atoms that Na losses 1 electron to make an octet in its outermost orbit and Cl atom gains 1 electron to make octet in its outermost orbit.therefore after losing 1e Na forms $\boldsymbol{Na^{+}}$ ion and After a gain of 1e Chlorine forms $\boldsymbol{Cl^{-}}$ ion.

$\boldsymbol{Na\rightarrow Na^{+}+e},\: \boldsymbol{\: Cl+e\rightarrow Cl^{-}}$

As we know opposite charges attracted each other and so both $\boldsymbol{Na^{+}}$ and $\boldsymbol{Cl^{-}}$ attracted and stuck together and forms a molecule of sodium chloride and such type of bonds between two ions is known as ionic bond.

In the formation of carbon dioxide molecule when carbon atom and oxygen comes in contact with each other in a particular circumstance, they share electrons with each other because carbon can not form ions since it is requiring large amount of energy in exchanging its 4 outermost electrons.

Here, in this case, carbon atoms and oxygen molecules share electrons in fulfilling their outermost orbit. Sharing means, now electrons of carbon and oxygen atoms can enter into each other’s orbits and such type of chemical bond is known as Covalent bond.

## Net Charge of an ion

Ions are of two kinds on the basis of the number of atoms (a) Mono-atomic ions (b) Polyatomic ions. Monoatomic ions are made of a single atom and Polyatomic ions are made of more than one atoms, when whole of the molecule of a substance ionized then polyatomic ions are formed.These polyatomic ions are also called radicals. The atoms in these polyatomic ions are bonded with covalent bonds and have net charge.

The net charge of polyatomic ions is the sum of charges(or valency) of individual atoms  in it, as an example

.$\boldsymbol{SO_{4}^{-2}}$

The charge in a sulphur atom is +6 because it shares its 6 electrons to 4 oxygen atoms charge in 4 oxygen atoms = -2×4=-8, so the net charge of sulphate ion is =-8 + 6= -2.

## The molecular formula of a substance:

The molecular formula of a substance shows the proportions of all elements in a substance,as an example from the formula of water $\boldsymbol{H_{2}O}$  we can get the volumes and masses wise ratio of hydrogen and oxygen in the water.

The mass of two hydrogen atoms in  water is = 1×2= 2u and of one oxygen atom is =16

The ratio of hydrogen and oxygen in water is = 1: 8

Volume-wise ratio = number of hydrogen atoms: number of oxygen atoms=2: 1

The chemical or molecular formula of a substance is determined by the valency or charges of atoms and ions. Let the valency of a substance X is 2 and of Y substance is 3 then the chemical formula of the substance formed by them is X3Y2.

As an example calcium hydroxide

Valency of Ca  is = 2 and the net charge of Hydroxide ion is =-1

Then the number of atoms involved in the formation of a molecule depends on the charges on another atom or radical, as example net charge of hydroxide ion (-1) compels one atom of Ca to combine in it, and charge 2 of Ca compel one ion of  OH to combine in it.

Therefore the chemical formula for calcium hydroxide is $\boldsymbol{Ca\left ( OH \right )_{2}}$

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 Chapter 1-Sets Chapter 9-Sequences and Series Chapter 2- Relations and functions Chapter 10- Straight Lines Chapter 3- Trigonometry Chapter 11-Conic Sections Chapter 4-Principle of mathematical induction Chapter 12-Introduction to three Dimensional Geometry Chapter 5-Complex numbers Chapter 13- Limits and Derivatives Chapter 6- Linear Inequalities Chapter 14-Mathematical Reasoning Chapter 7- Permutations and Combinations Chapter 15- Statistics Chapter 8- Binomial Theorem Chapter 16- Probability

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