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 $\boldsymbol{Ca\left ( OH \right )_{2}}$

NCERT Solutions of Science and Maths for Class 9,10,11 and 12

NCERT Solutions for class 9 maths

Chapter 1- Number System	Chapter 9-Areas of parallelogram and triangles
Chapter 2-Polynomial	Chapter 10-Circles
Chapter 3- Coordinate Geometry	Chapter 11-Construction
Chapter 4- Linear equations in two variables	Chapter 12-Heron’s Formula
Chapter 5- Introduction to Euclid’s Geometry	Chapter 13-Surface Areas and Volumes
Chapter 6-Lines and Angles	Chapter 14-Statistics
Chapter 7-Triangles	Chapter 15-Probability
Chapter 8- Quadrilateral

NCERT Solutions for class 9 science

Chapter 1-Matter in our surroundings	Chapter 9- Force and laws of motion
Chapter 2-Is matter around us pure?	Chapter 10- Gravitation
Chapter3- Atoms and Molecules	Chapter 11- Work and Energy
Chapter 4-Structure of the Atom	Chapter 12- Sound
Chapter 5-Fundamental unit of life	Chapter 13-Why do we fall ill ?
Chapter 6- Tissues	Chapter 14- Natural Resources
Chapter 7- Diversity in living organism	Chapter 15-Improvement in food resources
Chapter 8- Motion	Last years question papers & sample papers

NCERT Solutions for class 10 maths

Chapter 1-Real number	Chapter 9-Some application of Trigonometry
Chapter 2-Polynomial	Chapter 10-Circles
Chapter 3-Linear equations	Chapter 11- Construction
Chapter 4- Quadratic equations	Chapter 12-Area related to circle
Chapter 5-Arithmetic Progression	Chapter 13-Surface areas and Volume
Chapter 6-Triangle	Chapter 14-Statistics
Chapter 7- Co-ordinate geometry	Chapter 15-Probability
Chapter 8-Trigonometry

CBSE Class 10-Question paper of maths 2021 with solutions

CBSE Class 10-Half yearly question paper of maths 2020 with solutions

CBSE Class 10 -Question paper of maths 2020 with solutions

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NCERT Solutions for Class 10 Science

Chapter 1- Chemical reactions and equations	Chapter 9- Heredity and Evolution
Chapter 2- Acid, Base and Salt	Chapter 10- Light reflection and refraction
Chapter 3- Metals and Non-Metals	Chapter 11- Human eye and colorful world
Chapter 4- Carbon and its Compounds	Chapter 12- Electricity
Chapter 5-Periodic classification of elements	Chapter 13-Magnetic effect of electric current
Chapter 6- Life Process	Chapter 14-Sources of Energy
Chapter 7-Control and Coordination	Chapter 15-Environment
Chapter 8- How do organisms reproduce?	Chapter 16-Management of Natural Resources

NCERT Solutions for class 11 maths

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

CBSE Class 11-Question paper of maths 2015

CBSE Class 11 – Second unit test of maths 2021 with solutions

NCERT solutions for class 12 maths

Chapter 1-Relations and Functions	Chapter 9-Differential Equations
Chapter 2-Inverse Trigonometric Functions	Chapter 10-Vector Algebra
Chapter 3-Matrices	Chapter 11 – Three Dimensional Geometry
Chapter 4-Determinants	Chapter 12-Linear Programming
Chapter 5- Continuity and Differentiability	Chapter 13-Probability
Chapter 6- Application of Derivation	CBSE Class 12- Question paper of maths 2021 with solutions
Chapter 7- Integrals
Chapter 8-Application of Integrals