What is an atom,molecule and atomicity of a substance?

Atoms: The atom is the smallest indivisible particle of a substance that can’t exist independently, atom is also composed of subatomic particles protons, neutrons, and electrons. The subatomic particles proton, neutron, and electron were discovered by Goldstein, Chedwik, and J.J Thompson respectively. Although atoms and its subatomic particles can’t be seen directly by a device, scientists experiment on the observation of the different kinds of phenomena due to the content of matter shows the existence of atom and its subatomic particles. Atoms are as small as that even the tip of a needle can accommodate more than 1 lakh atoms.

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Molecules: A molecule is the smallest particle of a substance that exists independently and shows the characteristic of the substance. Molecules are composed of two or more than two atoms. In a molecule, atoms are bonded to each other with a covalent bond.

As an example, are the molecules of carbon dioxide, oxygen, and hydrogen respectively.

In the equation of chemical reaction molecules of a substance are represented for showing the involvement of the substance in the chemical reaction.

As an example

The size of molecule depends on the number of atoms available in it

What are Surds and how to compare them?

The atomicity: Atomicity of a substance is the number of atoms in its molecule. The atomicity of oxygen, hydrogen, Carbon dioxide and water is 2,2,3 and 3 respectively. If we know the molecular formula of a substance then we can easily calculate the atomicity of a substance.

Example: What are the atomicity of the following substance

(a) Sulphur (b) Phosphorus (c) Helium (d) Sodium Chloride (e) Potassium Chlorate (f) Calcium hydroxide (g) Nitric acid (f) Sulphuric acid

Ans. (a) Sulphur molecule has 8 atoms so its atomicity is 8

(b) Phosphorus molecule has 4 atoms so its atomicity is 4

(c) The formula of Sodium chloride (NaCl) shows that it has one atom of Na and 1 atom of Cl, so its atomicity is 2.

(d) The formula of Potassium Chlorate (KClO3) shows that it has one atom of K , 1 atom of Cl and 3 atoms of oxygen ,so its atomicity is 5.

(e) The formula of Calcium hydroxide Ca(OH)2 shows that it has one atom of Ca ,2 atoms of O, 2 atoms of H, so its atomicity is 5.

(f) The formula of Sulphuric acid (H2SO4) shows that it has 2 atoms of H and 1 atom of S and 4 atoms of O, so its atomicity is 2.

(h) The formula of aluminum sulphate Al2(SO4)3  shows that it has 2 atoms of Al, 3 atoms of sulphur, and 12 atoms of oxygen so its atomicity is 17.

Related questions on molecular mass, molar mass and moles.

Q1. What is the molecular mass of sodium nitrate?

Q2. How many moles are in 440 gm of carbon dioxide?

Q3. How many carbon atoms are in 1 kg of carbon dioxide?

Q4. How many sulphate ions are in 400 gm of aluminum sulphate?

Q5. What is the molar mass of Sodium carbonate?

Q6. What is the atomicity of calcium chloride?

Q7. How many moles are in electrons.

Q8. How many electrons are in 64 gm of oxygen gas?

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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

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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

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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

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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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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

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