CBSE Class 11 Chemistry Revision Notes Chapter 1

CBSE Class 11 Chemistry Chapter 1 Notes

Students will learn that each chemistry concept, including the equations, diagrams, and crucial questions, is explained in detail in these CBSE Chemistry Notes for Class 11. They will be given a brief overview of the key concepts and formulas. Additionally, students can quickly revise these notes before exams.

Notes for Class 11 Chemistry Chapter 1: Some Basic Concepts of Chemistry

Students need to understand Class 11 Chapter 1: Some Basic Concepts of Chemistry because it lays the foundation for understanding the process of chemical reactions that occur everywhere. Students can learn more about these topics by referring to Extramarks Class 11 Chemistry Chapter 1 Notes. The Chemistry Class 11 Chapter 1 Notes were written by subject matter experts in clear, simple language so that every student can understand and use them while preparing for exams.

Access Class 11 Chemistry Chapter 1- Some Basic Concepts of Chemistry Notes

  1. Chemistry

Chemistry is a branch of science that deals with the study of how matter is made up, how it behaves, and how it changes as a result of chemical reactions. The word chemistry is derived from the Egyptian word kēme (chem), which means “earth.” Chemistry is commonly referred to as a “core science” due to its role in uniting physical sciences, such as itself with the life sciences and applied sciences (such as medicine and engineering).

Roald Hoffmann defines Chemistry as “the science of molecules and their transformations”. It is the science not so much of the one hundred elements but of the infinite variety of molecules that may be built from them.”

Chemistry is divided into the following branches:

Physical Chemistry

This branch of chemistry deals with both physical and macroscopic phenomena in the universe. It is typically the effect of a physical property on a substance’s chemical property as well as its structure.

Organic Chemistry

Organic chemistry is the field of study that examines the composition, structure, and chemical characteristics of organic compounds. It entails the investigation of carbon and its byproducts.

Inorganic Chemistry

Inorganic chemistry is the branch of chemistry that focuses on compounds free of carbon and hydrogen atoms. In a nutshell, it is the antithesis of organic chemistry. Metals, salts, and chemicals are examples of substances that do not contain carbon-hydrogen bonds.


As a branch of chemistry, biochemistry investigates the chemical processes that occur within and around living things. This laboratory-based science combines biology and chemistry. Biochemists can comprehend and address biological issues using their knowledge of and expertise in the chemical sciences.

Analytical Chemistry

It is the branch of Chemistry that uses equipment and analytical methods to ascertain a substance’s structure, functionality, and properties.

  1. Matter

Matter is a fundamental concept in chemistry. It refers to anything that has mass and occupies space. All living things like books, pens, pencils, water and air, are made of matter.

In general, there are three states of matter:

Solids: These are substances that have a distinct shape, maintain their volume according to that shape, and have the least amount of freedom of movement. For example, sugar, iron, gold, wood, etc.

Liquid: Liquid substances have a definite volume but lack a distinct shape. Additionally, liquids can pour or flow. In liquid substances, the particles can move around.  Examples include water, milk, oil, mercury, and alcohol.

Gas: Gases are substances that lack both a defined volume and a  shape. There is an easy and rapid movement of particles in gaseous substances. In general, gases fill their storage container to the brim. such as oxygen, hydrogen, etc.

If temperature and pressure are changed, these three states of matter can be interconverted.

  1. Classification of Matter at Macroscopic Level

Matter can also be classified at the bulk or macroscopic level as follows:


A mixture is a substance that contains two or more different substances in any combination. It mainly falls into two categories: heterogeneous mixtures and homogeneous mixtures.

Homogeneous mixture: When the two constituent substances are evenly distributed throughout the mixture, the mixture is said to be homogeneous. The compositions of the substances in a homogenous mixture are uniform. Air and a sugar solution are two examples of homogeneous mixtures.

Heterogeneous mixture: Heterogeneous mixtures are made up of two or more different substances that are distributed unevenly. The composition of substances in a heterogenous mixture is non-uniform. Examples include suspensions, which are combinations of two solids, such as salt and sugar.

Pure Substances: A substance is considered pure if it only contains one type of particle.

Note: In chemistry, forms of matter cannot be physically separated into their components because they have constant chemical compositions and properties.

Pure substances are further divided as given below:


An element is a pure substance containing only one kind of atom and cannot be broken down further. The elements are further separated into three classes based on their physical and chemical properties: (1) Metals (2) Non- metals and (3) Metalloids.

Compound: A compound is a pure material made of two or more elements combined in a specific mass ratio. Additionally, a compound’s properties are distinct from those of its component parts. Physical techniques cannot separate a compound’s constituent parts into simpler ones. Only chemical methods can separate them.

  1. Properties of Matter

The characteristics of every substance are unique and defining.

The two types of properties that are observed are physical properties and chemical properties.

Physical Properties

Physical characteristics are those that can be measured or observed without changing the identity or makeup of the substance. Examples of physical properties include colour, scent, melting and boiling points, density, and others.

Chemical Properties

The characteristics of particular substances that are observable in chemical reactions are known as their chemical properties. Some of the main chemical characteristics include chemical stability, flammability, toxicity, the heat of combustion, pH, and radioactive decay rate.

  1. Measurement

Physical Quantities 

When conducting scientific research, we come across physical quantities. Any physical quantity can be determined by measuring it twice:

(1) The number, and

(2)The unit: The unit is defined as the standard of measurement used to measure any physical quantity.

S.I. Units

The eleventh General Conference on Weights and Measures (CGPM from Conference Generale des Poids at Measures) established the International System of Units (in French, Le Systeme International d’Unités, abbreviated as SI).

The SI system consists of seven base units, which are listed below.

  • Unit of Length: Metre
  • Unit of Mass: Kilogram
  • Unit of Time: Second
  • Unit of Electric Current: Ampere
  • Unit of Thermodynamic Temperature: Kelvin
  • Unit of Amount of Substance: Mole
  • Unit of Luminous Intensity: Candela

The seven basic scientific quantities are represented by these units. These quantities can be used to calculate other physical quantities like speed, volume, density, etc. 

  1. Some Important Definitions

Mass and Weight

An object’s mass is a measure of how much matter makes up that object. The weight of an object is determined by the exertion of the force of gravity on the object. Mass remains constant and is location independent, while weight varies and depends on location.

The SI unit of mass is the kilogram (kg).

The SI-derived unit of weight is Newton.


The amount of three-dimensional space occupied or contained by a substance (solid, liquid, gas, or plasma) or shape that is bounded by specific closed boundaries. Volume is generally measured numerically using SI-derived units (cubic metres).


Density, or mass density, refers to a material’s mass per unit volume. The lowercase Greek letter rho (ρ) represents density. The SI uses the kg/m3 unit of density.


The common concepts of heat and cold are expressed quantitatively by the physical property of matter known as temperature. Celsius, Fahrenheit, and Kelvin are the three commonly used scales for measuring temperature (Kelvin). The following relationship describes how the temperature on two scales relates to one another:

F = 9/5 (C) + 32


  1. Law of Chemical Combination

Law of Conservation of Mass

“Mass is conserved” in a chemical reaction when the mass of the reactants consumed and the mass of the products produced are equal. This is a direct result of the law of conservation of atoms. The law was promulgated in 1789 by Antoine Lavoisier.

Law of Constant / Definite Proportions

According to the law of definite proportions, the elemental mass ratios in a composite sample are constant. This was offered by Joseph Proust, a French chemist.

Law of Multiple Proportions

When two elements are combined to create more than one compound, the law of multiple proportions states that each element’s fixed weight is proportional to the other element’s fixed weight when expressed as a whole number. This law was proposed by Dalton in 1803.

Law of Reciprocal Proportions

The law states that when two different elements are combined with a third element whose mass is fixed, their combined mass ratio will be the same or a straightforward multiple of their combined mass. This law was proposed by Richter in 1792.

Gay Lussac’s Law of Gaseous Volumes

According to Gay Lussac’s Law, which was postulated in 1808, states that a simple whole number can be used to represent the relationship between the volume of a gaseous reactant and a product.

Avogadro Law

Avogadro proposed in 1811 that gases of equal volumes and pressures should have an equal number of molecules in them.

  1. Dalton’s Atomic Theory

In his 1808 publication “A New System of Chemical Philosophy,” Dalton proposed the following ideas:

  • The unbroken building blocks of matter are called atoms.
  • The atoms of a given element are identical in all respects, including mass. Different elements have atoms with different masses.
  • Compounds are made when atoms from different elements combine in a particular ratio.
  • Chemical reactions allow for the self-rearrangement of atoms. Chemical interactions have no effect on these.
  1. Atom

The smallest unit that participates in a chemical reaction and retains the characteristics of an element is known as an atom. (Note: Only non-radioactive reactions are covered by this definition.)

  1. Molecules

They are the smallest components of a substance, possesses both its physical and chemical characteristics. One or more atoms make up molecules. E.g., H2, NH3.

A molecule’s mass is calculated by adding the masses of the individual atoms that make it up. As a result, the two units used to express the mass of an atom, amu and g/mol, can also be used to express the mass of a molecule.

  1. Chemical Reactions

A procedure that involves changing a substance’s molecular or ionic structure; distinct from a change in the substance’s physical form or a nuclear reaction.

  1. Stoichiometry

Stoichiometry is the study of chemical reactions and the associated calculations. The stoichiometric coefficient is the quantity that is used to balance the reaction.

  1. Percent Yield

The amount of product produced by the chemical reaction is less than that predicted by the theoretical calculation for practical reasons. The percentage yield is determined by multiplying the difference between the actual amount of product formed and the anticipated amount by 100.

  1. Reactions in Aqueous Media

The two solids must be dissolved in the liquid because they cannot interact with one another in the solid phase. A solution is a collective term that results from the dissolution of solutes in a solvent. The strength of the solution is measured using several variables. The strength of a solution can be used to estimate how much solute is present in it.

  1. Dilution Law

When a solution is diluted, its moles remain unchanged. If a solution’s volume is diluted from V1 to V2 with a Molarity of M1,

We can write the following by adding more solvent:

M1V1 = M2V2 = moles of the solute in the solution

  1. Effect of Temperature

The volume of the solvent grows as the temperature rises. However, if the system is closed, there won’t be any mass loss, and the quality of the solute in the solution won’t be affected. Temperature changes have no impact on the strength of solution formulas that do not include a volume of solution.

  1. Introduction to Equivalent Concept

Understanding chemical reactions and processes can be done by using the concept of equivalence, which is typically used to simplify things.

  1. Mixture of Acids and Bases

One can use the idea of equivalence to determine whether a solution is acidic or alkaline if it contains a mixture of different acids and bases. To determine which acid or base is in excess, find the equivalents of the ones that were used in the mixture.

  1. Law of Chemical Equivalence

This law states that in order to produce an equivalent of each product, an equivalent of one reactant must be combined with an equivalent of another reactant.

  1. Equivalent Weights of Salts

To calculate the equivalent weight of a compound that is neither an acid nor a base, one must know the charge of the cation or anion. The equivalent mass of a cation is equal to its mass divided by the charge that is attached to it, and the equivalent mass of an anion is equal to its mass divided by the charge that is attached to it. Anions and cations must be added in equal amounts to create salt. The valence factor for salts is the total number of positive or negative charges that a mole of salt provides.

  1. Origin of Equivalent Concept

Initially, 1 gram of hydrogen was added to the weight of an element to determine its equivalent weight. The definition was subsequently changed to read as follows: the equivalent weight of an element is the weight of the element plus 8 grams of oxygen. Note: Depending on the charge on an element, it may have more than one equivalent weight.

  1. Equivalent Volume of Gases

An equivalent volume of gas is the volume occupied by 1 equivalent of a gas at STP.

Equivalent mass of gas= molecular mass/Z

  1. Normality

Normality Volume provides the number of equivalents of solute present in a solution (L). The number of equivalents of the solute is conserved upon dilution of the solution, allowing us to use the following formula: 


Note : For the conservation of the equivalent number, this is the dilution equation. Since one equivalent of one reactant always reacts with one equivalent of another reactant, similar equations are used for acid and base titration problems. The same logic should not be applied to molarity. 

The relationship between Normality and Molarity is given by: N=M×Z; where ‘Z’ is the Valency factor

CBSE Class 11 Chemistry Notes Chapter 1 – Some Basic Concepts of Chemistry

Some Basic Concepts of Chemistry Class 11

Chapter 1: Some Basic Concepts of Chemistry Class

For Chemistry students to understand and advance, this chapter is crucial. These notes for Class 12 Chemistry are a top resource for preparing for board exams as well as competitive exams. Thus, reading these notes is crucial before any exams.

Some Basic Concepts of Chemistry Class 11 Notes – Free Download

Class 11 Chemistry Chapter 1 Notes focus on giving an introduction to the fundamental ideas of Chemistry in a clear and understandable manner. The Class 11 Chemistry Chapter 1 Notes are comprehensive and presented precisely to support better learning.

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