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Welcome to Class 11 Chemistry

Class 10 taught you what reactions happen. Class 11 asks how much, how fast to equilibrium, with how much energy — and why atoms bond the way they do.

1. Where Class 10 left you

In Class 10 you met chemistry as a set of reactions to recognise and describe: metals displacing hydrogen from acids, acids neutralising bases, carbon forming chains and rings, and equations that had to be balanced. You learned what happens.

Class 11 asks the questions that turn description into science. How much? — how many grams of product, how many particles, what concentration (the mole, Chapter 1). Why? — why atoms have the structure they do, why the periodic table repeats, why molecules have shapes (Chapters 2–4). Will it go, and how far? — energy, entropy and equilibrium (Chapters 5–6). Then the course returns to reactions with new eyes: electron transfer in redox (Chapter 7) and the logic of organic chemistry (Chapters 8–9).

📦 Class 10 ended with…

$$\mathrm{Zn(s)+H_{2}SO_{4}(aq)\rightarrow ZnSO_{4}(aq)+H_{2}(g)}$$ "Zinc reacts with dilute sulphuric acid to give hydrogen."

🚀 Class 11 begins with…

How many grams of zinc give $1.00\ \mathrm{L}$ of hydrogen? Which reactant runs out first? How much heat is released, and why is the reaction spontaneous?

2. A story that needs the whole course

About half of the nitrogen atoms in your body passed through a factory. Plants need nitrogen compounds to grow, and since the early twentieth century most of the world's fertiliser has come from ammonia made by the Haber process: $\mathrm{N_{2}(g)+3H_{2}(g)\rightleftharpoons2NH_{3}(g)}$. Roughly 180 million tonnes of ammonia are made each year, and without it the world could feed perhaps only half of today's population.

Every chapter of this course appears in that one equation. How many tonnes of ammonia does a tonne of nitrogen give? That is the mole (Ch. 1). Why is $\mathrm{N_{2}}$ so unreactive? Its triple bond, explained by molecular orbital theory (Ch. 4), built on atomic structure (Ch. 2) and periodicity (Ch. 3). The reaction releases heat — thermodynamics (Ch. 5) — so, by Le Chatelier's principle (Ch. 6), low temperature favours ammonia, yet the plant runs hot with an iron catalyst to make the reaction fast enough. Nitrogen goes from oxidation number $0$ to $-3$: a redox reaction (Ch. 7). The hydrogen comes mostly from methane, the simplest hydrocarbon (Ch. 9), and the fertiliser urea is an organic compound (Ch. 8).

✏️ Example 1 — A tonne of nitrogen
A plant converts $1.00$ tonne ($1.00\times10^{6}\ \mathrm{g}$) of $\mathrm{N_{2}}$ completely into ammonia. Using molar masses $\mathrm{N_{2}}=28.02$ and $\mathrm{NH_{3}}=17.03\ \mathrm{g\,mol^{-1}}$ and $\Delta_{r}H^{\circ}=-92.4\ \mathrm{kJ\,mol^{-1}}$ for $\mathrm{N_{2}(g)+3H_{2}(g)\rightarrow2NH_{3}(g)}$, find the mass of ammonia formed and the heat released.
Moles $n(\mathrm{N_{2}})=\dfrac{1.00\times10^{6}\ \mathrm{g}}{28.02\ \mathrm{g\,mol^{-1}}}=3.569\times10^{4}\ \mathrm{mol}$.
Equation $1\ \mathrm{mol}$ of $\mathrm{N_{2}}$ gives $2\ \mathrm{mol}$ of $\mathrm{NH_{3}}$, so $n(\mathrm{NH_{3}})=7.138\times10^{4}\ \mathrm{mol}$ and $m=7.138\times10^{4}\times17.03\ \mathrm{g}=1.22\times10^{6}\ \mathrm{g}=1.22$ tonnes.
Heat $\Delta_{r}H^{\circ}$ refers to one mole of reaction as written, i.e. one mole of $\mathrm{N_{2}}$: heat released $=3.569\times10^{4}\ \mathrm{mol}\times92.4\ \mathrm{kJ\,mol^{-1}}=3.30\times10^{6}\ \mathrm{kJ}$.
Check Mass is conserved: the extra $0.22$ t is the hydrogen ($3\times2.016=6.05\ \mathrm{g}$ per $28.02\ \mathrm{g}$ of $\mathrm{N_{2}}$, i.e. $0.216$ t). In a real plant only about 10–20% of the gas reacts in each pass because the reaction reaches equilibrium — Chapter 6 explains why the unreacted gas is recycled.
Interactive 1 — How Small Is a Molecule?

Shrink a cube of liquid water from $10\ \mathrm{cm}$ down to a fraction of a nanometre. The number of molecules inside is $N=\dfrac{\rho L^{3}}{M}N_{A}$ with $\rho=1.00\ \mathrm{g\,cm^{-3}}$ and $M=18.02\ \mathrm{g\,mol^{-1}}$. Only below about $4\ \mathrm{nm}$ are there few enough to draw; at about $0.31\ \mathrm{nm}$ the cube holds a single molecule.

1 cm
side $L$—
mass of water—
molecules $N$—
molecules along one edge—

3. The nine chapters at a glance

The course follows the current Class 11 syllabus in order. The textbook no longer has chapters on States of Matter, Hydrogen, the s- and p-Block Elements and Environmental Chemistry. The CBSE curriculum still keeps three of these topics for school assessment only (not the year-end board exam) — the gaseous state, the s-block, and the general trends of the p-block — and they are taught in 📘 boxes in Section 1.2 and Section 3.3. Where a later chapter needs a tool such as $pV=nRT$, it is also recalled briefly when needed.

1 · Mole concept→2 · Atom→3 · Periodicity→4 · Bonding→5 · Thermodynamics→6 · Equilibrium→7 · Redox→8 · Organic basics→9 · Hydrocarbons
Chapter 1

Some Basic Concepts of Chemistry

Measurement and significant figures, laws of combination, the mole, stoichiometry and concentration.

$n=\dfrac{m}{M}=\dfrac{N}{N_{A}}$
Open chapter → Chapter 2

Structure of Atom

Electrons, protons and neutrons; light and quanta; Bohr's model; orbitals, quantum numbers and configurations.

$E=h\nu$,   $\lambda=\dfrac{h}{mv}$
Open chapter → Chapter 3

Classification of Elements and Periodicity

From Mendeleev to the modern periodic law; s, p, d, f blocks; trends in radius, ionisation enthalpy and electronegativity.

properties = periodic function of $Z$
Open chapter → Chapter 4

Chemical Bonding and Molecular Structure

Lewis structures, VSEPR shapes, hybridisation, molecular orbitals and hydrogen bonding.

bond order $=\tfrac12(N_{b}-N_{a})$
Open chapter → Chapter 5

Thermodynamics

The first law, enthalpy and calorimetry, Hess's law, entropy and Gibbs energy.

$\Delta G=\Delta H-T\Delta S$
Open chapter → Chapter 6

Equilibrium

Equilibrium constants, Le Chatelier's principle, acids and bases, pH, buffers and solubility product.

$\mathrm{pH}=-\log[\mathrm{H^{+}}]$
Open chapter → Chapter 7

Redox Reactions

Oxidation numbers, balancing redox equations, titrations and electrode processes.

$\mathrm{Zn\rightarrow Zn^{2+}+2e^{-}}$
Open chapter → Chapter 8

Organic Chemistry – Basic Principles

Structural formulae, IUPAC names, isomerism, reaction mechanisms, purification and analysis.

$+I,\ -I,\ +R,\ -R$
Open chapter → Chapter 9

Hydrocarbons

Alkanes, alkenes, alkynes and aromatic hydrocarbons: preparation, reactions and mechanisms.

$\mathrm{C_{n}H_{2n+2}},\ \mathrm{C_{n}H_{2n}},\ \mathrm{C_{n}H_{2n-2}}$
Open chapter →
🗺️ How the chapters connect
  1. The mole (Ch. 1) is used everywhere — enthalpy per mole, concentrations in equilibrium constants, moles of electrons in redox, and the empirical formulae of organic compounds.
  2. Atoms → periodic table → bonds (Ch. 2–4). Electron configurations explain the shape of the periodic table, and the periodic trends explain which atoms share, give or take electrons.
  3. Energy and equilibrium (Ch. 5–6) answer "will it happen and how far?": $\Delta_{r}G^{\circ}=-RT\ln K$ ties the two chapters together.
  4. Redox (Ch. 7) applies electron bookkeeping from Chapters 2 and 4 and leads to electrochemistry in Class 12.
  5. Organic chemistry (Ch. 8–9) uses hybridisation and resonance from Chapter 4 to explain why reactions follow the paths they do.
🧭 How to use this course
  • Read with a pen. Try every worked example before opening its solution, then compare step by step. Always write units and watch significant figures.
  • Play with the labs. Each section has two interactives; change the settings until you can predict what will happen before you press ▶ Play.
  • Do the exercises in order. They run from routine to challenging, and every part has a full solution.
  • Use the 🎯 Exam corner. Every section ends with original problems in the style of the papers you will sit, tagged Board JEE Main JEE Advanced NEET, each with a full solution. Board problems stay strictly within the syllabus.
  • Know the two special boxes. A 🚀 Beyond the board syllabus box names the entrance exams that list its topic; board students may skip it. A 📘 school assessment only box teaches a topic that is in the CBSE syllabus and tested in school, but not in the year-end board exam.
  • Use the quiz as a gate. Five questions end every section; if you score below 4, reread before moving on. The Glossary and Formula Sheet collect everything in one place.

4. Prerequisite check — are you ready?

Eight quick questions on the Class 10 skills this course uses most. Answer all of them; for each one you miss you will see where the skill is needed, so you can revise it first.

Q1. Balance: $\mathrm{\_\,Al(s)+\_\,O_{2}(g)\rightarrow\_\,Al_{2}O_{3}(s)}$. The coefficients are
Q2. The formula of aluminium sulphate is
Q3. $0.00052$ in scientific notation is
Q4. $12\ \mathrm{g}$ of carbon burns completely in $32\ \mathrm{g}$ of oxygen. How much oxygen does $3.0\ \mathrm{g}$ of carbon need?
Q5. Rearranged for $V$, the formula $\rho=\dfrac{m}{V}$ becomes
Q6. A solution has $\mathrm{pH}=3$. It is
Q7. $10^{3}\times10^{-5}=$
Q8. Which is a chemical change?

When you are ready, start with Chapter 1 — Some Basic Concepts of Chemistry.

← Class 11 Chemistry — ContentsChapter 1 — Some Basic Concepts of Chemistry →