[Revision] Chemistry Part-1: Matter, Mass, Isotopes, Isobars,X-Ray, Alpha-Ray, Gamma-Ray, Cathode-Ray & More

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  1. Prologue
  2. Matter classification
  3. Properties of a Substance
  4. SI system of measurement
  5. 7 Basic units in SI measurement
  6. Definition of SI units
  7. Difference between Mass and weight
  8. Why Pt-IR cylinder for weight standardization?
  9. Temperature
  10. Five Laws of Chemical combination
  13. Cathode Ray Tube & Television
  14. X-Ray & Roentgen
  15. Atomic Mass
  16. Isotopes of Hydrogen
  17. Mole and Avogadro
  18. Atomic Models
  19. Quantum Mechanic Model
  20. Photoelectric Effect: Einstein & Planck
  21. Spectrum
  22. Electromagnetic spectrum
  23. Black Bodies
  24. Mock Questions


  • This year’s UPSC CAPF paper contained significant number of questions science, particularly higher level chemistry (Above class7-10 NCERTs)
  • In recent years, UPSC has been shifting from Class 7 to 10 Science NCERTs towards 11-12 NCERTS) – This has been evident in all 3 exams conducted by UPSC viz. CAPF, CDS and CSE-prelims.
  • Therefore, with help of Venkat sir, I’m preparing selected “revision notes” out of NCERT Science Books (11, 12).  Most important: can’t guarantee this project will be finished before prelim comes.
  • First part of this article series deals with Class11 Chemistry NCERT Chapter 1 (Basic concepts of matter) and chapter 2 (Structure of Atom).

Matter classification

Chemistry Matter Classification

Possible MCQ: Assertion reasoning, “which of the following 2-3 statements are correct?”

Properties of a Substance
physical properties chemical properties
  • they’re measured or observed without changing the identity of material- e.g. colour,  odour, melting point, boiling point, density
  • we can observe them only after chemical change occurs.
  • e.g. acidity or basicity, combustibility

SI system of measurement

  • Through Metre convention in Paris (1875), this International system of units was setup.
  • accordingly, each country has an institute to maintain standards of measurement
  • e.g. in India it is done by National physical laboratory @Delhi.

7 Basic units in SI measurement

NCERT-11-P1-SI basic

Possible MCQ: Macth the following

Definition of SI units

NCERT-11-P1-SI definition

Possible MCQ: Which of the following statements correct about xyz unit?

Difference between Mass and weight
A substance’s mass will remain same everywhereWill change depending on gravity of the given place.
Measured using “Analytical balance”measured using weighing scale

Why Pt-IR cylinder for weight standardization?

  • The Mass standard is kilogram.
  • Kilogram is defined as the mass of platinum-iridium (Pt-Ir) cylinder that is stored in an airtight jar at International Bureau of Weights and Measures in Sevres, France.
  • Pt-Ir was chosen for this standard because it is highly resistant to chemical attack and its mass will not change for an extremely long time.
  • Assertion reasoning question possible from above factoids
NCERT-11-P1-SI prefixes

Possible MCQ: Match the following prefix vs. multiple / convert “x” into “y”

°C (degree celsius)
  • calibrated from 0° to 100° where these two temperatures are the freezing point and the boiling point of water respective
  • Negative values possible in celcius
°F (degree fahrenheit)
  • fahrenheit scale is represented between 32° to 212°.
  • F = [9C/5]+32
K (kelvin)
  • K=C+273.1
  • Negative values not possible


Five Laws of Chemical combination
Law ofDetail
1.Conservation of Mass
  • matter can neither be created nor destroyed – Antoine Lavoisier (1789)
2.Definite Proportions
  • a given compound always contains exactly the same proportion of elements – Joseph Proust
  • E.g. both naturally occurring and artificially synthesized Cupric carbonate will have same elements in same ratio.
3.Multiple Proportions
  • if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers – Dalton
  • example 2 gm Hydrogen + 16 gm Oxygen = 18 gm water
  • but 2 gm Hydrogen + 32 gm Oxygen = 34 gm Hydrogen Peroxide.
4.Gaseous Volumes
  • Gay Lussac (1808)
  • When gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure.
  • If 100 ml hydrogen combine with 50 ml oxygen, we get 100 ml water vapour.
5.Avogadro Law
  • equal volumes of gases at the same temperature and pressure should contain equal number of molecules
  • He differentiated atoms from molecules.


  1. Democritus, a Greek Philosopher (460 — 370 BC) said that matter is composed of small indivisible particles called ‘a-tomio’ (meaning — indivisible). Indian philosophers also made similar statements. But they had no proofs.
  2. Finally, a British Teacher John Dalton published book published ‘A New System of Chemical Philosophy’ (1808) with following points
  3. Matter consists of indivisible atoms.
  4. All the atoms of a given element have identical properties and identical mass.
  5. Atoms of different elements differ in mass.
  6. Compounds are formed when atoms of different elements combine in a fixed ratio.
  7. Chemical reactions involve reorganisation of atoms. These are neither created nor destroyed in a chemical reaction.
his theory can explain following:

  • laws of chemical combination
  • law of conservation of mass
  • law of constant composition
  • law of multiple proportion
He couldn’t explain following

  • If glass or ebonite when rubbed with silk or fur, it’ll generate electricity.  Why?
  • Same way result of many experiments, he couldn’t explain.
Ascending descending order of weight / charge could be asked in MCQ

Ascending descending order of weight / charge could be asked in MCQ

Discovery ofWas discovered by
1.ElectronA cathode ray discharge tube – cathode ray particles – observed though fluorescent or phosphorescent – negatively charged particles, called electrons
2.Protonmodified cathode ray tube – canal rays – positively charged particles
3.NeutronChadwick (1932). he bombarded alpha-particles on beryllium thin sheet.

Cathode Ray Tube & Television

  • 1830: Michael Faraday showed that if electricity is passed through a solution of an electrolyte, matter will be liberated and deposited at the electrodes.  (1830)
  • 1850s: Faraday began to study electrical discharge in cathode ray tubes
  • A cathode ray tube is a sealed glass tube containing two thin metal pieces (electrodes).
  • Cathode rays start from cathode and move towards the anode.
  • Cathode ray will travel in straight line IF there is no electrical or magnetic field,
  • If there is electrical/magnetic field, cathode rays will behave like charged particles.
  • Characteristics of cathode rays (electrons) do not depend upon (1) the material of electrodes (2) nature of the gas present in the cathode ray tube.
  • Cathode rays themselves are not visible but their behaviour can be observed with the help of certain kind of materials (fluorescent or phosphorescent) which glow when hit by them.
  • We can observe electrical discharge through the gases only at very low pressures and at very high voltages.
  • Television picture tubes are cathode ray tubes
  • Television pictures result due to fluorescence on the television screen coated with certain fluorescent or phosphorescent materials.

X-Ray & Roentgen

  • Wilhalm Röentgen: strike electron to dense anode metal in Cathode ray tube => rays produced => these rays cause fluorescence in the fluorescent materials placed outside the cathode ray tubes. He called them X-Rays (1895)
  • Henri Becqueral coined the term radioactivity. Marie Curie, Piere Curie, Rutherford and Fredrick Soddy worked further in this field.
Alpha particles1
  • Alpha particles are Positive charged.
  • Alpha particle + 2 electron = helium
  • Rutherford bombarded very thin gold foil with alpha–particles but most of the a– particles passed through the gold foil undeflected.
  • Thus he provide Most of the space in the atom is empty. And volume occupied by the nucleus is negligibly small as compared to the total volume of the atom.
Beta Rays100 x alphanegatively charged particles similar to electrons
Gamma-Rays1000 x alpha
  • neutral in nature
  • don’t have any particles.

Atomic Mass

  • Greek word ‘stoichiometry’ =stoicheion (meaning element) + metron (meaning measure).
  • Stoichiometry calculation of masses and volumes of reactants and products of a chemical reaction.
  • 19th Century scientists assigned mass of “1” to Hydrogen. (no units, only number). All the remaining elements were given mass number relative to Hydrogen.
  • 1961: Carbon – 12 isotop is assigned a mass of exactly 12 atomic mass unit (amu) and masses of all other atoms are given relative to this standard.
  • Thus, One atomic mass unit (AMU) = one- twelfth the mass of one carbon – 12 atom.
  • Today, ‘amu’ has been replaced by ‘u’ which is known as unified mass.
  • Today, we have sophisticated techniques e.g., mass spectrometry for determining the atomic masses fairly accurately.
What’s the difference between
Atomic number (Z)Mass Number (A)
  • total protons = Z
  • total electrons =Z
  • Proton + neutron = nucleons.
  • total nucleons = A
  • Z written in subscript below the element symbol, on left side.
  • A written in superscript above element symbol, on left side.
  • Isotopes= same “Z” but different “A”. means Isotopes have same number of protons but different number of neutrons.
Isobars= same “A” but different “Z”


Misc. Definitions
Average Atomic Mass
  • If an element has more than one isotope
  • Its Avg. atomic mass = weighted average of (atomic mass x its relative occurrence in percentages)
Formula Masse.g. formula mass of sodium chloride = atomic mass of sodium + atomic mass of chlorine


Isotopes of Hydrogen
protium1099.985% hydrogen is like this
tritium12trace amount in earth
  • Similarly Carbon has 3 isotopes, chlorine has 2 isotopes
  • An Element’s chemical property depends on no. of electrons, and not much on neutrons. Therefore, Isotopes show same chemical behaviour. (can be asked for assertion-reasoning)

Mole and Avogadro

  • One mole = Amount of a substance that contains as many particles as there are atoms in exactly 12 g (or 0.012 kg) of the Carbon 12 isotope.
  • 1 mol is also known as ‘Avogadro’ constant, in honour of Amedeo Avogadro. It equals to 6.022×1023 atoms

Atomic Models

  • also known as plum pudding, raisin pudding or watermelon model (1904)
  • he said atom possesses a spherical shape (radius approximately 10 –10 m) in which the positive charge is uniformly distributed.
  • The electrons are embedded into it in such a manner as to give the most stable electrostatic arrangement
  • He got Nobel Physics for discovering how gases conduct electricity. (1906)
  • Atom resembles the solar system, nucleus is the Sun, and electrons are revolving planets.
  • Electrons and the nucleus are held together by electrostatic forces of attraction
  • he failed to explain stability of an atom.
  • it says nothing about the electronic structure of atoms i.e., how the electrons are distributed around the nucleus and what are the energies of these electrons.
3.NEILS BOHR, Denmark
  • Orbit is a circulate path around nucleus. Electrons move only in Orbit.
  • He was the first to explain quantitatively the general features of hydrogen atom structure and its spectrum. Though the theory is not the modern quantum mechanics.
  • He could not explain how atoms form molecules by chemical bonds. Hence Max Plank, Schrödinger et al began towards Quantum theory.
  • James Maxwell: discussed electromagnetic radiation.
  • Post WW-1, Bohr worked for peaceful uses of atomic energy, got Nobel in 1922.
4.Wolfgang Pauli, Austria
  • No two electrons in an atom can have the same set of four quantum numbers.
  • Only two electrons may exist in the same orbital and these electrons must have opposite spin.
  • Oil drop experiment to measure charge of electrons.

Quantum Mechanic Model

  • Classical atomic models ignore dual behavior of particles.
  • Just like radiation, particles also have dual properties i.e. Wave like properties and particle like properties (French physicist, de Broglie in 1924).
  • This is known as “Quantum mechanics”- Erwin Schrödinger – Nobel winner Austrian physicist was the front runner of this theoretical science.
  • We can’t find the exact position and exact momentum (or velocity) of an electron at the same time, because electron and other similar particles don’t have definite paths or trajectories of electrons and other similar particles- This is Heisenberg’s Uncertainty Principle.
  • Heisenberg was a German who shared Nobel with Schrödinger in Physics. He researched atomic bomb for Germany during WW2
  • Electrons wave-like properties are utilized in electron microscope, it can give a magnification of about 15 million times.

Photoelectric Effect: Einstein & Planck

German physicist Max Planck observed that:

  • When Light strikes surface = electrons ejected without any time lag.
  • How many electrons ejected? Ans. Proportional to light’s brightness.
  • How much is the kinetic energy of these ejected electrons? Ans. NOT in proportion of light’s brightness.
  • If red light shined on potassium for hours but no photoelectrons are ejected.
  • But even if a very weak yellow light shines on the potassium metal, the photoelectric effect is observed.
  • German born American physicist Albert Einstein was able to explain this Photoelectric effect using Planck’s quantum theory of electromagnetic radiation.
  • Einstein said light shining = shooting photon particle beam =collision with electrons=electrons ejected.
  • Brighter light = more protons = more electrons ejected.
  • He Won Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect.


  • Speed of light depends upon the nature of the medium through which it passes.
  • As a result, the beam of light is deviated or refracted from its original path as it passes from one medium to another.
  • The light of red colour which has longest wavelength is deviated the least while the violet light, which has shortest wavelength is deviated the most.
  • Examples of continuous spectrum:  (1) White light spectrum (2) rainbow. Because they have all colors from violet to red.
  • The study of emission or absorption spectra is referred to as spectroscopy
Electromegnetic Spectrum

Possible MCQ: ascending descending order of rays depending on thier frequencies / their utility

Electromagnetic spectrum

  • Water wave and sound wave need medium. They can’t move in vaccum
  • Electromagnetic waves do not require medium and can move in vacuum.
  • There are many types of electromagnetic radiation depending on their wavelength (or frequency).
  • Collectively, they’re called electromagnetic spectrum
What’s the difference?
  • Distance between two successive crests (or troughts)
  • SI unit is units of length is meter (m).
  • Wave number = Wavelengths per unit length. Unit is 1/m.
  • frequency is the number of waves that pass a given point in one second
  • SI unit is Hz, named after Heinrich Hertz

Black Bodies

Wave nature of Electromagnetic radiation can explain following:

Diffractionit is the bending of wave around an obstacle
Interferenceit is the combination of two waves of the same or different frequencies to give a wave
  • But above things can’t explain a black body radiation. Later Max Planck explained it in following manner:
  • When solids are heated they emit radiation over a wide range of wavelengths.
  • Heating Iron rod = dull red (low frequency) => more heating => bright red color (higher frequency)=>more heating=> white=>Blue…frequency keeps on increasing, wavelength keeps on decreasing.
  • Black body is the ideal body that emits and absorbs all frequencies.
  • The radiation emitted by such a body is called black body radiation.
  • Black Body’s radiation depends only on its temperature….At a given temperature, intensity of radiation emitted increases with decrease of wavelength, reaches a maximum value at a given wavelength and then starts decreasing with further decrease of wavelength (something like a bell curve).
  • Planck suggested that atoms and molecules could emit (or absorb) energy only in discrete quantities and not in a continuous manner. This smallest energy quantity is “quantum”.

Mug up following drugs because given in class11 Chemistry NCERT

Cisplatin, TaxolCancer
AZT: AzidothymidineAIDS

Mock Questions

Following type of MCQs can be framed:

  1. Whatever “cause-consequence” or “x because of y” type of information is given in this note, it can be utilized for assertion reasoning questions e.g. (1) why Pt-IR used in weight std. (2) how cathode-ray works in TV
  2. Match the following (1) scientist vs. principle. (2) basic physical quantity vs name of the SI unit (3) range of electromagnetic spectrum vs. utility of those rays (4) alpha, beta, gamma and x-rays vs their properties (similar qs. asked in CAPF) (5) isotopes of hydrogen vs. no. of neutrons present in them
  3. You can be given a term, and asked to identify the “factor responsible or variable attached.” example (1) Black body radiation depends on which of the following factors? (2) Cathode ray’s travel path depends on which of the following factors?
  4. 2 or 3 statements about Biography-contribution of Einstein- then you’re asked to identify the right or the wrong ones.
  5. Which of the following statements are correct about (1) Atomic mass / number (2) isotope vs. isobar (3) mass vs. weight and so on.

Mrunal recommends

  1. (free) NCERT, NIOS, TN-Books
  2. Environment by ShankarIAS
  3. Indian Polity M.Laxmikanth (Hindi | English)
  4. Art & Culture by Nitin Singhania (Hindi | English)
  5. Spectrum: Modern History (Hindi | English)
  6. Bipin Chandra: Post Independence
  7. Fast-track to Arithmetic Rajesh Verma
  8. MK Pandey’s Analytical Reasoning
  9. Disha’s Topicwise Paperset (Hindi | English)
  10. School Atlas
  11. Mains: Language papers
  1. (free) NCERT, NIOS, TN-Books 4 History,Geo,Sci
  2. Indian Polity M.Laxmikanth (Hindi | English)
  3. Spectrum: Modern History (Hindi | English)
  4. Maths: Quantam CAT Sarvesh Kumar
  5. Objective General English SP Bakshi
  6. Word Power made Easy -Norman Lowe
  7. Topic wise Solved Paperset by Disha

So far 45 Comments posted

  1. sathya

    atlast mrunalji is back 🙂

    1. csl80

      shhhh shhh sathya not fullly :-p

  2. satyajit

    Sir please reply what about lectures can we accept before pre

  3. infinite_quest

    How much important is matter, mass etc. for prelims? May we skip it? Rather may I ask for some help in culture?

  4. sachin

    UPSC prelims ya IIT Prelims?

  5. neeraj

    sir spipa cgrs bank cgl k ppt toh download kr liye h but vedios nhi mil rahi plz upload or provide me link

  6. sam

    more chemistry questions less chances for non science students for answering..

  7. saba

    Thnks a lot Mrunal Team for guiding and showing the current trend of upsc. Really very useful article and very very helpful in making right strategy at the last time. Do continue this endeavour Mrunal Sir. Thank u once again for analysing answerkes of CSE, CAPF, CDS and making us aware of upsc’s trend and correcting our strategy.

  8. sowjanya

    Thank u sir… waiting for economy lectrues..plz do post it sir

  9. Abhignu

    Sir, Is the economy lectures in SPIPA academy over. Last pillar of human resource is left to be posted.

  10. aspirant

    thats not upsc surely !! no laxmikant no bipin chandra no ncerts can slove these !! 🙁

  11. sam

    where is “spipa cgrs bank cgl k ppt” can you share the link

  12. sanju

    thanq sooo much sir….u r helping so many students….i donno hindi sir so i cant able to watch your economy lecture….so please post economy lect as soon as possible sir……..thank you sir

  13. Tirup Parmar

    Thank u so much Venkat sir and Mrunal sir…Really a very helpful article..Thanx a ton for helping us…:)

  14. H K A

    This is a great initiative. Kindly post the same for Biology 11th and 12th NCERT too. Much needed! Thanks a lot.

  15. Harshwardhan

    very helpful for working professionals. if possible ,kindly do the same for economy …

  16. mnemonic

    mnemonic for spectrum from IR is IMFL (indian manufactured foreign liquor) – (IR , Microwave , FM,AM,Long Radio Waves)

  17. Rhea

    Mrunal Sir, Please, please try and finish it before the pre. As someone from a non-technical background 11th and 12th NCERT science is way too challenging! Will there be a physics and biology series also 😛

  18. Bhavana

    Can you please post Rajatanil mam’s interview ? You and Mam are a real source of inspiration, motivation and strength for millions of aspirants like me.

  19. Aryan Raj

    Matter classification

    Image >> Point 8 >> They Can’t ??

  20. Bahubali

    Chemistry at this level of difficulty.? UPSC kya bachho ki jaan legi ab..?

  21. Aniket

    You Wrote ”Brighter light = more protons = more electrons ejected.”

    Its More photon == more electrons ejected, not protons 😛

  22. Anxious

    Sir, if you’re reading this, it is highly appreciative of you to be doing this however given the time constraint, if you do plan on continuing this further, a humble suggestion would be [following your scheme of plans and the cost-benefit ratio] chapter 14 of NCERT 11 and 14,16 of NCERT 12. I think that’ll be better for aspirants to do quick revision. I observed the word ‘selected’ on your heading and i think it’ll save time and energy for you and your colleague too, if other topics are left aside. Just my opinion.

    1. Manish

      Agreed! Sir it’d be great if you could consider this suggestion.

  23. Robin

    Thank you for this upload Sir. Chemistry revise ho raha hai .. Awaiting more of such uploads. And will u upload physics too?

  24. govindan

    Thank God our Mrunalji is back.

    We do sincerely request him to post articles / essays / notes on current economic topics like ‘one rank one pension’ which was asked in SBI Mains Exam, “climate change / climate adaptation / climate fund / and all aspects of climate, its adverse effects on the world, measures being taken by India and other country to save the earth etc., Monetary policy – current controversy between MoF and RBI, what is ideal, why? etc etc for the benefit of lakhs of RBI aspirants and civil service aspirants

    We also wish him good health, happiness and prospertiy

  25. Deeksha

    Done ooo done …..team good format presenting

  26. shweta

    thank you sir ..though I am a late follower but will catch up ..good level of study material n mock questions on diff subjects. thank u once again.
    one thing I l add is that our PM has added to our preparation while being workaholic…more visits , more agreements, more e governance projects, phewwwww!!!


    Thanks sir for making life easier! 🙂

  28. Saket

    Hello Sir!

    1- I have been following your Economy Series(Youtube). I am confident that the pending HRD related lectures gonna come. But time is
    ticking fast.Kindly post them as early as possible.If video not possible slides will do.

    2- Your current affairs files were awesome source to fine tune current affairs notes. Kindly post after May weak 2 onwards.

    Thanks 4 being Awesome!

  29. Good !!!

    Mrunal ji… Sir ji… HRD sections ok delay na karen… Please.

  30. Gurshi

    Perfect,..thanku so much mrunal team

  31. ubaid khan

    plz change proton to photon in paragraph Photoelectric Effect

  32. priti

    Sir i want total explnation of exam in Ssc crpf gd plzz

  33. rahul

    sir if not all then please try to cover biology part before pre.

  34. swaroop

    Hello Mrunal sir and Venkat sir,

    Thank you so much for wonderful article!!!


  35. Nandita

    Hello Mrunal,

    This is really really helpful..Please try to complete this chemistry potion before prelims. It will be highly valuable….


  36. Demos

    Thanks for this and please continue this type of articles and consolidated articles on other static or selective important current topics. No one does this better.

  37. prabhjeet

    thanks a lot sir i have clear all my doubts of eco and geo i have watched both subjects video u have saved a lot of time for students like us who are self learner i am going to give prelims 2015 exam as i am an mba student at jalandhar not having so much time just watched these videos clearly help me to cover my syllabusfor prelims sir i have opted for public administration guide me some god books regarding that.thanks a looooooooooooooooooooooooot for your contribution towards aspirants of ias. all the best to all for ias 2015

  38. sur

    thanks a lot sir!!

  39. Akshay

    Its too good .

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