What Is Everything Made Of?
Two civilisations, one question.
Over two thousand years ago thinkers in India and Greece were asking it independently.
↳ The question is older than any experiment.
📚 Chapter Learning Kit
Journey Inside the Atom · Class 9 Science
English 5 topics 260 leveled MCQs 110 flashcards 4 games Free
Shared by a Veda teacher · Generated with Veda AI · Oct 2026
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Kanada's Parmanu
Divide matter far enough.
Dividing dravya again and again reaches particles that divide no further: parmanus, set down in the Vaisesika Sutras.
↳ Infinitely small, and beyond the senses.
No Proportions Given
What the old account left out.
It never says in what proportions parmanus combine to make one substance rather than another.
↳ A gap that experiment would later have to fill.
Bohr, 1913
Rescuing the atom from collapse.
A new model, proposed for the express purpose of explaining why atoms are stable.
↳ The previous model had them spiralling inward.
Fixed Circular Paths
Not anywhere they please.
Electrons keep to fixed paths called stationary states, orbits or shells.
↳ Never in the space between two shells.
K L M N, or 1 2 3 4
Two ways to name them.
↳ Farther out, higher up.
📖 Smart notes
What you'll study, topic by topic
1
Early Atomic Ideas, Thomson's Model and the Gold Foil Experiment
The atom began as a guess in ancient India and Greece, became a scientific theory with Dalton, and then stopped being indivisible altogether. A beam of alpha particles fired at gold foil demolished one model and put the…
- Over two thousand years ago thinkers in India and Greece were asking the same question about what everything is made of.
- Acharya Kanada held that dividing matter, or dravya, again and again brings you to particles that will divide no further, which he named par…
- A parmanu is infinitely small and beyond the reach of the senses, and parmanus join in twos and threes, dyads and triads, out of which the w…
~45 min · full explanation, examples & memory tricks in the app
2
Bohr's Shells, the Neutron, and the Symbols of Elements
Bohr rescued the atom from collapse by fixing electrons into allowed shells. Chadwick then found the uncharged particle that makes helium four times heavier than hydrogen rather than twice. And a short set of rules turne…
- Niels Bohr put forward a new model in 1913 for the express purpose of explaining why atoms do not collapse.
- In his account electrons do not wander about the nucleus at random but keep to fixed circular paths, which go by the names stationary states…
- In each shell an electron holds a definite quantity of energy, which is why the shells are also spoken of as energy levels.
~45 min · full explanation, examples & memory tricks in the app
3
Atomic Number, Mass Number and the Standard Notation
Two counts fix everything about an atom's identity and weight. The protons decide which element it is; the protons and neutrons together decide what it weighs. Both are written into one compact symbol that every chemist…
- The atoms of one element are all alike but differ from the atoms of every other element, and what they differ in is the number of electrons…
- Count the protons in the nucleus of one of an element's atoms and that count is its atomic number, written $Z$.
- That number settles the identity of the element and its chemical behaviour, so two atoms with different atomic numbers belong to different e…
~40 min · full explanation, examples & memory tricks in the app
4
Filling the Shells: Electronic Configuration and Valency
Three rules from Bohr and Bury decide where every electron goes, and once you can write a configuration you can predict how the atom will react. The outermost shell is where all the chemistry happens, and the count of el…
- Bohr and Bury laid down the rules by which electrons are distributed among the different energy levels.
- The maximum number of electrons a shell can hold is given by the formula $2n^2$, where $n$ is the number of the shell.
- So the K shell with $n = 1$ holds $2 \times 1^2 = 2$ electrons, the L shell with $n = 2$ holds $2 \times 2^2 = 8$, and the M shell with…
~50 min · full explanation, examples & memory tricks in the app
5
Isotopes, Average Atomic Mass and Isobars
Dalton said every atom of an element is identical. He was wrong about the neutrons. Twin atoms of one element differ in mass but not in chemistry, which is why chlorine's atomic mass reads 35.5 although no chlorine atom…
- Dalton had held every atom of a given element to be a copy of every other, down to its mass.
- Scientists later found atoms of one element that share an atomic number $Z$, and so a proton count, yet carry different numbers of neutrons…
- These twin atoms, alike in atomic number but different in mass number, are called isotopes.
~50 min · full explanation, examples & memory tricks in the app
❓ Leveled MCQ practice
Try the smart MCQs from this kit
260 questions laddered from warm-up to topper-level, each with an explanation. A taste:
Acharya Kanada's name for the smallest indivisible particle of matter was:
Beginner
A atomos, a term of Greek origin instead
B dravya, which is his word for matter itself
C parmanu, recorded in the Vaisesika Sutras
D dyad, which is a group of two such particles
Show answer & explanation
parmanu, recorded in the Vaisesika Sutras
Dravya is the matter being divided, not the particle.
The Greek word atomos means:
Beginner
A indivisible, which is what the particles were thought to be
B invisible, since the particles could not be seen
C immortal, since the particles never decay
D immense, describing the universe they build
Show answer & explanation
indivisible, which is what the particles were thought to be
Leucippus and Democritus proposed the idea.
The concept of the atom originated as:
Beginner
A a conclusion drawn from careful measurement
B an accidental discovery in a laboratory
C a prediction from a mathematical theory
D an imaginary idea rather than an experimental result
Show answer & explanation
an imaginary idea rather than an experimental result
Dalton's theory of 1808 was the first scientific account.
John Dalton proposed his atomic theory in the year:
Beginner
A 1897
B 1911
C 1808
D 1913
Show answer & explanation
1808
The other three years belong to later discoveries.
🃏 Flashcards
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