Properties Do Not Survive
Two gases make a liquid that puts out fire.
Hydrogen burns, oxygen feeds a fire, and water does neither.
↳ But the mass does survive, exactly.
📚 Chapter Learning Kit
Atomic Foundations of Matter · 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
⚡ Veda Bites
💡 Key Idea
⚙️ Process
✏️ Example
📖 Definition
💡 Key Idea
✏️ Example
The whole idea, one bite at a time
Veda Bites are swipeable micro-lessons — each one teaches exactly one idea. Here's a taste from this kit; the app has the full deck.
Salt Into Water
Start with a physical change.
↳ No change in mass, as in every physical change.
A Sheet of Paper
The same point, torn up.
Weigh it, tear it into pieces, weigh the pieces. Nothing has changed.
↳ Physical changes do not touch mass.
What a Postulate Is
Not a proof. A starting point.
A starting assumption taken as true with nothing proving it, on which everything else is built.
↳ Its worth lies in what it explains.
Dalton's Postulates
The six, in order.
↳ Two explain conservation; two explain proportion.
Magnesium in Air
A white powder appears.
Magnesium oxide forms, showing magnesium atoms have combined with oxygen atoms.
↳ Nothing was destroyed; things were joined.
📖 Smart notes
What you'll study, topic by topic
1
The Law of Conservation of Mass and the Law of Constant Proportions
Weigh a reaction before and after and the balance does not move, provided nothing escapes. Analyse a compound from any source whatever and the elements in it always sit in the same ratio by mass. Two laws, and between th…
- Many properties of elements are not retained when they form a compound: hydrogen and oxygen are gases, while the water they form is a liquid…
- Hydrogen gas is combustible and oxygen supports combustion, yet water neither burns nor helps burning, and in fact puts out fire.
- For all that, weigh the water and you get back exactly what the hydrogen and the oxygen weighed between them before they joined.
~45 min · full explanation, examples & memory tricks in the app
2
Dalton's Postulates, Covalent Bonds and Naming Covalent Compounds
Six postulates explain both laws at a stroke. Then atoms get to work: an unfinished valence shell is completed by sharing, one pair at a time, and the shared pair is the bond. A prefix system turns the resulting molecule…
- A postulate is a starting assumption taken as true although nothing has formally proved it, and everything else in a theory is then built on…
- Dalton's postulates combined the experimental observations of his day and became the basis of modern scientific theory.
- First postulate: everything material consists of exceedingly small particles, named atoms, and it is these that take part when substances re…
~50 min · full explanation, examples & memory tricks in the app
3
Ionic Bonds, Ions and Naming Ionic Compounds
Where sharing will not serve, electrons change hands outright. One atom is left short and positive, the other over-supplied and negative, and the pull between the two is the bond. Such compounds do not stay as single uni…
- An atom whose valence shell holds fewer than four electrons will generally donate them in order to reach a stable electronic configuration.
- An atom with more than four valence electrons usually gains or shares electrons instead, so as to complete an octet.
- Sodium has atomic number 11 and only one electron in its valence shell, which it can shed to become stable.
~45 min · full explanation, examples & memory tricks in the app
4
Writing Chemical Formulae by the Criss-Cross Method
There is a faster route to a formula than counting electrons each time. Write the symbols, write the valencies under them, cross them over as subscripts, and reduce. Brackets and one small division rule are all that rema…
- Formulae can be written by finding the number of electrons shared or transferred, but there is a quicker route.
- For a covalent compound: first write the symbols of the constituent elements.
- Second, write the valencies of those elements underneath, taking them from the table of common ions where needed.
~45 min · full explanation, examples & memory tricks in the app
5
Properties of Ionic and Covalent Compounds, Molecular Mass and Formula Unit Mass
Put five substances into water, kerosene and petrol, then wire them to a bulb, and the two families sort themselves out. After that, adding up atomic masses gives the mass of a molecule, or of a formula unit where no mol…
- The activity uses samples such as camphor, sodium chloride, copper sulfate, sugar and naphthalene, testing each for solubility in water, ker…
- Safety first: do not touch the electrodes while they are connected to the battery, use a low voltage battery to avoid a shock, and take care…
- Two carbon or metal electrodes are fixed through holes in a piece of cardboard and connected to a 9 V battery and a bulb, and each sample is…
~45 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:
Which property does water share with neither hydrogen nor oxygen?
Beginner
A It puts out fires rather than burning or feeding them
B It is a gas at ordinary room temperature
C It is combustible when a flame is applied
D It supports the combustion of other substances
Show answer & explanation
It puts out fires rather than burning or feeding them
Properties do not survive the joining.
What happens to the mass when salt dissolves in water?
Beginner
A It falls, since the salt disappears from view
B It rises, since a new substance has formed
C It cannot be measured once dissolving begins
D It stays the same, as in every physical change
Show answer & explanation
It stays the same, as in every physical change
Tearing paper makes the same point.
Vinegar and baking soda react to give:
Beginner
A carbon dioxide and other substances
B oxygen and other substances
C hydrogen and other substances
D no products at all, merely a mixture
Show answer & explanation
carbon dioxide and other substances
The brisk effervescence is that gas leaving.
Why does the open flask give a final reading lower than the initial one?
Intermediate
A Some matter has genuinely been destroyed
B The balance loses accuracy during a reaction
C The vinegar evaporates completely away
D The gas produced escapes from the open flask
Show answer & explanation
The gas produced escapes from the open flask
The gas got away, not the mass.
🃏 Flashcards
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110 flashcards in this kit — the app reviews them with spaced repetition so the right card returns on the right day.
🎮 Learning games
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Word Match
True False
Fill Blank
Word Scramble
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