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đź’ˇ A weighty mystery
A helium atom has 2 protons like “double hydrogen”, yet it is about 4 times heavier, not 2 times. Something extra must be sitting in the nucleus.
What are the three subatomic particles?
An atom
Made of three particles
1. Electron
Negative charge
Example:
Very light, outside nucleus
2. Proton
Positive charge
Example:
Heavy, inside the nucleus
3. Neutron
No charge
Example:
Heavy, inside the nucleus
Why is a helium atom heavier than expected?
- Helium has 2 protons (hydrogen has 1).
- By protons alone, helium should be about twice as heavy.
- But helium is about 4 times heavier — so the nucleus holds extra mass with no extra charge.
âť“ What if…
- What if an atom had no empty space at all?
- Almost all of an atom is actually empty space.
- Matter would then become unimaginably dense .
- Objects would shrink enormously in size.
NCERT Question 15 — In an atom, there are
In an atom, there are 12 protons and 12 neutrons in the nucleus. Now, imagine that all the electrons are replaced with some hypothetical particles that have the same charge as electrons but are 500 times heavier. What effect will this replacement have on the atom’s: (i) Atomic number (ii) Atomic mass (iii) Mass number (iv) Overall charge
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Important Definitions
- Mass of an atom — almost all of it is concentrated in the nucleus (protons and neutrons); electrons are too light to count.
