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💡 Meet the proton
Before fixing the stability problem, scientists met another resident of the nucleus — a heavy, positive particle named the proton.
What is a proton?
Proton
A positively charged particle in the nucleus, much heavier than an electron, with equal and opposite charge.
- A positively charged particle in the nucleus .
- It is much heavier than an electron.
- Its charge is equal and opposite to that of an electron.
For an atom to be electrically neutral , the number of protons must equal the number of electrons. For example, helium has 2 protons and 2 electrons; sodium has 11 protons and 11 electrons.
⏸▶ Pause and Ponder
- 7. Assertion (A): Rutherford concluded most of the mass of an atom is at the centre (the nucleus). Reason (R): In Thomson’s model, electrons are embedded in a uniform positive sphere. Answer: (ii) Both A and R are true, but R is not the correct explanation of A. (A comes from the gold foil result; R just describes the older model.)
Important Definitions
- Proton — a positively charged particle in the nucleus with a charge equal and opposite to that of an electron.
