sci_phy
The Atomic Model
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
Free online summary and notes (ICSE Class 10 Hindi). Read it here, no PDF download needed.
About the author
Physics · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
His cathode-ray experiments (1897) revealed the tiny negative electron. The atom was thought to be a uniform positive 'dough' with electrons embedded in it.
Most alphas passed straight through; a few bounced back. That rebound could only come from a concentrated positive nucleus at the centre.
This fixed the stability problem and explained line spectra: each line is one specific energy jump, with photon energy E = h f.
Quantum mechanics replaced fixed orbits with orbitals (probability regions). For school physics: tiny positive nucleus, electrons in energy levels.
Hard words & meanings
| nucleus | the tiny, dense, positively charged centre of an atom holding protons and neutrons |
| proton | a positively charged particle in the nucleus, mass about 1 u |
| neutron | an uncharged particle in the nucleus, mass about 1 u |
| electron | a light, negatively charged particle that orbits the nucleus in shells |
| atomic number | the number of protons in an atom, which decides the element, symbol Z |
| mass number | the total number of protons and neutrons in the nucleus, symbol A |
| isotope | an atom with the same atomic number but a different mass number (different neutrons) |
| alpha particle | a positively charged particle (two protons + two neutrons) used to probe the atom |
Model exam answers, grammar & audio
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