Structure of the Atom Class 9 Science — Revision Notes
This chapter explores atomic structure including nucleus and electron shells. Students learn about Rutherfords model, Bohrs model, and the arrangement of e
TL;DR: This chapter explores atomic structure including nucleus and electron shells. Students learn about Rutherfords model, Bohrs model, and the arrangement…
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This chapter explores atomic structure including nucleus and electron shells. Students learn about Rutherfords model, Bohrs model, and the arrangement of e
Subatomic Particles
- Proton: positively charged, in nucleus, relative mass 1
- Neutron: no charge, in nucleus, relative mass 1
- Electron: negatively charged, in orbits, relative mass 1/1836
- Atom is neutral when number of protons equals electrons
Rutherfords Model
- Nucleus is dense, positively charged center of atom
- Electrons revolve around nucleus in orbits
- Most of atom is empty space
- Explains scattering of alpha particles in gold foil experiment
Bohrs Model
- Electrons exist in fixed energy shells around nucleus
- Electrons cannot exist between shells
- Electron jumping absorbs or releases specific energy (photon)
- Explains line spectrum of hydrogen
Electron Distribution
- K shell: maximum 2 electrons
- L shell: maximum 8 electrons
- M shell: maximum 18 electrons
- Electrons fill inner shells first
- Valence electrons: electrons in outermost shell determine chemical properties
Key Terms
- Nucleus: Dense central region of atom containing protons and neutrons
- Valence Electrons: Electrons in outermost shell determining chemical properties
- Atomic Number: Number of protons in nucleus (defines element identity)
Frequently Asked Questions
How many protons are in nitrogen atom?
Nitrogen has atomic number 7, so it has 7 protons. A neutral nitrogen atom also has 7 electrons.
What is mass number of atom?
Mass number = number of protons + number of neutrons. It represents total number of subatomic particles in nucleus.
More Class 9 Science Revision Notes
- Matter in Our Surroundings
- Is Matter Around Us Pure
- Atoms and Molecules
- The Fundamental Unit of Life
- Tissues
- Motion
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