Structure of the Atom 9 Science — Revision Notes
Atoms contain subatomic particles—electrons, protons, and neutrons—arranged in a nucleus and electron shells with specific arrangements. Understanding atom
TL;DR: Atoms contain subatomic particles—electrons, protons, and neutrons—arranged in a nucleus and electron shells with specific arrangements. Understanding…
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Atoms contain subatomic particles—electrons, protons, and neutrons—arranged in a nucleus and electron shells with specific arrangements. Understanding atom
Discovery of Subatomic Particles
- Electrons: discovered by J.J. Thomson, negative charge, found in shells
- Protons: discovered by Rutherford, positive charge, located in nucleus
- Neutrons: discovered by Chadwick, neutral charge, located in nucleus
Atomic Models
- Thomson's model: plum pudding model with electrons embedded in positive sphere
- Rutherford's model: nucleus contains protons, electrons orbit in empty space
- Bohr's model: electrons in fixed orbits with specific energy levels, no intermediate energies possible
Nucleus and Atomic Structure
- Nucleus: dense center containing protons and neutrons
- Atomic number (Z): number of protons in nucleus, determines element identity
- Mass number (A): total protons plus neutrons
- Isotopes: atoms of same element with different neutron numbers
Electron Distribution
- Electrons occupy shells (K, L, M, N) with maximum electrons: 2n²
- K shell: 2 electrons max, L shell: 8 electrons max, M shell: 18 electrons max
- Valence electrons: outermost shell electrons, determine chemical bonding behavior
Key Terms
- Nucleus: Central part of atom containing protons and neutrons
- Atomic Number: Number of protons in an atom's nucleus
- Mass Number: Total number of protons and neutrons in nucleus
- Isotope: Atoms of same element with different number of neutrons
- Valence Electrons: Electrons in the outermost shell of an atom
- Electron Shell: Region around nucleus where electrons are found at specific energy levels
Frequently Asked Questions
Why does Bohr's model explain the line spectra of hydrogen better than Rutherford's?
Bohr's model assigns electrons to specific energy levels; transitions between levels produce characteristic frequencies of light.
How are isotopes of an element different?
Isotopes have same number of protons but different number of neutrons, resulting in different mass numbers.
What determines the chemical properties of an element?
The number of valence electrons (outermost shell electrons) determines an element's chemical properties and bonding behavior.
More 9 Science Revision Notes
- Matter in Our Surroundings
- Is Matter Around Us Pure
- Atoms and Molecules
- The Fundamental Unit of Life
- Force and Laws of Motion
- Work and Energy
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