Structure of Atom 11 Chemistry — Revision Notes
The atom consists of a nucleus containing protons and neutrons, surrounded by electrons. Understanding atomic structure is essential for understanding chem
TL;DR: The atom consists of a nucleus containing protons and neutrons, surrounded by electrons. Understanding atomic structure is essential for understanding…
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The atom consists of a nucleus containing protons and neutrons, surrounded by electrons. Understanding atomic structure is essential for understanding chem
Subatomic Particles
- Proton has positive charge and resides in nucleus
- Neutron has no charge and resides in nucleus
- Electron has negative charge and revolves around nucleus
- Proton and neutron have nearly equal mass
- Electron mass is approximately 1/1836 of proton mass
Nuclear Atom Model
- Rutherford discovered that atom has dense nucleus with electrons around it
- Most of atom's mass is concentrated in the nucleus
- Nucleus is extremely small compared to overall atom size
- Electrons are attracted to nucleus by electrical force
- Electrons are in constant motion around nucleus
Bohr's Model of Atom
- Bohr proposed that electrons occupy specific energy levels or orbits
- Electrons can jump between orbits by absorbing or emitting energy
- First orbit holds maximum 2 electrons; second holds maximum 8
- Energy increases with distance from nucleus
- Model explains hydrogen atom spectrum but fails for larger atoms
Quantum Model of Atom
- Electrons exist in regions called orbitals with specific energy and shape
- Orbital is region where electron is likely to be found
- Probability of finding electron is shown by electron density
- Aufbau principle: electrons fill lowest energy orbitals first
- Pauli exclusion principle: no two electrons have identical quantum numbers
Electronic Configuration
- Electronic configuration shows arrangement of electrons in atoms
- Written as 1s2 2s2 2p6 3s2 3p6 for example
- Valence electrons are outermost electrons determining chemical properties
- Octet rule: atoms gain, lose, or share electrons to have 8 valence electrons
- Configuration determines element's position in periodic table
Key Terms
- Atom: Smallest unit of element that retains properties of element
- Nucleus: Central part of atom containing protons and neutrons
- Orbital: Region of space where electron is likely to be found
- Valence Electron: Electron in outermost shell that participates in chemical bonding
Frequently Asked Questions
Why does Bohr's model work for hydrogen but not for larger atoms?
Bohr's model assumes one electron, so it accurately predicts hydrogen's spectrum. For larger atoms with multiple electrons, electron-electron repulsion complicates the energy levels, making the model inaccurate.
What is an orbital and how is it different from an orbit?
An orbit is a fixed circular path where an electron moves, as proposed by Bohr. An orbital is a region where an electron is likely to be found, and has a specific shape and energy level.
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