Apr 28, 2025
# Chemistry: Understanding the Atom
## Structure of the Atom
- **Nucleus**: The center of the atom
- Contains protons and neutrons
- **Proton**: Positively charged (+1), relative mass 1
- **Neutron**: Neutrally charged, relative mass 1
- **Electron**: Orbits the nucleus in shells
- About 2000 times smaller than protons/neutrons
- Negatively charged (-1)
## Periodic Table
- Each element is represented by a box (nuclear symbol)
- **Element Symbol**: A short form, such as Li for Lithium
- **Atomic Number**: Number of protons (determines the element)
- Example: Lithium (Li) has 3 protons
- **Mass Number**: Total number of protons and neutrons
- Example: Lithium (Li) has a mass number of 7 (3 protons + 4 neutrons)
- Note: In a neutral atom, the number of electrons equals the number of protons
## Isotopes
- Atoms with the same number of protons but different numbers of neutrons
- Different mass numbers due to different neutrons
- Example: Lithium Isotopes
- Lithium-7 (3 protons, 4 neutrons)
- Lithium-6 (3 protons, 3 neutrons)
- Lithium-8 (3 protons, 5 neutrons)
- Stability of isotopes varies:
- Some are stable
- Unstable isotopes decay by emitting radiation (alpha, beta, gamma) or neutrons
- This process is known as radioactive decay
## Electron Energy Levels
- Electrons are arranged in shells (energy levels)
- Outer shells have more energy than inner shells
- Electrons can move between these levels:
- **Excitation**: Electron gains enough energy to move to a higher energy level
- Energy is gained from electromagnetic waves
- Electron falls back by re-emitting energy as waves
## Ionization
- Occurs when outer electrons absorb enough energy to leave the atom
- Results in the atom having more protons than electrons, creating a positive charge
- Such an atom is called a positive ion
- **Ionizing Radiation**: Capable of removing electrons from atoms to ionize them
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### Conclusion
This document reviewed the fundamental concepts of atomic structure, isotopes, electron energetic transitions, and ionization. Understanding these basics is crucial for the study and application of chemistry.