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Bot GPT-4o The periodic table is a systematic arrangement of the chemical elements, organized based on their atomic number, electron configurations, and recurring chemical properties. Key trends in the periodic table include:
1. **Atomic Radius**:
- **Across a Period (Left to Right)**: Atomic radius generally decreases because the addition of protons in the nucleus increases the positive charge, pulling the electrons closer.
- **Down a Group (Top to Bottom)**: Atomic radius increases as additional electron shells are added, making the atoms larger.
2. **Ionization Energy**:
- **Across a Period**: Ionization energy generally increases as atoms hold onto their electrons more tightly due to increasing nuclear charge.
- **Down a Group**: Ionization energy decreases because the outer electrons are farther from the nucleus and are shielded by inner electrons, making them easier to remove.
3. **Electronegativity**:
- **Across a Period**: Electronegativity usually increases. Elements are more eager to attract electrons to complete their valence shell.
- **Down a Group**: Electronegativity decreases. Higher atomic radius and shielding make it harder for the nucleus to attract electrons.
4. **Electron Affinity**:
- **Across a Period**: Electron affinity tends to become more negative (releasing more energy) as atoms are more likely to accept an additional electron to become more stable.
- **Down a Group**: Electron affinity becomes less negative. The added electron enters a higher energy level farther from the nucleus and is less tightly bound.
5. **Metallic and Non-metallic Character**:
- **Across a Period**: Metallic character decreases while non-metallic character increases as you move from left to right.
- **Down a Group**: Metallic character increases. Elements become more metallic as additional shells are provided, making it easier to lose electrons.
6. **Reactivity**:
- **For Metals**: Reactivity increases down a group (like alkali metals) because they can lose electrons more easily.
- **For Non-metals**: Reactivity decreases down a group (like halogens) because they gain electrons less readily due to increased atomic radius and shielding.
Understanding these trends helps predict the chemical behavior and properties of elements based on their position in the periodic table.