The modern periodic table is more than just a chart — it’s a map of how elements behave and relate to each other. In this chapter, you will learn about the modern periodic table, trends in physical properties, how elements form compounds, and the special position of hydrogen. Understanding these concepts makes it easier to predict chemical reactions and is essential for exam success.
📥 Download Class 12 Chemistry Chapter 1 Notes
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❓ FAQ – Class 12 Chemistry Chapter 1
1. What is the main difference between Mendeleev’s and the modern periodic table?
- Mendeleev arranged elements by increasing atomic mass, whereas the modern periodic table arranges them by increasing atomic number, which resolves inconsistencies in properties.
2. What is the general trend of atomic radius in a period and a group?
- Across a period: Atomic radius decreases from left to right.
- Down a group: Atomic radius increases due to addition of electron shells.
3. Which elements are exceptions in the periodic trends of ionization energy?
- Beryllium (Be) and Nitrogen (N) show slightly higher ionization energy than expected due to stable electron configurations.
4. Why are halogens highly reactive?
- Halogens have 7 valence electrons and need only 1 electron to complete their octet, making them highly reactive, especially with metals.
5. How does electronegativity change across a period and down a group?
- Across a period: Electronegativity increases as atoms attract electrons more strongly.
- Down a group: Electronegativity decreases because outer electrons are farther from the nucleus.