๐ฐ Introduction
Elements are the basic building blocks of all substances. To make their study easier, scientists have classified them into groups based on similar properties. This chapter discusses how elements are arranged in the modern periodic table and the trends observed.
๐งช Need for Classification
In the early days, studying individual elements was difficult due to the large number.
Classification helps in predicting properties and behaviors of elements.
Early attempts include Dobereiner's Triads and Newlands' Law of Octaves.
๐ Mendeleev's Periodic Table
Based on atomic mass.
Elements arranged in increasing order of atomic mass.
Left gaps for undiscovered elements.
Placed elements with similar properties in the same column.
Limitations:
No fixed position for hydrogen.
No explanation for isotopes.
Irregular increase in atomic masses.
⚛️ Modern Periodic Table
Based on atomic number (number of protons).
Proposed by Henry Moseley.
Elements arranged in rows (periods) and columns (groups).
| Feature | Description |
|---|---|
| Periods | Horizontal rows (7 periods) |
| Groups | Vertical columns (18 groups) |
| Atomic Number | Increases from left to right |
| Properties | Repeat periodically |
๐ Trends in Modern Periodic Table
1. Valency
Increases from 1 to 4 and then decreases to 0 across a period.
Same in a group.
2. Atomic Size
Decreases across a period (left to right).
Increases down a group.
3. Metallic and Non-metallic Character
Metals: Found on the left and center. Metallic character decreases across a period.
Non-metals: Found on the right. Non-metallic character increases across a period.
Down a group, metallic character increases.
4. Electronegativity & Ionization Energy
Electronegativity and ionization energy increase across a period.
Decrease down a group.
๐งฌ Important Terms
Metalloids: Elements showing properties of both metals and non-metals (e.g., Si, As).
Noble Gases: Group 18, highly stable and inert.
Periodic Law: Properties of elements are a periodic function of their atomic numbers.
✅ Key Points to Remember
Modern periodic table is based on atomic number.
7 periods and 18 groups.
Predict trends like valency, size, metallic character, etc.
Classification helps simplify the study of elements.
No comments:
Post a Comment