The key difference between Mendeleev's and Moseley's periodic laws lies in the basis for arranging elements in the periodic table. According to the provided reference [C], Mendeleev arranged elements in descending order according to atomic masses, while Moseley arranged them in descending order based on atomic numbers.
Here's a more detailed breakdown:
Mendeleev's Periodic Law
- Arrangement Principle: Dmitri Mendeleev arranged elements primarily by increasing atomic weight (also referred to as atomic mass).
- Periodic Law (Mendeleev's version): The properties of elements are periodic functions of their atomic weights.
- Limitations: Mendeleev's table had some inconsistencies. Some elements were out of order based on their properties because their atomic weights didn't perfectly align with their chemical behavior.
Moseley's Periodic Law
- Arrangement Principle: Henry Moseley, through his experiments with X-ray spectra, determined the atomic number (number of protons) of elements. He then arranged the elements by increasing atomic number.
- Periodic Law (Moseley's version): The properties of elements are periodic functions of their atomic numbers.
- Advantages: Moseley's arrangement resolved the inconsistencies present in Mendeleev's table. Elements fell into the correct groups based on their properties when arranged by atomic number. This provided a much more accurate and fundamental basis for the periodic table.
Summary Table
| Feature | Mendeleev's Periodic Law | Moseley's Periodic Law |
|---|---|---|
| Arrangement | By increasing atomic mass | By increasing atomic number |
| Basis | Atomic weight | Atomic number |
| Accuracy | Some inconsistencies | Resolved inconsistencies; more accurate |
| Periodic Law | Properties are a function of atomic weight | Properties are a function of atomic number |
In essence, Moseley's work refined Mendeleev's original concept by providing a more fundamental and accurate way to organize the elements, establishing atomic number as the true basis for periodicity.
