Which important property did Mendeleev use to classify the elements in his periodic table and did he stick to that?

Answer

**Step-by-Step Solution:**

1. **Identify the Classification Basis:**
- Mendeleev used atomic weight as the primary property for classifying elements in his periodic table.

2. **Arrangement of Elements:**
- He arranged the elements in order of increasing atomic weights. This means that he listed the elements starting from the one with the lowest atomic weight to the one with the highest.

3. **Grouping by Similar Properties:**
- While arranging the elements, Mendeleev grouped together elements that exhibited similar chemical and physical properties. This was a crucial aspect of his classification system.

4. **Adherence to the Basis:**
- Mendeleev did stick to the basis of atomic weight for classification. He was consistent in using this criterion throughout his work.

5. **Inclusion of Unknown Elements:**
- Mendeleev left blank spaces in his periodic table for elements that were not yet discovered at the time. He predicted the existence of these elements based on the gaps in the table.

6. **Examples of Predicted Elements:**
- For instance, he predicted the existence of gallium and germanium. He referred to gallium as "eka-aluminium" and germanium as "eka-silicon" before they were discovered.

7. **Validation of Predictions:**
- When gallium and germanium were eventually discovered, their properties matched closely with Mendeleev's predictions, which validated his approach to classification.