What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev’s Periodic Law.

Options

A.
B.
C.
D.

Explanation

**Step-by-Step Solution:**

1. **Identify the Physical Properties Used by Mendeleev:**
- Mendeleev primarily used **atomic mass** as a physical property to arrange the elements in his periodic table. He believed that the properties of elements are a periodic function of their atomic masses.

2. **Identify the Chemical Properties Used by Mendeleev:**
- For the chemical properties, Mendeleev considered the **nature and formula of oxides and hydrides** formed by the elements. This helped him classify elements based on their reactivity and similarities in chemical behavior.

3. **List Two Observations that Challenged Mendeleev’s Periodic Law:**
- **First Observation:** The increasing order of atomic masses could not be maintained while matching the chemical properties of the elements. For example, cobalt (Co) and nickel (Ni) have atomic masses that do not align with their chemical properties when arranged in order.
- **Second Observation:** Mendeleev's periodic table did not adequately account for **isotopes**. Isotopes are atoms of the same element with different masses, and Mendeleev's arrangement did not provide a clear position for them, leading to inconsistencies.

**Summary of the Solution:**
Mendeleev used atomic mass as a physical property and the nature of oxides and hydrides as chemical properties to create his periodic table. However, challenges arose due to the inability to maintain increasing atomic mass while aligning chemical properties (e.g., cobalt and nickel) and the lack of a clear position for isotopes.

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