Answer:
Mendeleev categorized thallium (Tl) alongside lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs)
Explanation:
Characteristics of Thallium:
Thallium is a dense metal represented by the symbol Tl. It belongs to the 13th group and 6th period of the modern periodic table. The element is quite malleable and has a +3 oxidation state. It is rarely found in its elemental form in nature.
Mendeleev associated thallium with lithium and sodium because he observed that these elements, including Li and Na, form compounds with a single atom of chlorine (Cl), similar to the formation of TlCl by thallium (Tl). Thus, he classified Tl along with these similar elements.
Distinction of Thallium from the other five elements:
Unlike Li, Na, K, Rb, and Cs that exhibit a +1 oxidation state, Tl has a +3 oxidation state.
The color changed from white to red, which can only occur through a chemical reaction
