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What were the limitations of Dobereiner’s classification?
Limitation of Dobereiner’s Classification: Only few elements can be arranged in the Dobereiner's traids. It depends on their properties. F, Cl, Br will not show the traids but Cl , Br, I will show.
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Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Gallium and Scandium
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What were the criteria used by Mendeleev in creating his Periodic Table?
Mendeleev’s periodic table was based on the atomic masses of the elements. The properties of the elements are the periodic function of their atomic masses. Elements are arranged in the increasing atomic mass and their properties get reoccur after regular intervals
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Name (a) three elements that have a single electron in their outermost shells. (b) two elements that have two electrons in their outermost shells. (c) three elements with filled outermost shells.
(a) Lithium (Li), potassium (K) and rubidium (Rb) have a single electron in their outermost shells. (b) Barium (Ba) and calcium (Ca) have two electrons in their outermost shells. (c) Neon (Ne), argon (Ar), and xenon (Xe) elements have filled outermost shells.
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Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as (a) Na (b) Mg (c) Al (d) Si
(b) Valency of X in the given compound is 2. Mg is in the group 2 in the Periodic Table.
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