Question

what are the main disadvantage of mendalee'v periodic table​

Answer 1

Answer:

1. Mendeleev could not arrange hydrogen properly because it shows the properties of both alkali metals and halogen. 2. Mendeleev could not arrange isotopes because they have different atomic weights but the same atomic number.

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Answer 2

Disadvantages of Mendeleev's Period Table :

Position of Hydrogen :

• The electronic configuration of hydrogen resembles with alkali metals.

• Moreover, it combines with halogen, oxygen and sulphur to give similar type of compounds as given by alkali metals.

• But just like halogen it exists in the atomic form and combined with metals and nonmetals to form covalent compounds.

• Thus, its position was not fixed in the Mendeleev's periodic table but it was kept with alkali metal.

Position of Isotopes :

• Isotopes of an element have similar chemical properties but different atomic masses.

• In Mendeleev's periodic table no place was given to these elements.

Uncertainty in Atomic Masses :

• Another problem was that the atomic masses do not increase in a regular manner in going from one element to the next.

• So, it was not possible to predict how many elements could be discovered between two elements especially when we considered the heavier elements.

Placing of heavier element before the lighter one:

• Few elements those possesses higher atomic mass were placed before elements having a lower atomic mass.

• Example - Argon(39.9) was placed before potassium(39.1), Cobalt(58.9) before Nickel(58.7), tellurium(127.60) before Iodine(126.9).