What are the strengths and weaknesses of the Mendeleev periodic table?

Advantages:

1. Grouping of elements. He generalized the study of the elements then known to a study of mere 8 groups.

2. Gaps for undiscovered elements. Mendeleev left some gaps in his periodic table. These gaps were left for subsequent inclusion of elements not known at that time. He correctly thought that such elements would be discovered later.

3. Prediction of properties of undiscovered elements. He predicted the properties of then unknown elements om the basis of properties of elements lying adjacent to the vacant slots.

4. Incorrect masses corrected. He was able to correct the values of atomic mass of elements like gold and platinum by placing these elements strictly on the bases of similarities in their properties.

Disadvantages:

1. Anomalous pairs: Argon with atomic mass 39.9 precedes potassium with atomic mass 39.1.

Cobalt with atomic mass 58.9 precedes nickel with atomic mass 58.6.

Tellurium with atomic mass 127.6 precedes iodine with atomic mass 126.9.

2. Position of isotopes: According to Mendeleev's periodic law, isotopes of an element must be given separate places in the periodic table since they have different atomic masses. But they were not assigned separate places.

3.Grouping of chemically dissimilar elements: Elements such as copper and silver bear no resemblance to alkali metals but they have placed in separate groups.

4.Separation of chemically similar elements: Elements that are chemically similar, such as gold and platinum have been placed in separate groups.

5.Electron arrangement: It does not explain the electron arrangement of elements.

6. Position of Hydrogen: It was not given in a fixed position.Explanation:

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

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