How is the modern periodic table different from the table Mendeleev proposed?

Answer 1

The major difference is in the manner in which the elements are listed. Mendeleev used atomic weight. Today, we use atomic number.

Mendeleev used the atomic weight, which was known for many elements in his day (though not with the precision we know these values today), to put the known elements into some sort of order. The atomic number was unknown in Mendeleev's day (c. 1870). Henry Moseley would discover it in 1913.

The elements "traded places" in the periodic table a few times when Moseley demonstrated that the atomic number, or the number of protons in the nucleus, provided a more effective way to list the elements; for example, iodine and tellurium, as well as nickel and cobalt, were swapped.

A second distinction is that Mendeleev's proposed periodic table placed potassium after chlorine, for example, even though none of the noble gases were known in his day. Instead, they were discovered in the mid-1890s.

Of course, Mendeleev's greatest achievement was also to leave gaps in the table for several elements not yet identified by 1870, such as gallium and germanium; these gaps have since been filled in, and today all naturally occurring elements are known.

The table has been proposed in many different forms, beyond the well-known "long form" that is displayed on the walls of most high school chemistry classrooms. Mendeleev's original table would have seemed odd to a student of Chemistry today, but by 1871, the basic form that is used today was largely established.

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Answer 2

Mendeleev's table was not as precise in predicting the properties of yet-to-be-discovered elements, and the modern periodic table differs from it in a number of ways. First, it is arranged according to atomic number, whereas Mendeleev's table was arranged according to atomic mass. Secondly, the modern periodic table has more elements and is arranged into periods and groups, which reflects the electronic structure of atoms.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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