d] Give reasons why Mendeleeff's Periodic Table was not completely accepted
the Modern Periodic Table.
Answers
Answer:
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Explanation:
In devising his table, Mendeleev did not conform completely to the order of atomic mass. He swapped some elements around. ... He corrected the known atomic masses of some elements and he used the patterns in his table to predict the properties of the elements he thought must exist but had yet to be discovered.
Answer:
atomic mass increases from top to bottom of vertical columns, with successive columns going left to right. As a result, elements that are in the same horizontal row are groups of elements that were known to exhibit similar chemical properties. One of Mendeleev’s insights is illustrated by the elements tellurium (Te) and iodine (I). Notice that tellurium is listed before iodine even though its atomic mass is higher. Mendeleev reversed the order because he knew that the properties of iodine were much more similar to those of fluorine (F), chlorine (Cl), and bromine (Br) than they were to oxygen (O), sulfur (S), and selenium (Se). He simply assumed that there was an error in the determination of one or both of the atomic masses. As we will see shortly, this turned out not to be the case, but Mendeleev was indeed correct to group these two elements as he did.
Notice that there are several places in the table that have no chemical symbol, but are instead labeled with a question mark. Between zinc (Zn) and arsenic (As) are two such missing elements. Mendeleev believed that elements with atomic masses of 68 and 70 would eventually be discovered and that they would fit chemically into each of those spaces. Listed in the Table 1 are other properties that Mendeleev predicted for the first of these two missing elements, which he called “eka-aluminum,” compared with the element gallium.
Table 1
Eka-Aluminum (Ea) Gallium (Ga)
Atomic mass 68 amu 69.9 amu
Melting point Low 30.15°C
Density 5.9 g/cm 3 5.94 g/cm 3
Formula of oxide Ea 2 O 3 Ga 2 O 3
The element gallium was discovered four years after the publication of Mendeleev’s table, and its properties matched up remarkably well with eka-aluminum, fitting into the table exactly where he had predicted. This was also the case with the element that followed gallium, which was named eventually named germanium.
Mendeleev’s periodic table gained wide acceptance with the scientific community and earned him credit as the discoverer of the periodic law. Element number 101, synthesized in 1955, is named mendelevium after the founder of the periodic table. It would, however, be several years after Mendeleev died before the several discrepancies with the atomic masses could be explained and before the reasons behind the repetition of chemical properties could be fully explained