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" The properties of the elements are a periodic function of their atomic weights " . Prove this statement.. With the conclusions given by Mendeleev!!
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According to Kaji (2003), as early as 1864, in a lecture on theoretical chemistry Mendeleev stated: “In fact, while the atomic theory was strongly supported by the law of definite chemical compounds, it was also challenged by the so-called indefinite compounds” (p. 194). This shows Mendeleev’s ambivalence (which we stressed throughout our article) and also the acknowledgment of the relationship between the atomic theory and the law of definite proportions. Interestingly, these views were expressed by Mendeleev a full 25 years before the Faraday Lecture;
In response to our Step 5 (Niaz et al., 2004, pp. 274-275), Scerri stated: “Contrary to what the authors conclude in the final line quoted above, this statement is not an acknowledgment of any role played by atomic theory. Mendeleev consistently argued against the unity of matter and against Prout’s hypothesis to that effect” (p. 8). If we read once again Mendeleev’s quote in Step 5, it will reveal that it was not the question of Prout’s hypothesis (which Mendeleev denied and we noted in our article, p. 275), but rather Dalton’s law of multiple proportions, which was at stake. Actually, Mendeleev (1889) himself explains the data presented with respect to the oxides in Step 5, in the following categorical terms: “The periodic law has clearly shown that the masses of the atoms increase abruptly, by steps, which are clearly connected in some way with Dalton’s law of multiple proportions.” (p. 642). It is interesting to note that we cited this explanation by Mendeleev in Niaz et al (2004, p. 275) and for some reason Scerri decided to ignore it! Similarly, Weisberg (2007) has endorsed a similar thesis: “Mendeleev showed that the quantity of oxygen in the oxides was a periodic function of the element’s group (column) on the Periodic Table. This can be accounted for by the Periodic Law, but would have remained mysterious otherwise” (pp. 214-215). Furthermore, Dalton’s law of multiple proportions is considered as evidence to corroborate the atomic theory by the dean of modern chemistry: “The discovery of the law of multiple proportions was the first great success of Dalton’s atomic theory. This law was not induced from experimental results, but was derived from the theory, and then tested by experiments” (Pauling, 1964, p. 26). The similarity between the explanation provided by Mendeleev in 1864, 1889 and its endorsement by Pauling in 1964 is striking indeed!
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→ IT is based on the principle that , if atoms are arranged in the increasing order of their weight , after a regular interval , the periodic properties are repeated .
e.g
" physical and chemical properties of atoms are periodic function of their atomic weight ."
→ It contains 8 vertical ( group) and 12 horizontal ( period ) rows . Zero group elements were not known during that time . it is made of 63 elements .
★ As we know that periodic table was first of all ,proposed by Mendenleef on the basis of atomic weight .After it's it was modified three times .the very first modification done by Mendeleef itself and he proposed the table with 9 GROUPS ( named from zero to VIII ) and 12 PERIODS ( named from 1 to 12).
Mendeleev's periodic table:
1)It is based on atomic weights.
2)Mendeleev's periodic law:The physical and chemical properties are periodic function of their atomic weights
.
3)Only 63 elements were known at that time.
4)It has 8 vertical columns called groups .
5)7 horizontal rows known as periods.
6)Order of atomic weights was changed at places to justify properties of an element.
7)It had vacant places which were discovered later.
Example: eka aluminium (gallium), eka silicon ( germanium)