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bixtya [17]
3 years ago
8

Summarize the history of the periodic table

Chemistry
1 answer:
denis23 [38]3 years ago
6 0

Periodic table is the representation of elements in an order

The history of periodic table can be summarized as

a) 1829 :  Johann Dobereiner proposed the triad rule. According to him we can classify the elements in a triad where the atomic mass of middle element is average of atomic mass of the near by two atoms.

For example : Li, Na and K is a triad. Where atomic mass of Na is average of atomic mass of K

atomic mass of Na = 7+ 39 / 2 = 23

However, with the further discovery of elements the law was rejected.

b) 1864  : John Newland proposed the law of octave. According to him we can arrange the elements in a set of seven elements where the property of second set of seven elements will resemble the properties of first of seven elements or property will be repeated after seven elements. This was also rejected due to its limited applicability.

c)  Meyer : He arranged some 28 elements into six different families based on their atomic masses. The members of each familiy shared some common properties.

d) 1869 : Mendleev :  He actually developed a periodic table based on atomic mass of elements. He arranged the elements into groups and periods. He even left space for some undiscovered elements, which were later on discovered.

e) 1916 : Henry Moseley : He finally arranged elements based on their atomic number based on X-ray studies. He proposed the modern periodic law that the periodic properties of elements are due to atomic number of elements.



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Answer:

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Explanation:

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<u>Concentration of NaOH = 0.148 molar, M</u>

<u>Concentration of H3PO4 = 0.172 molar, M</u>

<u></u>

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This balanced equation tells us that neutralization of NaOH with HCl requires the same number of moles of each.  We just determined that the  moles of HCl used was 0.00370 moles.  Therefore, the 25.0 ml solution of NaOH had the same number of moles:  0.00370 moles NaOH.

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Now we need <u><em>three times</em></u> the moles of NaOH to neutralize 1 mole of H3PO4.

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     (0.00172 moles H3PO4)/(0.010 liters H3PO4)

<u>Concentration of H3PO4 = 0.172 molar, M</u>

 

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