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I have been recently studying periodic classification. I am having some confusion regarding old periodic classification.

Newland's law of octaves

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In that you can see, in the 4th horizontal line, cobalt and nickel in one slot. When I ask the reason, many web sites and books describe it as "in order to fit elements, he keeps many elements under one slot."

But I thought, "Why he didn't place nickel next to cobalt in another slot? Can't he?"

Why under one slot necessary although he knew they are unlike elements?

In Mendeleev's periodic table, if you look, he places 'Na' sodium in the same group with copper and silver, while they are totally different. Sodium is very reactive, unlike copper, silver, and gold.

I found 2 different versions of Mendeleev's table: the first in which sodium is placed with copper and all, and the second in which sodium is placed with potassium, lithium etc. (like modern table's group 1 elements) -- that kind of makes sense.

First,

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Second,

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But mostly I found the first category table on the internet.

I am confused with positioning; for example, sodium is put with copper, silver, and gold, although they have very different properties -- even today's modern periodic table has a different group for them.

And also why elements are arranged in zig zag order in group in first table not in a single straight line?

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But I thought " why he didn't place nickel next to cobalt in another slot? Can't he?"

Newland ordered his table by atomic mass. "According to the law of octaves, every eighth element in the above table must share similar physical and chemical properties." This pattern starts to break down after calcium. Newland thought thay cobalt and nickle, platinum and iridium, cerium and lanthanum each pair had the same atomic weight.

I am confused with positioning; for example, sodium is put with copper, silver, and gold, although they have very different properties -- even today's modern periodic table has a different group for them.

You are looking at what is called a short form periodic table. Apparently they are popular in former USSR countries. It shows how atoms have similar highest oxidation states, and chemical similarities based on the valence shell.

And also why elements are arranged in zig zag order in group in first table not in a single straight line?

If you look at the top of the table you see "A B" in each group. The elements under them are arranged left to right according to group. Then you can see Sodium isn't put together with gold, copper, and silver. It goes group IA: H, Li, Na, K, Rb, CS and in group IB: Cu, Ag, Au. In this scheme Group IA is equivalent to group 1 in the IUPAC table and group IB is equivalent to group 11.

Below is a modern version of the short form periodic table that has a much better layout. x

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    $\begingroup$ "It shows how atoms have similar highest oxidation states, and chemical similarities based on the valence shell." Do u mean mendeleev Arrange in each column based on valenve shell electron?As all in group 1 of mendeleev table i attached has same valence electron no? But not similar properties though! Like Cu and Na?doesnt he knew Cu and Na have compketely different properties of reaction? $\endgroup$ Mar 13, 2022 at 9:09
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    $\begingroup$ True, I should have stated the pattern starts to break down at potassium. It is handy to see that copper and potassium have 1 valance electron. Due to copper's d orbital reactively it's similar to both Alkali or alkali earth metals. Copper (Cu2O) can form oxides like potassium (K2O). If copper (CuF2) reacts with halogens it can act more like calcium(CaF2). It all depends on the Oxidation state of copper. Cu(I) can form CuF and Cu2O. Cu(II) can form CuF2 and CuO. That said when copper and potassium have the same number of electrons as protons they both have 1 electron in the 4s orbital. $\endgroup$
    – SBoZon
    Apr 7, 2022 at 20:39
  • $\begingroup$ But at that time when he arranged them, then he didn't knew abt atomic no. He just arrange them by writting each element chemical reaction eg. R2O , RO etc...on paper. Then won't he found that Cu can react with O2 and exust in both form as R2O as well as RO! Then also why he put Cu in R2O grp only!? Won't he be confused btw R2O and RO grp for Cu?? As he didnt know abt atm. No. Also at that time i.e valence electron similarity? Than also he is so sure to put it in R2O grp not in RO! $\endgroup$ Apr 9, 2022 at 10:55
  • $\begingroup$ He kind of did this is a Mendeleev table from 1870. You can see he puts Cu in small print in Group 1 and Group 8. By 1900 the table had put Cu in group 1. $\endgroup$
    – SBoZon
    Apr 26, 2022 at 16:39
  • $\begingroup$ Apparently the European long form table doesn't group the elements 1-18 they still use the short form Group 1-8 A or B. $\endgroup$
    – SBoZon
    Apr 26, 2022 at 16:40

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