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

Newland's law of octaves

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

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

I found 2 different versions of Mendeleev's table , first in which sodium is placed with copper and all. Second sodium is placed with potassium  , lithium etc(like modern table's group 1 elements) which kinda make sense.

First,

Second,

But mostly i found the first category table on internet.

I am confused with positioning , as example sodium is put with copper, silver, gold, although they have very different properties even today's modern periodic table has 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?

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

Newland's law of octaves

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,

Second,

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?

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

Newland's law of octaves

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

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

I found 2 different versions of Mendeleev's table , first in which sodium is placed with copper and all. Second sodium is placed with potassium , lithium etc(like modern table's group 1 elements) which kinda make sense.

First,

Second,

But mostly i found the first category table on internet.

I am confused with sodium positioning and also why elements are arranged in zig zag order in group in first table not in a single straight line?

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

Newland's law of octaves

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

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

I found 2 different versions of Mendeleev's table , first in which sodium is placed with copper and all. Second sodium is placed with potassium , lithium etc(like modern table's group 1 elements) which kinda make sense.

First,

Second,

But mostly i found the first category table on internet.

I am confused with positioning , as example sodium is put with copper, silver, gold, although they have very different properties even today's modern periodic table has 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?