I understand that John Newland’s law of octaves was ridiculed by the scientific community as his table failed to work past calcium. I'm trying to understand how Mendeleev’s table improved on this.

On Mendeleev’s table, do all elements in the same group even past calcium exhibit similar properties? I saw on his table that potassium and copper were in the same group. Calcium and zinc were also in the same group. It seems to me that these elements have different properties.

So why was this accepted? Don't potassium and copper exhibit different properties as well as calcium and zinc? To me, it appears that both Newlands and Mendeleev's tables had elements in the same group with very different properties.


2 Answers 2


Neither Mendeleev or Newland could properly account for the transition metals in their tables.
Newland used atomic mass as the foundation of his table, while Mendeleev (and Meyer) used other properties, such as density in addition to atomic mass. What set Mendeleev apart is that he did not assume that all of the elements had been discovered. Consequently, he left blank spaces on his table at atomic masses 44, 68, 72, and 100. These spaces correspond to the elements scandium, gallium, germanium and technetium.

It's true that we credit Mendeleev with creating the modern periodic table, but his table was ordered by atomic mass, while the current table is ordered by atomic number. This is based on work by Moseley around 1913.


All those groups of two elements are situated in columns, where the number of the column gives at least one of the oxidation numbers of the included elements. Let us look at all elements in the fourth line, from Potassium (19) to Bromine (35)

$1$) In $1$st column, Potassium(19) and Copper(29) have in common the possibility of being stable at oxidation number $+1$.

$2$) In $2$nd column, Calcium(20) and Zinc(30) have the same oxidation number $+2$.

$3$) In $3$rd column, Scandium(21) and Gallium(31) have the same oxidation number $+3$.

$4$) In $4$th column, Titanium(22) and Germanium(32) have the oxidation number $+4$.

$5$) In $5$th column, Vanadium(23) and Arsenic(33) can have the oxidation number $+5$.

$6$) In $6$th column, Chromium(24) and Selenium(34) can both have the oxidation number $+6$,

$7$) In $7$th column, Manganese(25) and Bromine(35) can both have the oxidation number $+7$.

The only trouble is the "triplet" of the $8$th column : Iron(26) - Nickel(27) - Cobalt(28), which have oxidation number +$2$ and sometimes +$3$ !! Nobody was able to explain this strange behavior and the absence of corresponding atoms after Bromine at the end of the $19$th century. Mendeleev was hoping that this strange behavior would be explained later on, in the future. A couple of years later on, the noble gas were discovered and were also put in this mysterious $8$th column.


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