Mendeleev created his Periodic Table at the time when presence of sub-atomic particles like electrons, protons and neutrons were not discovered.So, the term atomic number was not known till now.
So , he positioned the elements in increasing order of atomic mass because Atomic Mass of many elements discovered till then were known.
He wanted them to be in a pattern , that repeated every seven elements. His Table became known as the Periodic Table . He arranged the elements in order of increasing atomic mass.
Their physical properties and chemical reactivity.
The properties he used were density,appearance,and melting point
atomic mass
to classify the elements mendeleev arranged the elements in increasing order of their atomic mass
Elements with same property are grouped together. Property can be estimated by its position.
Oxygen is placed in the second period of the Mendeleev table.
Examples: density, melting point, atomic weight, density and formula of oxide.
What elements are similar to iron in a chemical property on the Periodic Table
Atomic Mass.
to classify the elements mendeleev arranged the elements in increasing order of their atomic mass
Known elements were arranged by increasing mass.
Mendeleev created his Periodic Table at the time when presence of sub-atomic particles like electrons, protons and neutrons were not discovered.So, the term atomic number was not known till now. So , he positioned the elements in increasing order of atomic mass because Atomic Mass of many elements discovered till then were known.
Elements with same property are grouped together. Property can be estimated by its position.
Mendeleev predicted that gallium will be a metal.
the number of protons in the nucleus and the number of electrons in the valence orbital
Madeleev originally arranged the elements in the first periodic table by their average atomic masses. Later it was changed to atomic number by Moseley, or the number of protons each of that element's atom has.
atomic no. or basically according to the no. of electrons in their outermost shell whcih reflect the property of individual atom
atomic mass
The basic organization structure was by atomic mass, which while it may follow a trend of increasing with each progressing element on the modern table, which is organized by atomic number or number of protons, there are a few exceptions, such as Argon having a greater atomic mass than Potassium, even though Argon has one less proton.
Oxygen is placed in the second period of the Mendeleev table.