- It is tabular arrangement of elements in groups or periods
- Periodic table provides basic framework to study the periodic behavior of physical and chemical properties of elements as well as their compounds
- It organizes elements according to trends so that you can see the relationships between them.
His contributions were based on the physical and the chemical properties
A German chemist, arranged known elements in groups called Triads.
Elements can be classified in triads where the atomic weight of middle element of each triad is almost equal to the arithmetic mean of atomic weights of other elements
An English chemist, he gave Law of octaves , if elements are arranged in order of their increasing atomic weights, every 8th element starting from a given one has similar properties as that of first one
A Russian chemist, Dmitri Mendeleev, he said that physical and chemical properties of elements are periodic functions of their atomic weights
Mosley said that the physical and chemical properties of elements are periodic functions of their atomic numbers.
- The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.
- Elements which are similar regarding their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g. K, Rb, Cs).
- The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
- The elements which are the most widely diffused have small atomic weights.
- The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
- We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.
- The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring.
Certain characteristic properties of elements can be foretold from their atomic weights.
- Arrangement of elements in ascending order of atomic numbers to rectify four misfit pair of elements in the Mendeleev’s Periodi Table i.e. K & Ar, Ni & Co, I & Te.
- Addition of group VIII to properly place the newly discovered noble gases.
- Introduction of two types of vertical groups A and B to eradicate the misplacement of Zn Cd & Hg and Be, Mg, Ca, Sr & Ba in same vertical group and so many others in same manner.
- No concepts of isotopes and position of isotopes
- No position of Hydrogen
- No concept of atomic number
- No concepts of electronic configuration
- No concepts of normal and transition elements
- No concepts of lanthanides and actinides
- No concept of atomic size or volume
- A Subgroups:
The subgroups containing the representative or normal elements are labelled as A subgroups
- B Subgroups:
B subgroups contains less typical elements, called Transition elements and are arranged in the center of the periodic table.
K — 1s2, 2s2, 2p6, 3s2, 3p6, 4s1