(i) Elements with large difference in properties were included in the same group.
Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).
(ii) No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).
(iii) The increasing order of atomic mass was not strictly followed throughout.
Eg: Co & Ni, Te & I.
(iv) No place for isotopes in the periodic table.

In modern periodic table the horizontal rows are called periods. There are seven periods in the periodic table. Vertical columns starting from top to bottom are called groups. There are Eighteen groups in the periodic table.

(i) The table is based on a more fundamental property i.e., atomic number.
(ii) It correlates the position of the element with its electronic configuration more clearly.
(iii) The completion of each period is more logical. In a period, as the atomic number increases, the energy shells are gradually filled up until an inert gas configuration is reached.
(iv) It is easy to remember and reproduce.
(v) Each group is an independent group and the idea of subgroups has been discarded.
(vi) One position for all isotopes of an element is justified, since the isotopes have the same atomic number.
(vii) The position of the eighth group (in Mendeleev's table) is also justified in this table. All transition elements have been brought in the middle as the properties of transition elements are intermediate between left portion and right portion elements of the periodic table.
(viii) The table completely separates metals from nonmetals. The nonmetals are present in upper right corners of the periodic table.
(ix) The positions of certain elements which were earlier misfit (interchanged) in the Mendeleev's periodic table are now justified because it is based on atomic number of the elements.
(x) Justification has been offered for placing lanthanides and actinides at the bottom of the periodic table.

(i) Alloys do not get corroded or get corroded to very less extent.
(ii) They are harder and stronger than pure metals (Example: Gold is mixed with copper and it is harder than pure gold)
(iii) They have less conductance than pure metals (Example: Copper is good conductor of heat and electricity whereas brass and bronze are not good conductors)
(iv) Some alloys have lower melting point than pure metals (Example: Solder is an alloy of lead and tin which has lower melting point than each of the metals)
(v) When metal is alloyed with mercury, it is called amalgam.

Features of modern periodic table:
(i) All the elements are arranged in the increasing order of their atomic number.
(ii) The horizontal rows are called periods. There are seven periods in the periodic table.
(iii) The elements are placed in periods based on the number of shells in their atoms.
(iv) Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
(v) Based on the physical and chemical properties of elements, they are grouped into various families.

The elements of group 3 to 12 have their valence electrons in their outermost d subshells. These elements are called d block elements.

d-block elements are found in the centre of the periodic table. Their properties are intermediate to that of s-block and p-block elements and so they are called transition elements.

a) Dobereiner
b) Newlands
c) Mendeleev

Elements which have the properties of both metals and non-metals are called as metalloids. (eg) Boron, Arsenic.

Alloys are mixtures of two or more metals and are formed by mixing molten metals thoroughly. Rarely nonmetals are also mixed with metals to produce alloys.