(i) Number of electrons in outermost shell: The number of electrons present in the outermost shells does not change on moving down in a group, i.e remains the same. Hence, the valency also remains same within a group.
(ii) Number of shells: In going down a group the number of shells increases by one at each step and ultimately becomes equal to the period number to which the element belongs.
(iii) Valency: The valencies of all the elements of the same group are the same. The valency of an element with respect to oxygen is same in a group.
(iv) Metallic character: The metallic character of the elements increases in moving from top to bottom in a group.

(i) Number of electrons in outermost shell: The number of electrons present in the outermost shell increases from 1 to 8 as we proceed in a period.
(ii) Number of shells: As we move from left to right in a period the shells remains the same. The number of shells present in the elements corresponds to the period number. For example all the elements of 2^nd period have on 2 shells (K, L)
(iii) Valency: The valency of the elements increases from left to right in a period. With respect to hydrogen, the valency of period elements increases from 1 to 4 and then falls to one. With respect to oxygen, the valency increases from 1 to 7.
(iv) Metallic character: The metallic character of the elements decreases across a period.
For example: 3rd period  

Merits of Moseley's long form of periodic table:
(i) As this classification is based on atomic number, it relates the position of an element to its electronic configuration.
(ii) The elements having similar electronic configuration fall in a group. They also have similar physical and chemical properties.
(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) The position of zero group is also justified in the table as group 18.
(v) The table completely separates metals and non-metals.
(vi} The table separates two subgroups, lanthanides and actinides, dissimilar elements do not fall together.
(vii) The greatest advantage of this periodic table is that this can be divided into four blocks namely s, p, d and f-block elements.
(viii) This arrangement of elements is easier to remember, understand and reproduce.

(i) The long form of periodic table of the elements is constructed on the basis of modem periodic law. The arrangement resulted in repeating electronic configurations of atoms at regular intervals.
(ii) The elements placed in horizontal rows are called periods and in vertical columns are called groups.
(iii) According to IUPAC, the groups are numbered from 1 to 18.
(iv) There are 18 vertical columns which constitute 18 groups or families. All the members of a particular group have similar outer shell electronic configuration.
(v) There are 7 horizontal rows called periods.

The elements are shown in the above table along with its atomic number.
(vi) The atomic number also indicates the number of electrons in the atoms of an element.
(vii) This periodic table is important and useful because we can predict the properties of any element using periodic trend, even though that element may be unfamiliar to us.

Anomalies of Mendeleev's periodic table
(i) Some elements with similar properties were placed in different groups whereas some elements having dissimilar properties were placed in same group, but iodine (127) was placed in VII group.
Example: Tellurium (127.6) was placed in VI group.
(ii) Some elements with higher atomic weights were placed before lower atomic masses in order to maintain the similar chemical nature of elements. This concept was called inverted pair of elements concept.
Example: ⁵⁹₂₇Co and ^58.7 ₂₈Ni
(iii) Isotopes did not find any place in Mendeleev's periodic table.
(iv) Position of hydrogen could not be made clear.
(v) He did not leave any space for lanthanides and actinides which were discovered later on.
(vi) Elements with different nature were placed in one group, Example: Alkali metals and coinage metals were placed together:
(vii) Diagonal and horizontal relationships were not explained.