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1)The elements in the periodic table are arranged in the increasing order of their atomic number or electronic configurations
2) The horizontal rows are called as "periods".
3) The vertical columns are called as " groups"
4)The Modern periodic table consists of 7 periods and 18 groups.

PERIODS :- a) Each period starts with an alkali metal and ends with an inert gas element.  b) Elements present in the same period have same number of shells which is equal to the periodic number.   c) The 1st period is the shortest period containing only 2 elements i.e. Hydrogen (H) & Helium (He). In this period, only the 1s orbital is filled.   d) The 2nd period contains 8 elements starting with Lithium (Li) and ending with Neon (Ne). In this period, the 2s & 2p orbitals are filled.   e) The 3rd period also contain 8 elements starting with Sodium (Na) and ending with Argon (Ar). In this period the 3s & 3p orbitals are filled.   f) The 4th period is the long period with 18 elements, starting with Potassium (K) and ending with Krypton (Kr). In this period, 4s & 4p and also the 3d orbitals are filled.   g) The 5th period is also the long period with 18 elements, starting with Rubidium (Rb) and ending with Xenon (Xe). The 5s & 5p along with 4d orbitals are filled.   h) The 6th period is the longest period with 32 elements. It not only includes 10 elements belonging to 5d series i.e. from Lanthanum (La) to Mercury (Hg) but also contains 14 elements belonging the 4f series called lanthanides i.e from Cerium (Ce) to Lutetium (Lu). In this period, the 6s & 6p along with the 4f & 5d orbitals are filled.   i) The 7th period is an incomplete period. It includes Fr along with the 14 elements belonging to 5f series called actinides i.e from Thorium (Th) to Lawrencium (Lr). In this period, the 7s & 5f orbitals are filled.   GROUPS :- a) The Modern Periodic Table consists of 18 groups or vertical columns.   b) Elements present in the same group show same physical and chemical properties.   c) Also the elements present in the same group have same number of electrons in the outermost shell.   d) According to American convention, the groups are denoted by roman numerals followed by either an capital alphabet "A" if the group is in the s-block or p-block, or by "B" if the group is in the d-block .   e) Thus the groups from 1 to 18 are denoted as IA , IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB ,IIB, IIIA, IVA, VA, VIA, VIIA and 0 (zero).   f) The elements from IA to VII A group i.e the elements in the groups 1, 2, 13, 14, 15, 16 & 17 are called as representative elements.   g) The 18th group or zero group elements are called as inert gases or noble gases . This group includes the elements He, Ne, Ar, Kr, Xe and Rn.   h) The elements in the groups from IIIB to IIB i.e., from group 3 to 12 are called as transition elements .   i) The two rows placed at the bottom of the periodic table i.e the Lanthanides and Actinides are also considered to be the part of IIIB group (i.e. group 3). These are usually called as inner transition elements .   The 14 elements with atomic number 58 to 71 are called as Lanthanides, whereas the 14 elements with atomic number 90 to 103 are called as Actinides.   Classification of Elements :- At present elements upto atomic number 118 are known of which the recently discovered elements are man-made. With such a large number of elements,it is very difficult to study the chemistry of the individual elements and the innumerable compounds they form.Hence it is necessary to classify the elements for their systematic and organised studies. Therefore the Elements in the Periodic Table are classified on the basis of their electronic configuration into 4 blocks as s , p , d and f .    1. S-block :- The Group 1 and 2 elements contain 1 or 2 electrons in their outermost shell and are called as s-block elements.   2. P-block :-The elements in the Groups from 13 to 17 and the 0 (zero ) group elements contain 3 to 8 electrons in their outermost shell and are called as p-block elements.   3. D-block :- The elements in the Groups from 3 to 12 contain 1 to 2 electrons in their outermost shell and are called as Transition elements. They are all metals.   4. F-block :- The 14 elements with atomic number 58 to 71 are called as Lanthanides whereas the 14 elements with atomic number 90 to 103 are called as Actinides.These 28 elements are collectively called as f-block elements.

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The features of the Periodic Table are :-
The elements that have like physical and chemical properties are found in vertical columns;The vertical columns are called groups;The vertical columns are numbered from 1 to 8;Each number is followed by a letter: A or BA groups contain main elements and B groups contain transition elementsThe name of the horizontal row is period;The period that contains only H and He has the number 1.The properties of the elements divide the the periodic table in areas that are marked with different colors;The elements of the periodic table belong to 3 groups: metals, nonmetals, metalloids;Metalloids are located to the boundary between metals and nonmetals;The elements located to the left end of the period, have a metallic character;The properties of the elements from B (boron) to Te (tellurium) make difficult their classification (metals or nonmetals). 
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