Moseley's Periodic Table - Home of Knowledge

Moseley’s Periodic Table




In 1913 Henry Moseley discovered a new property of elements, the atomic number. He states that atomic number determines the position of elements. He arranged elements based on their increasing atomic number in periodic table.


Modern periodic law; – “properties of elements are periodic functions of their atomic number”.

According to Moseley atomic number is basic property of an element due to two aspects;

  • Atomic number increases regularly from element to element.
  • It is fixed for each and every element.


 Salient features of long form of periodic table;

1) This table consists of seven horizontal rows called periods.

  • First period consists of only two elements and is called short period.
  • Second and third period consists of 8 elements each and are called normal periods.
  • Fourth and fifth period consists of 18 elements each and are called long periods.
  • Sixth period has 32 elements and is called very long or longest period.
  • Seventh period has 23 elements and is incomplete. This is also called very long period.
  • Elements of a period show different properties.
  • Elements of a period show same number of shells.
  • There are 18 vertical columns in the periodic table called groups.
  • These groups are numbered 1 to 18 from left to right.
  • Elements of a group show same chemical properties due to same electronic configuration.
  • Elements are classified into four blocks depending upon the type of sub-shell that receives last electrons.


Periods in Modern PERIODIC table; – The horizontal rows in periodic table are called periods. Atomic number in a period continuously increases. There are seven periods in modern periodic table.

  • First period or short period:- first period is called short period. This period consists of only two elements named Hydrogen(H) and Helium(He).
  • Second period or normal period:-it consists of 8 elements, named Lithium(Li), Beryllium(Be), Boron(B) , Carbon(C), Nitrogen(N) ,Oxygen (O), Fluorine(F), and Neon (N).
  • Third period: – this period is also called Normal period. It consists of 8 elements , sodium (Na) , Magnesium(M), Aluminum(Al) , Silicon(Si) , Phosphorous(P) , Sculpture or sulfur(S), Chlorine (Cl) and Argon (Ar).
  • Longs periods; –Fourth and fifth periods are called long periods, each consists of 18 elements.
  • Very long periods;-6th and 7th periods are called very long periods. 6th period contain 32 elements, while seventh period contain 23 elements and is incomplete period.
  • Lanthanides; – the series that starts after Lanthanum is called Lanthanide series. It contains 14 elements and is present in f block.
  • Actinides; – The series that starts after Actinium is called actinide series. It contains 14 elements and is present in f blocks.


Groups in modern periodic table;- There are 18 vertical columns in the periodic table called groups.

These groups are numbered 1 to 18 from left to right.

Elements of a group show same chemical properties due to same electronic configuration due to presence of same number of valence electrons.

GROUP 1 or Alkali metals;- it consists of hydrogen, lithium, sodium, potassium, rubidium, cesium and francium. All have 1 electron in outermost shell and thus all have general electronic configuration nS1..

Group 2 or Alkaline earth metals:- Group 2 consists of Beryllium, Magnesium, Calcium, Strontium, Barium and Radium. All OF them have 2 electrons in their valence shells having electronic configuration ns2.

Group 3 to 12 (Transition metals) :- This group is also called d-block elements. In these elements last electrons enters into d-sub-shell, so named d block elements.

Group 13 or Boron family: The boron family contains the semi-metal boron (B) and metals aluminum (Al), gallium (Ga),indium (In), and thallium (Tl). All of them have 3 electrons in valence shell and have general electronic configuration ns2, np1.


Group 14 Elements or Carbon family:- The carbon family, Group 14 in the p-block, contains carbon (C), silicon (Si), germanium(Ge), tin (Sn), lead (Pb), and flerovium (Fl). Each of these has 4 electrons in last shell. Each of these elements has only two electrons in its outermost p orbital: each has the electron configuration ns2np2.


 Group 15 Elements The nitrogen family:- includes the following compounds: nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). All of them have 5 electrons in outermost shells and so have general electronic configuration ns2np3. .


GROUP 16 The oxygen family,:-  also called the chalcogens, consists of the elements found in Group 16 of the periodic table and is considered among the main group elements. It consists of the elements oxygensulfur, seleniumtellurium and polonium. They have 6 electrons in outermost shell and have general electronic configuration ns2 ,np4


  Group 17 or halogen family:-  The Halogens are, Fluorine, Chlorine, Bromine, Iodine and Astatine. All of them have 7 electrons in outer most shell having general electronic configuration ns2, np5


All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable. Helium, Neon, Argon, Krypton, Xenon and Radon. They all have general electronic configuration of ns2, np6..


Hydrogen (H) and helium (He) are special elements. Hydrogen can have the electron traits of two groups: one and seven. For chemists, hydrogen is sometimes missing an electron like the members of group IA, and sometimes has an extra one as in group VIIA. When you study acids and bases you will regularly work with hydrogen cations (H+). A hydride is a hydrogen anion and has an extra electron (H-).

Helium (He) is different from all of the other elements. It is very stable with only two electrons in its outer orbital (valence shell). Even though it only has two, it is still grouped with the noble gases that have eight electrons in their outermost orbitals. The noble gases and helium are all “happy,” because their valence shell is full.


Blocks of modern periodic table:- Modern periodic table is divided into four blocks depending on type of sub shell in which the last electron present. Based on completion of sub shells, elements with similar sub shell electronic configuration are referred as a block of elements. There are four blocks in modern periodic table.


  • S Block Elements; –those elements in which last electrons is present in S sub shell are included in s block. Group 1 and 2 elements are present in this block.
  • P Block Elements:-those elements in which last electrons present in p sub shell are called p block elements. This block contains group 13 to 18 elements, except Helium.
  • d Block elements:-this group include all those elements that have last electrons in their outermost shell. Group 3 to 12 elements are present in this block.
  • f Block elements:- the elements in which last electron present in f sub shell are called f block elements. This block includes Lanthanide and Actinide series ad is present at the bottom of periodic table.

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