Modern periodic table

Modern periodic table

Modern periodic table is the latest version of periodic table which being followed worldwide. This periodic table is also called with other name like long for periodic table (or) extended periodic table (or) Bohr’s periodic table. Modern periodic table is based on Moseley’s periodic law. It was drafted by Niels Bohr. elements are arranged in various periods basing on “Aufbau” principle.
Some of the features of long form of periodic table are
1) It contains seven horizontal rows called periods and eighteen vertical columns called groups.
2) According to IUPAC system periods are numbered as one to seven and groups are numbered from one to eighteen periods.

First period

It is a shortest period. In this period elements 1s orbital is being filled with the electrons. It contains two gaseous elements, Hand He. This period is a discontinuous period

Second and third period

these two periods are called as short periods both of these periods the elements are having electrons only in ’s’ and ’p’ orbitals. Each period contains eight elements these two groups are discontinuous. The elements, which belong to second group are lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon. The elements that belong to third group elements are sodium, magnesium, aluminum, silicon, phosphorous, Sulphur, chlorine, argon.

Fourth and fifth period

Both of these periods are called as long periods and contain 18 elements each. In addition to ’s’ and ’p’ orbitals another orbital ’d’ is added. Due to the introduction of ’d’ orbital these groups became continuous groups. Fourth period starts with potassium and ends with krypton. Where as the fifth period starts with Rubidium and ends with xenon.

Sixth period

It is the longest period which contains 32 elements of which 14 elements belong to lanthanide series. In addition to ’s’,’p’, ’d’ another ’f’ orbital is added. The period starts with cesium and ends with Rn.

seventh period

It is an incomplete period, which contains incomplete period, which contains 23 elements including fourteen actinides which belong to ’f’ group. This group is still growing many new elements are still being excavated in some cases man made materials are also being used in this group.

Classification of elements in to blocks

Based on the entry of differentiating electron in to different orbitals. The elements are classified in to four blocks. They are
1) S-block
2) P-block
3) D-block
4) F-block


The elements in which the differentiating electron enters in to outermost ’s’ sublevel are called s-block elements. This block contains two groups Alkali metals (1A group elements) Alkaline metals (2A group elements). All the elements of s block are metals except Hydrogen. These act as good reducing agents and always ready to form ionic compounds.


The elements in which the differentiating electrons enter in to outer ’p’ sub level are called as P-block elements. It contains six groups starting from (3A to 7A) and zero group elements. This block contains all different types of metals, non-metals, metalloids, and noble gases.


The elements in which the differentiating electron enters in to (n-1)d sub shell are called d-block elements. It has ten groups they are 1Bto7B and eight. All the d-block elements are metals.


The elements in which the differentiating electron enters in to (n-2)f sub level are called F-block elements. F-block has two series of elements each series has fourteen elements. All the radioactive elements are actinides and most of them are synthetic.

Classification of elements based on properties

Elements are classified in to four types on the basis of their properties and electronic configuration. They are
1) Noble gases
2) Representative elements
3) Transition elements
4) Inner transition elements

Noble gases elements

They have completely filled valency shell with the electrons. The elements belonging to zeroth group in the periodic table are called noble gases. The elements belonging to this group are He, Ne, Kr, Xe, Rn. All the elements belonging to this group are very stable and inactive to any type of reactions. All the mono atomic gases except Rn all the remaining are present in the air.

Representative elements

This type is also called as main groups elements or normal elements. They have incompletely filled valency shell with the electrons. The elements of ’s’ and ’p’ block except zeroth group are called representative elements. In these elements last shell is incomplete. This type includes a few metals, all non metals and metalloids. These elements get nearest inert gas configuration by losing (or) gaining (or) sharing electrons, so they re chemically active.

Transition elements

They have incomplete filled two outer most shells. These are ’d’ block elements except 2B. in these elements last two shells of their atoms are incompletely filled. Due to small size of atom, high charge and unpaired electrons in ’d’ orbitals imparts characteristic properties to transition elements they are
a. These are hard and heavy metals
b. Have high melting and boiling points
c. These are good conductors of heat and electricity
d. Shows variable valencies
e. Exhibit color
f. These are generally paramagnetic
g. Forms alloys

Inner transition elements

These are F-block elements. They have incompletely filled three outer most shells. Lanthanides and actinides are included in this type. All these elements show common oxidation number +3 due to last two shells have similar configuration. The elements after uranium are called transuranic elements and synthetic elements. Lanthanides are known as rare earths.


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