Saturday, 7 December 2019

Modern Periodic Table

  Admin       Saturday, 7 December 2019
Modern Periodic Table - In the year 1913, an English physicist, Henry Moseley, a young physicist from England, studied the frequencies of the X-rays which were emitted when certain metals were bombarded with high-speed electrons. He found that in all the cases, the square root of the frequency (v) was directly proportional to the atomic number of the atom of the metal.

These studies led Moseley to believe that instead of atomic mass, atomic number is the fundamental property of an element. In the light of the above observations, Moseley gave the modern periodic law which states that



Modern Periodic Table


Modern Periodic Table

The physical and chemical properties of the elements are the periodic function of their atomic number.



The elements with a different electronic arrangement of the atoms possess different chemical properties. As the number of electrons in an atom is given by the atomic number and not by the mass number, therefore, the atomic number should form the basis of the classification of the elements in the Modern Periodic Table and not the atomic mass as predicted by Mendeleev.




Need for Modern Periodic Table



Need for Modern Periodic Table - A shopkeeper dealing in different items say stationary, cosmetics, confectionery, etc. place things of one type in one place. In the library, books on one subject are placed in one almirah. This is done for convenience and to make things easy and simple.

Similarly, a total of 118 natural and synthetic elements are known. These elements have different physical and chemical properties and they combine with one another to form millions of compounds each having different properties. It becomes difficult to study the properties of elements and their compounds individually because of their vast numbers. So there is a need for a modern long-form of table.


Why Change in Chemical and Physical Properties?

Each atom or molecule has a center called a nucleus. It contains two major particles a proton and a neutron. Protons are positively charged and neutrons are electrically neutral. Electrons whirling around the nucleus are negatively charged particles. These electrons move in paths that are arranged in energy levels. The outermost energy level is most stable when it contains eight electrons. 

  • The chemical and physical properties of elements depend on the outermost electron present. Noble gases like neon, argon and other noble gases have its full number eight electrons in its outermost energy level. This causes all the noble gases to remain inert and chemically stable.

ElementElectronic Config.Shells 
 He 1s2 2
Ne[He] 2s2sp62,8
Ar[Ne] 3s23p62,8,8
Kr[Ar] 3d104s24p62,8,18,8
Xe[Kr] 4d105s25p62,8,18,18,8
Rn[Xe] 4f145d106s26p62,8,18,32,18,8

  • Whether an element combined to form a compound or not depends on the arrangement of electrons in the outermost energy level. If this outermost energy level is completely filled with electrons, the element is chemically stable and will not bond.


Henry Moseley put forward the modern periodic law, which states that the properties of elements are the periodic functions of their atomic number. That is, if the elements are arranged in tabular form in the increasing order of their atomic numbers, then the properties of the elements and valence electrons are repeated after definite regular intervals or periods.

Groups and Period Modern Periodic Table


The periodic table Groups and periods help us to predict the chemical properties of elements having similar behavior. So, the modern periodic table has many important features. In a periodic table, all the elements have been arranged in the increasing order of their atomic numbers. It means the arrangements are based upon modern periodic law. This arrangement consists of
  • 18 vertical columns called groups or families.
  • 7 horizontal rows called periods or series.
  • Four blocks namely s, p, d and f blocks.

Modern Periodic Table groups periodic

Periodic Table Groups Names

A vertical column from top to bottom in the periodic table is known as a group.
According to the latest recommendation of the International Union of Pure and Applied Chemistry (IUPAC), the periodic table groups are numbered from 1 to 18. All the members of a particular group have similar outer shell configuration.
  1. The elements constituting groups 1, 2, 13, to 18 are normal or representative elements.
  2. Group 1 elements are named Alkali metals.
  3. Group 2 elements are Alkali Earth Metals.
  4. The elements of group 13 are the Aluminium family.
  5. Group 16 name is Chalcogens.
  6. Elements belong to Group 17 is halogen Group.
  7. The elements of group 18 (zero) are also known as noble or inert gases.
  8. The elements of groups 3 to 12 are transition elements.
  9. In group 3 there are 14 elements just after lanthanum (Z = 57) and another 14 elements just after actinium (Z = 89) which are placed at the bottom of the modern Periodic Table. These are known as lanthanides and actinides respectively and inner- transition elements collectively.

Periodic Table with Groups

ElementsNaturePosition 
s-block elements Metals
  •  1 and 2 group elements
p-block elements Metalloids & non-metals but some of them are metals also.
  •  groups 13 to 18
d-block elements Metals
  • Group 3 to 12
  • 3d series – Sc(21) to Zn (30).
  • 4d series – Y (39) to Cd (48).
  • 5d series – La (57), Hf (72) to Hg (80)
f-block elements Radioactive
  •  Group 3
  • 4f series – Lanthanides – 14 Elements Ce (58) to Lu (71).
  • 5f series – Actinides – 14 Elements Th (90) to Lw (103)

Periodic Table Periods and Groups

The division of Modern Periodic Table into groups and period brings out the similarity and differences and trends in the chemical and physical properties of these elements.

Periods

The horizontal row from left to the right in the periodic table is term as a period.
There are seven periods, each period (except 1st period which starts from hydrogen) starts from alkali metals and ends with the noble gas. In other words, each period starts with a new principal quantum number (n). The filling of electrons in orbitals of elements is as per the Aufbau principle.

Group

18 vertical columns in the Modern Periodic Table previously constituting 16 groups or families and numbered as IA, IIA, IIIB, IVB, VB, VIB, VIIB, VIII, (consisting of three vertical columns of three elements each) IB, IIB, IIIA, IVA, VA, VIA, VIIA, and zero group are now renumbered.
  • Inert gases or noble gases are placed in zero group.
  • The group number is equal to the valency of an element in a group.
  • The 4f and 5 f transition series of elements do not find a proper place in the main table and are placed separately. It is at the bottom of the table in two separate rows of 14 elements. They are known as inner-transition elements.

Periodic Table Metals

There exist different types of metals and are divided into blocks given below:

s-Block Metals
  1. The first two Groups called as s- block elements.
  2. They are present on the left corner in the Modern Periodic Table.
  3. They are soft metals with low melting points and boiling points.
  • Alkali metals. [Li, Na, K, Rb, Cs, Fr]
  • Alkaline earth metals. [Be, Mg, Ca, Sr, Ba, Ra]
p-Block Metals
  1. They Belong to group 13 to 17 in the Modern Periodic Table.
  2. p block present on the right side of the table.
  3. They are less metallic than s block elements.
d-Block Metals
  1. d block belong to group 3rd to 12th.
  2. It’s another name is transitions metal elements.
  3. They are hard metals with high melting points and boiling points.
  4. They show magnetic properties.
f-Block Metals
  1. They are located at the bottom of the table.
  2. They are also termed as Inner transition metal elements.
  3. f block metals belonging to period 5th and  3rd group are named as lanthanide metals.
  4. Metals belonging to the 6th period and 3rd group are actinide metals.


Modern Periodic Table Blocks and Groups


The concept of periodic table blocks was given by Mendeleev. Dmitri Mendeleev published a table of elements, which states that the properties of elements are the periodic function of their atomic masses. With the passage of time, British chemist Moseley established that the fundamental property of elements that determine their physical and chemical properties is the atomic number and not atomic weight as proposed by Mendeleev. This led to a change in the periodic law stated above.

i.e., when elements are arranged in increasing order of atomic numbers, the properties of the elements are repeated after certain intervals

 Blocks – s p d f block elements


Periodic table blocks have much importance in studying properties of elements. Depending upon the type of sub-shell in which their last electron being filled up in the atoms of the elements, the elements are divided into four blocks.

  • The elements of groups 1 and 2 are known as s-block elements since in the atoms of the elements, s- subshell are being filled up.


  • The elements of groups 13 to 18 are p-block elements since in the atoms of these elements p-subshell are being filled up.


  • The transition elements are also called d-block elements because in the atoms of these elements d-subshell are being filled up.


  • The other name of inner-transition elements is f-block elements because, in the atoms of these elements, f subshell is being filled up.

Blocks

Periodic table blocks have much importance in studying the properties of elements. Depending upon the type of sub-shell in which their last electron being filled up in the atoms of the elements, the elements are divided into four blocks.
  • The elements of groups 1 and 2 are known as s-block elements since in the atoms of the elements, s- subshell are being filled up.

  • The elements of groups 13 to 18 are p-block elements since in the atoms of these elements p-subshell are being filled up.

  • The transition elements are also called d-block elements because in the atoms of these elements d-subshell are being filled up.

  • The other name of inner-transition elements is f-block elements because, in the atoms of these elements, f subshell is being filled up.

Elements have been classified into four periodic table blocks (s, p, d, and f) depending upon the type of subshell which receives the last electron.The four periodic table blocks are:

s- block elements

Elements in which the last electron enters in the s-orbitals of the valence shell of their atoms are called s-block elements.
Since s-subshell can accommodate a maximum of 2 electrons, s-block consists of the elements of two groups, namely, group I (alkali metals) and group 2 (alkaline-earth metals). The general electronic configurations of the elements of group 1 and 2 are ns1 and ns2 respectively. These elements are present on the extreme left of the periodic table.
Example: Na:  1s2 ,2s2 ,2p,3s1
  • They are soft metals with low melting points and boiling points.
  • These block elements have low ionization energy and are highly electron positive
  • They are highly reactive and are good reducing agents.
  • s Block elements have low electron affinity and electronegativity
  • These metals and their compounds impart color to the flame.

p- block element

Elements in which the last electron enters in the p-orbitals or subshell of the valence shell are called p-block elements.
 Since p-subshell can accommodate a maximum of 6 electrons, p-block consists of elements of six groups namely, 13, 14, 15, 16, 17 and 18 (except He). The general electronic configuration of p-block elements is ns2 np1-6 where n stands for the outermost shell, p-block elements are present on the extreme right of the periodic table.
Example: O (Z=8) = 1s2 ,2s2 ,2p6.
  • They are gases (e.g., Cl2, F2, etc.). liquids (Br) and solids (Al, Sn, Sulphur, etc.).
  • Have high ionization energy.
  • They are electronegative in nature and this character decreases down a group.
  • These elements are less metallic as compared to s-block elements.
  • Their metallic character increases down a group but decreases across a period.
  • Their reducing character decreases across a period while increases down a group.

d- block elements

Elements in which the last electron enters in the d-orbitals of the penultimate (second last) shell of their atoms are called d-block elements.
These elements consist of groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12. They make up three complete rows of 10 elements and an incomplete fourth row in the periodic table. These elements are placed between s-block and p-block elements. Their general configuration ns1-2 (n-1) d1-10
Example Sc (Z = 21) = 1s. 2s 2p3s2 3p3d1 4s2.
  • They are hard metals with high melting points and boiling points.
  • Show variable valency (oxidation state).
  • Elements show magnetic properties.
  • Elements can act as catalytic agents.
  • Give colored compounds.
  • They form complex compounds.

 f- block elements

Elements in which the last electron enters in the f orbitals of the antepenultimate (third from the last shell) of their atoms are called f-block elements.
f  block consists of two series of 14 elements each, known as lanthanide series and actinide series. These have been placed separately at the bottom of the periodic table. In the lanthanides, 4 f subshell and in actinides 5 f-subshell are being gradually filled up.
General electronic configuration of f block elements is (n–2)f1–14(n–1)d0–1ns2
  • Lanthanides: [Xe]4f1–145d0–16s2
  • Actinides: [Rn]5f1–146d0–17s2
Elements after uranium (atomic number 92) are called transuranic elements since they have been obtained from it through the nuclear reaction.
f-block elements are also called inner-transition elements because they form transition series within transition elements. The atoms of these elements have their three outermost shells incomplete.
  • They are heavy metals with high m.pt. and b.pt.
  • They give color to their compounds.
  • They show variable valency (oxidation state).
  •  These are mostly synthetic elements and are radioactive in nature.

This is all about the Modern Periodic Table.
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