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Modern Periodic Table

Chemistry Formulas

Introduction to Modern Periodic Table

The periodic table of elements is one of the most powerful icon in science a single document that consolidates much of our knowledge of chemistry.

The periodic table of elements is an important landmark in the history of chemistry.  It is considered as one of the great scientific achievements.  It is difficult to study individually the chemistry of more than one hundred elements known today and their related compounds.  In the 19th century, chemists like Dobereiner, Newlands, Dimitri Mendeleev and Moseley thought of proper classification of elements and did monumental work in analyzing the properties of these elements and classifying them.  Finally we will examine that the physical & chemical properties of elements repeat periodically like the seasons in nature.For More Chemistry Formulas check out Main page of Physics Wallah.

Mendeleev’s Periodic Law

In 1869, Mendeleev, a Russian chemist stated that “The physical and chemical properties of elements are a periodic function of their atomic weights.“  In other words, according to this law, when the elements are arranged in the increasing order of their atomic masses, the elements with similar properties are repeated at regular intervals.  

Mendeleev’s Periodic Table

Mendeleev arranged 63 - 65 elements known at that point of time in the increasing order of their atomic weights in the form of a table, known as Mendeleev’s periodic table and published in 1905.  It is noted that at this time noble gases were not discovered.Mendeleev’s original table consists of eight vertical column (called groups) I-VIII & six horizontal rows (called periods). The group number were indicated by Roman numerals.He placed elements with similar nature in same group with respect to atomic weight.  However

i) At some places the order of atomic weight was changed in order to justify the chemical and physical nature. e.g. Cobalt (at. Wt. = 58.9) is placed before Ni (At. Wt = 58.7)

ii) Some places were left vacant for new elements which were not discovered at that point of time e.g.,  scandium, gallium and  germanium etc., were not known at that time.  He left vacant space for them and named them as eka-boron, eka-aluminium and eka-silicon believing them to be similar to boron, aluminium and silicon respectively.  

iii) The first half of elements were placed in the upper left corner and second half in the lower right corner of each box.  e.g., In 4th period of group I, K is written in the top left corner, while Cu is written in the lower right corner. 

Defects in the Mendeleev’s periodic table

It was a brilliant attempt for the classification of elements but it had certain defects in it.  These defects are described below:

i. Position of hydrogen:  In Mandeleev’s periodic table, position of hydrogen was not made clear.  i.e., It can be placed either in group – I or VII.

ii. Separation of chemically similar elements:  Certain elements which appear to be chemically similar like Cu and Hg, Au and Pt etc., have been placed in separate groups.

iii. Grouping of chemically dissimilar elements: Certain chemically dissimilar elements have been grouped together in the Mendeleev’s periodic table. e.g., Cu, Ag and Au have no resemblance with alkali metals (Li, Na, K etc),but these have been grouped together in group I. 

iv. Inversion in periodic table:  Certain pairs of elements had to be placed in the reverse order of atomic masses in order to confirm the periodic law.  e.g., Co (58.9) has been placed before Ni (58.7) and Ar (39.9) has been placed before K (39.1) etc.

v. Position of Isotopes:  No separate places were given to isotopes.

vi. Position of lanthanides and actinides:  Lanthanide & actinide were not given places in periodic table.  From these anomalies, atomic weight does not appear to be a good basis for the periodic classification of elements.

About Modern Periodic Table

i) It was proposed by Moseley

ii) Modern periodic table is based on atomic number 

Characteristic of Modern Periodic Table

i) It consists of 9 vertical columns called groups are families i.e., i to viii  + 0 group and 7 horizontal series (rows) are called periods.

ii) Inert gases were introduced by Ramsay

Extended form or Long form of Periodic Table

i) It is the most widely accepted form of periodic table.

ii) It is based on modern periodic law i.e., atomic number and electronic configuration.

iii) It was constructed by Neils Bohr and proposed by Rang, Werner, Bury and others.  It is also known as Bohr’s periodic table (1920).

iv) It consists of 18 groups and 7 periods.

v) In this modified long form of periodic table (based on IUPAC -1984 recommendation) the groups have been numbered from left as group 1 to group 18.  

vi) The number of IA, IIA, IIIB - - - 0, in the Bohr’s design has been dropped. 

General Characteristics of Modern Periodic Table

i) The 18 vertical columns of long form of periodic table, are called groups.

ii) Some groups have typical names.  e.g,.

a) Elements of group 1 are called alkali metals.

b) Elements of group 2 are called alkaline earth metals

c) Elements of group 15 are called pnicogens

d) Elements of group 16 are called chalcogens

e) Elements of group 17 are called halogens

f) Elements of group 18 are called noble gases.

g) Elements of group 11 are called coinage metals.

iii) The 7 horizontal rows or columns of long form of periodic table are called periods. i.e., 

a) first period : It contains two elements i.e., H & He. It is called shortest period

b) second period : It contains eight elements  i.e.  Li to Ne.  It is called short period.  The elements of second period are also known as bridge elements.

c) third period :It also contains 8 elements i.e. Na to Ar and known as short period.  The elements of this period are also known as typical elements.

d) fourth period : It contains 18 elements, K to Kr and this is called long period.

e) fifth period : It  has also 18 elements, Rb to Xe.  This is called long period.

f) sixth period : It has 32 elements, Cs to Kr.  This period is a longest Period.

g) seventh period : It is an incomplete period which has 29 – elements, Fr to Uuo.

iv) The elements of group 1, 2 & 13 to 17 are called main group elements.  These are also called as representative or normal elements.

v) The element of group 3 to 12 are called transition elements.

vi) Elements with atomic number 58 to 71 are called lanthanides whereas the elements with atomic number 90 to 103 are called actinides.  These elements are also known as f-block elements or inner-transition elements.

vii) Lanthanides (4f-series) and actinides (5f-series) are placed in two separate rows below the main periodic table to avoid unnecessary side wise expansion of the periodic table.    

Advantage of Modern Periodic Table

1. It is based on more fundamental property i.e. atomic number and electronic configuration.

2. It completely separates metals and non – metals.

3. Due to separation of two sub groups, dissimilar elements do not fall together.

4. It correlates the position of elements with their electronic configuration clearly.

5. The completion of each period is more logical.

6. Periodicity in properties can be easily visualized.

7. The greatest advantage of this periodic table is that this can be divided into four blocks namely s,p,d and f-blocks elements.

8. This arrangement of elements is easy to remember and reproduce.

9. It removes the anomalies of Mandeleev’s periodic table i.e., K39 precides Ar40. 

Defects of Modern Periodic Table

1. Position of Hydrogen is not fixed till now

2. Position of helium is not fully justified as its EC justifies it to be included in the s – block.

3. Position of lanthanides and actinides has not been given inside the table.

4. It does not reflect the exact distribution of electrons among all the orbitals of the atoms of all the element.

Modern Periodic Table and Electronic Configuration of elements

Many different forms of a periodic classification of the elements have appeared since the 1871 table by Mendeleev. Each table was designed to point up the various trends and relationship, which its author considered most significant. From the literally hundreds of tables which have been proposed, perhaps the most popular and easily reproduced periodic table is the conventional extended or long form, which is shown in table.

i) Each period starts with an alkali metal whose outermost electronic configuration is ns1.

ii)  Each period ends with a noble gas of outermost electronic configuration ns2np6 except He. The electronic configuration of He is 1s2.

iii)  The number of elements in a period is equal to the number of necessary electrons to acquire ns2np6 configuration in the outermost shell of first element (alkali metal) of the period. First period contains two elements.

v) The number of elements in each period may be determined by the number of electrons in a stable configuration as under 

modern periodic table

Electronic basis for the periodic classification

With a better understanding of the part that the electron plays great role in the properties of the elements, a corresponding understanding of the periodic system came about.On the basis of electronic configuration, the elements may be divided into four groups.

i) s-Block elements  

a)  These are present in the left part of the periodic table.

b)  These are group IA and IIA elements. 

c)  In these elements last electron is filled in the s subshell.

d)  Electronic configuration of valence shell is ns1-2 (n = 1 to 7).

ii)  p-block elements 

a)  These are present in right part of the periodic table.

b)  These constitute the groups IIIA to VIIA and zero group i.e. group 13 to 18 of the periodic table.

c)  The last electron is filled in p subshell of valence shell.

d)  The electronic configuration of valence shell is nsnp1-6 (n = 2 to 7).

e)  ns2np6is stable noble gas configuration. The electronic configuration of He 1s2.

f) Prior to noble gas group, there are two chemically important groups of non-metals. 

These are halogens (group 17) and chalcogens (group 16).

iii)  d-Block elements

a)  These are present in the middle part of the periodic table (between s & p block elements. 

b)  These constitute IIIB to VIIB, VIII, IB and IIB i.e, 3 to 12 groups of the periodic table.

c)  All are metals.

d)  The last electrons fill in (n – 1)dsubshell.

e)  The outermost electronic configuration is (n-1)d1-10 ns1-2 (n = 4 to 7).

f)  There are three series of d-block elements as under: 

3d series – Sc(21) to Zn (30)

4d series – Y (39) to Cd (48)

5d series – La (57), Hf (72) to Hg (80)

iv) f-Block elements  

a)  These are placed separately below the main periodic table.

b)  These are mainly related to IIIB i.e. group 3 of the periodic table. 

c)  There are two series of f-block elements as under: 

4f series – Lanthanides – 14 Elements from Ce (58) to Lu (71)

5f series – Actinides – 14 Elements from Th (90) to Lr (103)

d)  The last electron fills in (n – 2) f subshell.

e)  Their outermost electronic configuration is (n-2)f1-14 (n-1)s2 (n-1)p6 (n-1)d0-1ns2  (n = 6 and 7).

Important Points About Modern Periodic Table

1.Each period starts with an alkali metal and ends with a noble gas.

2.Based on the differentiating electrons, the elements are classified into s, p, and f blocks.

3.Electronic configuration of s-block elements is ns1 & ns2.

4.Electronic configuration of p-block elements is ns2 np1 to ns2np6.

5.Electronic configuration of d-block elements or transition elements is (n-1)d1-10 ns1-2.

6.Electronic configuration of f-block elements or inner transition elements is (n-2) f1-14 (n-1)0-1 ns2.

7.Based on number of incomplete shells the elements are classified into inert gases, representative elements, transition elements.

8.Electronic configuration of representative elements is ns1 to ns2np5.

9.Electronic configuration of inert gases or noble gases is ns2np6.  (except He)

10.Atomic size increases from top to bottom in a group and decreases from left to right in a period.

11.Cations are smaller and anions are larger than its corresponding atoms of the elements.

12.For isoelectronic species (ions), the size decreases with, increase of nuclear charge or atomic number.

13.Ionization potential decreases from top to bottom in a group and increases from left to right in a period.

14.Elements with half filled and completely filled electronic configuration having high ionization potentials.

15.Metals having low ionization potential while non-metals having high ionization potentials.

16.Electron affinity decreases from top to bottom in a group and increases from left to right in a period.

17.Elements with half filled and completely filled electronic configuration having zero electron affinity.

18. Electronegativity decreases from top to bottom in a group and increases from left to right in a period.

Questions Based on Modern Periodic Table

Online Test Based on Modern Periodic Table

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