PERIODIC TABLE Presented by: TEENA KATHPAL Lecturer Pt. J R Govt Polytechnic College Hoshiarpur

PERIODIC TABLE “It is defined as the table in which all the elements are arranged in the order of increasing atomic numbers.” In other words, it classifies all the known elements according to their properties so that the elements with similar properties are placed together in same group while with different properties are separated from each other.

Need of Classification 1. To study the elements in a better way 2. To correlate the properties of the elements. 3. To study relationship between different elements.

HISTORICAL DEVELOPMENT Doebereiner’s Triads: Doebereiner,a German chemist in 1817,made first attempt towards classification. “He arranged the elements having similar properties in a group of three (triad) and showed that the atomic mass of the middle element is arithmetic mean of the atomic masses of the other two elements.”

DOBERIENER’S TRIADS Li 7 Na 7+39/2 46/2 = 23 K 39

Newland law of Octaves In 1865,an English chemist, John Newland observed that “When the elements are arranged in the increasing order of atomis masses,the properties of the every eighth element are similar to first element.”

Newland octaves 1 Li 2 Be 3 B 4 C 5 N 6 O 7 F 8 Na 9 Mg 10 Al 11 Si 12 P 13 S 14 Cl

Mendeleev’s Periodic Table In 1869, a Russian chemist, Dmitri Mendeleev classified the various elements on the basis of a law, called Mendeleev Periodic Law which states that- “ The Physical and chemical properties are the periodic function of their atomic masses.”

CHARACTERISTICS OF MENDELEEV PERIODIC TABLE PERIODS: The horizontal rows in the periodic table are called periods. There are 7 periods in this periodic table numbered from 1 to 7.

GROUPS: The Vertical columns in the periodic table are called groups GROUPS: The Vertical columns in the periodic table are called groups. There are 8 Groups in this periodic table starting from I,II……….VIII. Each group is sub-divided into two groups i.e A and B.So, there are total 16 groups i.e IA IB,IIA, IIB…….. VIIIA and VIIIB and a zero group having noble gases.

MERITS OF MENDELEEV’S PERIODIC TABLE Systematic study of elements: Knowing the properties of one element in a group, the properties of other elements can be easily guessed. Prediction of new elements: Mendeleev left some gaps in the periodic table for undiscovered elements but he predicted the properties of those elements. e.g. Ge and Ga. Correction of Atomic masses: Atomic masses of some elements were corrected by using Mendeleev periodic table. e.g. Gold and Platinum .

Position of Lanthanides Cause of periodicity DEMERITS: Position of Hydrogen Position of Isotopes. Anomolous pairs Position of Lanthanides Cause of periodicity Separation of similar but grouping of dissimilar elements Metals and Non metals

MODERN PERIODIC TABLE In 1942, Moseley did some X-Ray studies and concluded that atomic number is the more fundamental property of an element than its atomic mass. So, classification should be on the basis of atomic number. This formed the basis of Modern Periodic law.

MODERN PERIODIC LAW It states that- “ The Physical and chemical properties are the periodic function of their atomic numbers.”

Features of long form of periodic table or Bohr’s table PERIODS: Seven horizontal rowsin the periodic table are called periods and are numbered as 1,2, 3………., 7.

First period: it contains only two elements i. e First period: it contains only two elements i.e. Hydrogen (Z=1) and Helium (Z=2). Third Period: It also contains eight elements. It starts with Na (Z=11) and ends with Ar (Z=18). First period: it contains only two elements i.e. Hydrogen (Z=1) and Helium (Z=2). Second Period: It contains eight elements. It starts with Li(Z=3) and ends with Ne (Z=10).

Fourth Period: It contains eighteen elements Fourth Period: It contains eighteen elements. It starts with K (Z=19) and ends with Kr (Z=36). Fifth Period: It also contains eighteen elements. It starts with Rb (Z=37) and ends with Xe (Z=54). Sixth Period: It contains 32 elements. It starts with Cs (Z=55) and ends with Rn (Z=86).

The numbers 2,8,8,18,18 and 32 are called magic numbers. Seventh Period: It also contains 32 elements. It starts with Fr (Z=87) and ends with Uuo (Z=118). First three periods containing 2, 8, 8 elements are called Short periods while the next periods i.e 4th, 5th, 6th and 7th periods containing 18, 18, 32 and 32 elements respectively are called long periods. The numbers 2,8,8,18,18 and 32 are called magic numbers.

GROUPS The vertical columns in the periodic table are called groups. There are 18 groups in the periodic table. Group 1 elements are called alkali metals. Group 2 elements are called alkaline earth metals.

Group 18 elements are called noble gases. Group 17 elements are called halogens. Group 16 elements are called chalcogens. group 1 and 2 are present on extreme left and 13 to 18 are present on extreme right side of the periodic table while groups 3 to 12 are present at the middle of periodic table.

Blocks in the periodic table There are four blocks: 1. s-block 2. p block 3. d block 4. f block

S- block elements Last electron enters in s orbital. Involves groups 1 and 2. General electronic configuration of block: ns 1-2

p- block elements Last electron enters in p orbital. Involves groups 13 to 18. General electronic configuration of block: ns 2 np 1-6

d- block elements Last electron enters in d orbital. Involves groups 3 to 12. General electronic configuration of block: ( n-1)d 1-10 ns 0-2

f- block elements ( n-2)f 0-14 ( n-1)d 0-1 ns 2 Last electron enters in f orbital. General electronic configuration of block: ( n-2)f 0-14 ( n-1)d 0-1 ns 2

Lanthanides: The 14 elements after Lanthanum (Z= 57) are called lanthanides i.e from Ce ( Z= 58 ) to Lu ( Z= 71). Actinides: The 14 elements after Actinium (Z= 89) are called actinides i.e from Th ( Z= 90 ) to Lr ( Z= 103).

Representative Elements: The elements of s and p block are collectively called Representative elements. These include group 1 and 2 and 13-18. Transition Elements: The d-block elements are also called Transition elements. Inner transition Elements: The f-block elements are also called Inner transition elements or Rare earth metals.

In addition to this,the elements are also classified into three categories in the periodic table- 1. Metals: On extreme left hand side and constitute 75% of known elements. 2. Non-metals: On extreme right hand side of the periodic table. 3. Metalloids: Which show properties of both metals as well as non metals.

Advantages of long form of periodic table 1. easy to remember and reproduce. 2. based on atomic number which is more fundamental property. 3. position of isotopes has been solved. .

4. position of anomolous pairs has also been explained 5. Position of element is related to its electronic configuration, so cause of periodicity explained. 6. Lanthanides and actinides are placed at the bottom of periodic table.

Defects of long form of periodic table 1. Position of hydrogen is uncertain as it resembles alkali metals as well as halogens. 2. Lanthanides and actinides are not placed in the main body of the periodic table.

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