Define Periodic Classification of Elements in Chemistry

Updated on Feb. 6, 2021 07:21 PM IST by Lakshmi Arya

Periodic Classification of Elements:--

  1. Matter around us is present in the form of elements, compounds and mixtures.
  2. Elements are substances containing atoms of only one type eg. Na, Mg, Au etc.
  3. There are 118 elements known to us. All these have different properties.
  4. Out of these 118, only 98 are naturally occurring.

NEED FOR PERIODIC CLASSIFICATION:--
Elements were classified so that they could be studied easily and in an organised manner. The earliest attempt to classify the elements resulted in grouping the then known elements as metals and non-metals. Later further classifications were tried out as our knowledge of elements and their properties increased.

DOBEREINER's TRAIDS :-
In the year 1817, Dobereiner, a German chemist, tried to arrange the elements with similar properties into groups. When elements were arranged in the order of increasing atomic masses, groups of three elements (known as triads), having similar chemical properties were obtained. The atomic masses of the middle element of the triad was roughly the average of the atomic masses of the other two elements.

NEWLAND'S LAW OF OCTAVES :-
Newland arranged the then known elements in the order of increasing atomic masses and found that the properties of every 8th element is similar to that of the 1st element. He compared this to the octaves found in music and called it the 'Law of Octaves'. For example, the properties of lithium (Li) and sodium (Na) were found to be the same.

Total Views: 473

Related FAQs

Q. Write down three elements that show Dobereiner's triad.

Ans: The traid consisting of lithium (Li), sodium(Na) and potassium(K) with the respective atomic masses 6.9, 23.0 and 39.0. The average of the atomic masses of Li and K is 22... read more

Q. Write down the two drawbacks of Newland's Law of Octaves.

Ans: It was applicable upto calcium (for lighter elements only). Properties of new discovered elements did not fit into the Law of Octaves. To fit elements into his table, Newlands put eve... read more

Q. Can following groups of elements be classified as Dobereiner's triad ?
(i) Na, Si, Cl (ii) Be, Mg, Ca
(Atomic mass of Be-9, Na-23, Mg-24, Si-28, Cl-35, Ca-40). Justify your answer.

Ans: (i) Na, Si, Cl :---No, because all these elements do not have similar properties. Although the atomic mass of Si is average of atomic masses of Na and Cl (ii) Be, Mg, Ca :--- Ye... read more

Q. What are the properties of a periodic table?

Ans: Atomic radius increases down a group because as we move along a group the atomic number increases and the  number  of  shells  also  increases  and  the  distan... read more

Q. An element has atomic number 17. To which group and period does it belong to?

Ans: 2,8,7  is  the  electronic configuration of the element whose atomic number is 17.  As it has 7 valence electrons. So Its  belongs to 17th group and 3rd period.... read more

Q. Out of Li and K, which will have stronger metallic character and why?

Ans: As we move down the group, metallic character increases while going from left to right across a period, metallic character decreases. So, K (Potassium)  will  have  more  metallic&... read more

Q. Why are H, Li, Na and K placed in group 1?

Ans: They all have one electron in valence orbit, their valency is one, So they are placed in group 1.... read more

Q. Write the number of horizontal rows in the modern periodic table. What are these rows called?

Ans: There are 7 horizontal rows in the modern periodic Table. These rows are called periods.... read more

Q. Out of the three elements P, Q and R having atomic numbers 11, 17 and 19 respectively, which two elements will show similar properties and why?

Ans: The electronic configuration of P,Q,and R are as given below:-- P(11):-   2, 8, 1 Q(17):-   2, 8, 7 R(19):-   2, 8, 8, 1 The outer shell electronic configuration of P ... read more

Q. Write the formula which is used to determine the maximum number of electrons that a shell can accommodate.

Ans: Formula  which  is  used  to  determine  the  maximum  number  of  electrons  that  a  shell  can  accommodate. 2n2, where... read more