On a daily basis, we come across countless objects which have some or the other naturally occurring elements in them. From thermometers to the utensils we use, everything around us is made up of different elements. But do you know how these elements have been organised so accurately in the modern periodic table? Class 10 chapter on Periodic Classification of Elements will take us through various important features regarding the arrangement of elements. Our detailed notes on this topic will help you score well in scholastic as well as competitive exams.
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What Led to Classification of Elements?
There are multiple elements, hence, it is impossible to analyze their properties individually. The classification of elements is done to facilitate the study of the elements in an easy way. The periodic classification of elements is the structured grouping of similar elements. It also means separating similar elements from the dissimilar ones. Many scientific discoveries have been performed to separate and classify the elements based on their properties.
Traditional Laws of Periodic Classification of Elements
The periodic classification of elements refers to the tabular arrangement of different elements. The arrangement is made in such a way that each of the elements having similar properties is placed in the same vertical group or column. The significant attempts of periodic table classification mentioned in the chapter are Dobereiner’s triads and Newlands law of octaves. Let’s study them in detail-
Periodic Classification Of Elements: Dobereiner’s Triads
The Dobereiner’s triad classification is based upon the atomic mass of the elements. According to this classification, “When the elements are arranged in the order of their increasing atomic masses, then a group of three different elements having the same properties and characteristics is obtained.” The atomic mass of any middle element of the triad is almost equal to the average atomic masses of the first and third elements. For example- Li (6.9), Na (23), K (39)
Limitations of This Theory
Dobereiner’s Triads theory fails to organize the known elements in the triad form. The limitation of this theory exists even in the case of elements having similar properties.
Periodic Classification Of Elements: Newland’s Law Of Octaves
As per Periodic Classification of Elements, the Newland’s law of octaves states that , “When the elements are arranged in the order of their increasing atomic masses, then the chemical and physical properties of every 8th element of the order have the repetition of the first element’s properties.”
Limitations of This Theory
The Newland’s law of octaves has certain limitations, some of which are mentioned below:
- The law of octaves for the elements is only applicable up to the calcium element (i.e., for lighter elements only)
- As per the theory, elements are adjusted in the same slot having different properties. For example, Co and Ni with Chlorine, Fluorine, Bromine, and Iodine.
- As per the theory, only 56 elements from the periodic classification of elements existed in nature. It also stated that no further elements would be discovered in the future
The theories mentioned above were traditional and did not align well with the present-day discoveries. Hence, the present attempt for the classification of elements is clarified with the following theories.
Mendeleev’s Periodic Table
Mendeleev’s Periodic Table is one of the most important concepts to cover in the chapter on the periodic classification of elements. This theory is based upon the physical and chemical properties of the elements along with their atomic masses. The periodic law says, “The physical or chemical characteristics of the elements are the periodic function of their atomic masses.“
Periodicity and Merits
The repetition of the element’s properties after a fixed interval is known as its periodicity. Every atom has its periodicity. The merits of Mendeleev’s periodic table as per the periodic classification of elements are as follows-
- It has vacant places in the table to provide an exemplary idea for further discovery or the addition of new elements. For example- Eka-silicon, Eka-aluminium
- This table has predicted multiple properties for undiscovered elements on behalf of its position in the table
- It is extremely useful in correcting the irregular atomic masses of few elements
- The noble gases in the table could accommodate without disturbing the table later to the discovery
Limitations Of Mendeleev’s Periodic Table
Limitations of Mendeleev’s periodic table as stated in the chapter on periodic classification of elements-
- It has no fixed position for hydrogen corresponding to the alkali metals or halogens (17th group)
- It has no place for the isotopes, i.e., the position of isotopes is not decided
- No fixed trend in the atomic mass, i.e., the position of a few elements with lower atomic masses is before the elements having a higher atomic mass
Modern Periodic Table
In 1913, Henry Moseley said that the atomic number of any element is more fundamentalistic than its atomic mass. A law has been enacted in the same consideration, which is known as the modern periodic law. Major postulates of this law are as follows-
- The physical and chemical properties of the elements are the periodic function of their atomic number.
- The modern periodic table’s positioning is based upon the atomic number of the elements.
- The atomic number of elements is equal to the number of protons present in its atom.
- The modern-periodic-table has 18 vertical columns (known as a group) and 7 horizontal rows (known as periods).
How to Move in a Periodic Table?
As per the modern periodic law, the movement from groups to period is followed as-
- Upon moving from left to right in the period, the number of shells remains the same
- Upon moving from left to right in a period, the number of valence electrons significantly increases from 1 to 8 in the present elements.
- All the elements of a particular group in the periodic table have a similar number of valence electrons.
We hope that these notes on the periodic classification of elements class 10 must have answered your questions from the chapter. Do you want to know which stream is best for you as per your interests and choices? If yes, then, get in touch with the Leverage Edu experts and they will help you select one through our exclusive psychometric test.