Periodic classification of elements online mcq quiz
Periodic classification of elements boostup points
Early Models
➤ Dobereiners’s Triads
★ He found that when elements are arranged into groups of three in the order of their increasing atomic mass, the atomic mass of the element; which comes in the middle; is the arithmetic mean of rest of the two.
★ On this basis, he arranged three elements in one group which is known as ‘Triad’.
★ This arrangement of elements is known as Dobereiner’s Triads.
➤ Limitation of Dobereiner’s Triads
★ Dobereiner could find only three such triads and he could not even put all the elements known at that time in his triads.
★ The rules of Dobereiner’s triads could not be applied to the elements which had very low or high atomic mass Early Models
➤ Newlands’ Law of Octaves
★ Newlands found that every eighth element has similar physical and chemical properties when they are arranged in increasing order of their relative masses.
★ This law is known as Newlands’ Law of Octaves which states that "any given element will exhibit analogous behavior to the eighth element following it in the table".
★ In musical notes, every eighth note produces similar sound. Because of this; Newland’s classification of elements was popularly known as just Octaves.
➤ Limitation of Newlands’ Octaves
★ Newlands’ Octaves could be valid up to calcium only
★ Newlands’ Octaves was valid for lighter elements only.
★ It appears that Newlands did not expect the discovery of more elements than 56 which were discovered till his time.
★ Iron; which has similar property as cobalt and nickel, was placed far from them.
★ Cobalt and nickel were placed in the group with chlorine and fluorine in spite of having different properties.
➤Merits of Mendeleev’s Periodic Table
★ Mendeleev left some blank spaces in his periodic table in order to place the elements having similar properties in the same group.
★ Prediction for the elements to be discovered in future.
➤ Limitation of Mendeleev’s Periodic Table
★Position of Hydrogen
★ Position of Isotopes
➤Modern Periodic Classification
Modern Periodic Law states that the properties of elements are the periodic function of
their relative atomic masses.
★ Elements are arranged in order of their increasing atomic numbers.
★ The vertical columns are known as groups and horizontal columns are known as periods; in the modern periodic table.
★ There are 18 groups and 7 periods in the modern periodic table.
➤Limitations of Modern Periodic Table
★ Position of Hydrogen
Trends in Modern Periodic Table
Metallic Character
➤ Increases from top to bottom in a group.
➤ Decreases from left to right in a period.
Atomic Radius
➤ Increases from top to bottom in a group.
➤ Decreases from left to right in a period.
Electronegativity
➤Decreases from top to bottom in a group.
➤ Increases from left to right in a period.
Ionization Energy
➤ Decreases from top to bottom in a group.
➤ Increases from left to right in a period
Electron Affinity
➤ Decreases from top to bottom in a group.
➤ Increases from left to right in a period
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