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Classification of Elements and Periodic Table

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Classification of Elements

Dobereiner Triads

  1. Dobreiner created groups of three elements whose physical and chemical properties were similar. These are called Dobereiner triads.
  2. In this group, the atomic weight of the middle element was almost equal to the average of the atomic weight of the remaining two elements and the properties were also between the properties of both elements.
  3. For example lithium, sodium, and potassium.

 

Newland’s Octave Law

  1. John Newland arranged the elements in ascending order of atomic mass.
  2. The elements arranged by them are the first hydrogen and the last element thorium.
  3. The number of elements in Newland’s table is 56.
  4. He explained that the property of the eighth element is similar to the property of the first element.
  5. He compared it to the octave of music and hence he called it the principle of octave.

 

Mendleaf’s Periodic Table

  1. Mendleaf arranged the elements in ascending order of atomic mass.
  2. The theory of Mendeleev’s periodic table holds that the properties of elements are a recurring function of their atomic mass. 
  3. In Mendeleev’s periodic table, the vertical column is called the group and the horizontal rows are periods.

 

Modern Periodic Table

  1. Modern Periodic Table is given by Henry Mozley.
  2. The theory of the modern periodic table is that the properties of elements are a recurring function of their atomic number.
  3. The classification obtained by arranging the elements in ascending order of their atomic numbers is called the modern periodic table.
  4. The modern periodic table has 18 vertical columns that belong to a group and 7 horizontal rows called periodic.
  5. The elements of s-block is called alkaline and alkaline soil metals.
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  6. The element of P-block is called the principal element.
  7. The element of the d-block is called the transition element.
  8. The elements of the f-block are of the differential transition element.

 

Atomic radius

  1. The distance between the nucleus and the electron present in the outermost shell of an atom is called the atomic radius.
  2. Atomic number increases from left to right in a single period, so the number of protons in the nucleus increases. For this reason, the nuclear attraction force on the electron of the outermost shell is more, so the value of the atomic radius decreases.
  3. The atomic number increases when moving from top to bottom in the same class, the number of shells also increases and the value of effective nuclear charge also decreases, so the atomic radius decreases.

 

Electronegativity

  1. Atomic size decreases from left to right in a single row, due to this electronegativity of the elements increases.
  2. When moving from top to bottom in the same group, the value of electronegativity decreases as the atomic size increases.
  3. Fluorine has the highest electronegativity.

 

Valency

The number of electrons present in any element determines the valency of that element.

 

Atomic Size

 

Metallic and Non-Metallic Properties

  1. The element’s metallic properties increase when moving from top to bottom in the same group.
  2. There is a decrease in the metallic property of an element when moving from left to right in a single period.
  3. That is, the left part in the periodic table is the metallic element while the right part in the periodic table contains the non-metallic element.
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