Arrange the following elements in the increasing order of electronegativity. Be , F , O , N , Li

The tendency of an atom to attract the electrons of a bond towards itself is called the electronegativity of an atom. The electronegativity of an atom depends on the atomic size. The lower the atomic size, the more the electronegativity of an atom. The atomic size decreases in a period from left to right, therefore, the electronegativity increases. So, the increasing order of electronegativity of the given elements is the following: Li < Be < N < O < F

Write any two demerits of Mendeleev's periodic table.

The demerits of Mendeleev's periodic table are the following: (i) Position of hydrogen- The position of hydrogen is not fixed in Mendeleev's periodic table because hydrogen resembled the properties of both alkali metals and halogens. (ii) Position of isotopes- Mendeleev’s periodic table was based on the increasing order of atomic masses of elements. But isotopes are not included in the periodic table.

Write any two merits of Mendeleev's periodic table.

The merits of Mendeleev's periodic table are the following: (i) Mendeleev arranged the elements very systematically in periods and groups based on the atomic mass of the elements. (ii) Mendeleev predicted the existence of certain elements which were not discovered at that time. He left some gaps in the periodic table for the discovery of new elements.

Write the name of the scientist who has given a triad law for the classification of elements. Explain the law of triad.

Johann Wolfgang Dobereiner, a German scientist has given a triad law for the classification of elements. He made an attempt to arrange the elements with similar properties into groups having three elements each. These groups are called triads. According to Dobereiner triad law, the arithmetic mean of the atomic masses of the first and third elements in a triad would be approximately equal to the atomic mass of the second element in that triad. For example, the triad of alkali metals lithium, sodium, and potassium. The atomic masses of lithium, sodium, and potassium are 6 , 23 and 40 . So, the arithmetic mean = 6 + 40 2 = 46 2 = 23 It is equal to the atomic mass of sodium.

Write the name of the scientist who has given the octave rule for the classification of elements. Explain the octave rule.

John Newlands, an English scientist has given the octave rule for the classification of elements. He rearranges the known elements in the increasing order of their atomic masses and found that every eighth element had similar properties to that of the first element like the octaves of the music that are sa, re, ga, ma, pa, dha, ni, and sa. In the musical octaves, the first and the last notation is the same, same as the properties of every eighth element is the same as that of the first element. Therefore, it is known as Newland's law of octaves.