(i) During the process of ionization, the electron to be removed from beryllium atom is a \(2s\)-electron, whereas the electron to be removed from boron atom is a \(2p\)-electron. Now, \(2s\)-electrons are more strongly attached to the nucleus than \(2p\)-electrons. Therefore, more energy is required to remove a \(2s\)-electron of beryllium than that required to remove a \(2p\)-electron of boron. Hence, beryllium has higher \(\triangle_iH\) than boron.
(ii) In nitrogen, the three \(2p\)-electrons of nitrogen occupy three different atomic orbitals. However, in oxygen, two of the four \(2p\)-electrons of oxygen occupy the same \(2p\)-orbital. This results in increased electron-electron repulsion in oxygen atom. As a result, the energy required to remove the fourth \(2p\)-electron from oxygen is less as compared to the energy required to remove one of the three \(2p\)-electrons from nitrogen. Hence, oxygen has lower \(\triangle_iH\) than nitrogen.
Fluorine contains one electron and one proton more than oxygen. As the electron is being added to the same shell, the increase in nuclear attraction (due to the addition of a proton) is more than the increase in electronic repulsion (due to the addition of an electron). Therefore, the valence electrons in fluorine atom experience a more effective nuclear charge than that experienced by the electrons present in oxygen. As a result, more energy is required to remove an electron from fluorine atom than that required to remove an electron from oxygen atom. Hence, oxygen has lower \(\triangle_iH\) than fluorine.
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Top Questions on Electronic Configurations Of Elements And The Periodic Table
Classification of Elements & Periodicity in Properties
Since many elements were being discovered in the 19th century and the study of these elements individually was proving difficult, classification of elements was made necessary.
Classification by Johann Dobereiner - German chemist Johann Dobereiner classified certain elements on the basis of their similar properties in the groups of continuing - three elements each. These groups were called ‘triads’. In every triad, the atomic weight of the middle element was equal to the average of the atomic weights of the first and third elements.
Newlands Law of Octaves - The elements were arranged in increasing order of their atomic weights and found that every 8th element shows similarity with the 1st element.
Mendeleev’s Periodic Table - The arrangement of all 63 elements in rows or columns in order of their atomic weight was made by Mendeleev. He left some space for corresponding elements in his periodic table which were not even discovered till then. Although he predicted the properties of those elements through his periodic classification of elements.
Modern Periodic Law - The properties of the elements of the modern periodic law are periodic functions of their atomic numbers.
