To find screening effect constant following steps should be followed. Screening effect constant is denoted by letter σ. Screening Effect Constant (Slater’s Rule): The magnitude of the screening effect depends on the number of electrons in the inner shells. Due to this, there is a decrease in the force of attraction between the electrons in the valence shell and the nucleus. This effect is known as the screening effect. While there is repulsion between the valence electrons and the electrons present in the inner shells. The electrons in the valence shell are attracted by the positively charged nucleus. This effect is observed in an atom having more electrons and particularly more electron shells. There is a gradual change in physical properties due to an increase in atomic size which is due to the start of a new energy level. In a group, valence shell configuration is the same, hence chemical properties in a group remain the same. They follow the general trend of periodicity. These properties include screening effect, atomic number, atomic radii, ionic radii, ionization enthalpy, electron gain enthalpy (electron affinity), electronegativity, etc. In a period due to the gradual change in electronic configuration across the period from member to member, there is a gradual change in periodic property across the period. Thus the distribution of electrons in the outermost (valence) shell is the cause of periodicity.
Thus the elements with similar configuration recur at regular intervals in the periodic table, the similar properties also recur in the periodic table. All these elements have similar properties with definite gradation (increase or decrease). We can observe the characteristic configuration of the ns2np5 valence shell. The following table gives the electronic distribution of the halogen family (Group – 17). In a particular group, all elements show a similar electronic distribution in the valence shell and hence they show similar physical and chemical properties. This distribution of electrons in the outermost shell is important because it influences the physical and chemical properties of that element. The distribution of electrons in the outermost shell is called the valence shell of an atom. The physical and chemical properties of an element depend upon the distribution of electrons in the various shells of an atom. These properties are indirectly dependent on their electronic configuration.Īll such properties which are directly or indirectly dependent on the electronic configuration of the elements are called atomic properties. Properties such as melting point, boiling point, the heat of fusion, heat of vaporization, density, atomic volume, etc., are collective properties of a group of atoms. These properties are directly dependent on their electronic configuration. Properties such as atomic and ionic radii, ionization enthalpy, electron gain enthalpy, valency, screening effect, effective nuclear charge, and electronegativities are the properties of individual atoms.
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