Question #e175e

1 Answer
Aug 21, 2017

Depends upon periodic trends. In series, an increase in Electronegativity decreases bond strength, but in Groups (mainly nonmetals) an increase in Electronegativity increases bond energy.


Electronegativity, by definition, is an elements attraction for electron cloud. This is a natural property of an element that depends upon the number of protons in the nucleus and electron energy levels surrounding the element.

For the Main Group Elements, Electronegativity in 'series' increases with increasing atomic number. That is for Row 2 (or any subsequent row) of the periodic table, Electronegativity increases in the order Li < Be < B < C < N < O < F < Ne. Such results in decreasing atomic and ionic radii as atomic number increases. When this series of elements are bonded with another element (in particular the elements C, N, O & F), the bond energy is found to generally decrease in order of C-X > N-X > O-X > F-X. The nuclei in this series demonstrate increasing attraction for electron cloud with increasing atomic number that results in decreasing bond strength.

For elements in a Group or Family, Electronegativity will decrease with increasing atomic number due to the 'shielding effect' due to additional energy levels of electrons surrounding the nucleus. Group VIIA of the Main Group Elements (F, Cl, Br, I) demonstrate a decreasing Electronegativity with increasing atomic number. The same is true in other Families of Elements. When these elements are bonded to another element, the decreasing Electronegativity due to the 'shielding effect' will follow with a decrease in bonding energy as well. For example, it has been shown that the acidity of the Hydrogen Halide family of binary acids increases in strength with decreasing electronegativity of the central halogen element and the decreasing bond energy of the Hydrogen-Halide. That is, the acidity of the Hydrogen Halide acids increase in the order H-F < H-Cl < H-Br < H-I. This is opposite to electronegative effects in a 'periodic series' of elements. The group trend demonstrates decreasing bonding energy with decreasing electronegativity due to increasing size and shielding effect of the element within the specified 'Group'. This acidity trend for the binary halogen acids is known as the 'Hydrogen Halide Paradox' because it is opposite to the 'In Series' trend.