Question

24. Which of the following statements is true? the bond order decreases, the bond strength increases, and the bond length increases s the bond order increases, the bond strength increases, and the bond length decreases b. A c. As the bond order increases, the bond strength decreases, and the bond length decreases d. As the bond order decreases, the bond strength decreases, and the bond length decreases e. None of the above is true 25. In which pair of compounds do both compounds have polar covalent bonds? Assume the electronegativity of each element is different from other elements. a. F2 and HF b. HF and KCI CO and H2 d. CO and NO e. More than one of the above 26. The trend in electronegativity values and the periodic table is as follows a. Electronegativity values decrease from left to right and increase from top to bottom b. Electronegativity values decrease from left to right and decrease from top to bottom c. Electronegativity values increase from left to right and increase from top to bottom. d. Electronegativity values increase from left to right and decrease from top to bottom

Answer 1

24. The relationship between bond order, bond energy(or bond strength) and bond length is described in option b. The bond length, which is the average distance between nuclei of two bonded atoms in a molecule, decreases with multiplicity of the bond ( Multiplicity increases the bond order). Bond strength is defined as the energy required to break one mole of bonds of that type in a substance and it indicates stability of a bond.

For eg: C-C has a bond order of 1, bond strength= 347kJ/mol and bond length= 1.54 $\AA$

C=C has a bond order 2, bond strength=619kJ/mol and bond length =1.34 $\AA$

C $\equiv$ C has bond order 3, bond strength = 837kJ/mol and bond length = 1.20 $\AA$

25. If a covalent bond is formed between two dissimilar atoms, the bond formed is said to be polar covalent bond. In such case, one of the atoms generally has a greater tendency to attract electrons towards itself(i.e. more electronegative).The electron pair is therefore pulled closer to that atom.This unsymmetric distribution of electronss leads to partial charge separation (For eg, in HF, Fluorine has partial negative charge and hydrogen end has partial positive charge). For given options, option b and d have polar covalent bonds, therefore correct answer is option e

26. The electronegativity generally increases on moving across a period from left to right. This is primarily due to decrease in atomic size and increase in effective nuclear charge. As a result of increase in effective nuclear charge, the attraction for the electron increases.

Electronegativity generally decreases from top to bottom in a group as atomic size increases and the bonding electrons become away from the nucleus.

Correct option is d.