Question

Bond length decreases with (1) increase in size of the atom (2) increase in the number of bonds between atoms (3) decrease in the number of bonds between atoms (4) decrease in bond angle

Short answer

(2) increase in the number of bonds between atoms

Step-by-step solution

Analyze Each Option

Carefully read and understand each option given to determine how it affects bond length.

Evaluate Option 1

Consider the effect of the increase in the size of the atom. Larger atoms tend to increase the bond length due to their larger atomic radius, so bond length does not decrease with an increase in size.

Evaluate Option 2

Evaluate the effect of an increase in the number of bonds between atoms. An increase in the number of bonds (single to double to triple bond) generally results in shorter bond lengths due to increased bond strength.

Evaluate Option 3

Consider the effect of a decrease in the number of bonds between atoms. A decrease in the number of bonds (triple to double to single bond) would result in a longer bond length.

Evaluate Option 4

Think about the effect of a decrease in bond angle. While bond angles can affect molecular shape, they do not have a direct effect upon bond length. This option is not related to the decrease in bond length.

Conclusion

Based on the evaluations, the increase in the number of bonds between atoms correlates with a decrease in bond length.

Key concepts

Atomic Size

Atomic size plays a critical role in determining the bond length between atoms. When the size of an atom increases, its atomic radius also grows. This larger size means that the distance between the nuclei of bonded atoms is longer. Therefore, larger atoms tend to have longer bond lengths. This relationship is crucial to understand because it helps explain why smaller atoms, with shorter radii, tend to form shorter bonds. For instance, a bond involving Hydrogen atoms (which are smaller) will be shorter than one involving larger atoms like Iodine.

Number of Bonds

The number of bonds between two atoms significantly impacts the bond length. When atoms form multiple bonds (like double or triple bonds), the bond length decreases. This phenomenon occurs due to the increase in bond strength that comes with more shared electrons. Generally, single bonds are the longest, double bonds are shorter, and triple bonds are the shortest. This principle can be seen in molecules like Ethene (with a double bond) having shorter bonds compared to Ethane (with a single bond). The increased overlapping of orbitals in multiple bonds pulls the atoms closer together, reducing the bond length.

Bond Angle

While bond angles are critical to the overall shape of a molecule, they do not directly influence bond length. The bond angle is the angle formed between three atoms across at least two bonds. This parameter is vital for the geometry and spatial arrangement of a molecule. For example, in a tetrahedral molecule like Methane, the bond angles are approximately 109.5 degrees. While altering these angles can affect the molecule's 3D structure, it does not alter the actual distance between two bonded atoms, meaning the bond length remains unchanged.

Bond Strength

Bond strength is a crucial factor that correlates with bond length. Stronger bonds are typically shorter because the strong attraction between the bonding electrons pulls the nuclei closer together. For example, a triple bond is stronger and shorter than a double bond, which in turn is stronger and shorter than a single bond. Bond strength is influenced by the number of shared electrons and the effective nuclear charge holding the electrons in the bonded atoms. As bond strength increases, bond length decreases because the bonded atoms are held tighter together.