The following observations are made about two hypothetical elements A and B: The A—A and B—B bond lengths in the elemental forms of A and B are 2.36 and 1.94 Å, respectively. A and B react to form the binary compound AB2, which has a linear structure (that is, ∠B-A-B=180°). Based on these statements, predict the separation between the two B nuclei in a molecule of AB2.

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Identify the bond lengths given: A—A is 2.36 Å and B—B is 1.94 Å.

Recognize that AB2 has a linear structure, meaning the angle ∠B-A-B is 180°.

In a linear molecule like AB2, the separation between the two B nuclei is the sum of the bond lengths A—B and B—A.

Assume that the bond length A—B is the average of A—A and B—B bond lengths, as a first approximation.

Calculate the separation between the two B nuclei by adding twice the A—B bond length (since there are two A—B bonds in AB2).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bond Length

Bond length is the average distance between the nuclei of two bonded atoms. It is influenced by the types of atoms involved and the nature of the bond (single, double, etc.). In this case, the bond lengths of A—A and B—B provide insight into the strength and characteristics of the bonds formed in the compound AB2.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. The linear structure of AB2, indicated by the bond angle of 180°, suggests that the two B atoms are positioned directly opposite each other with respect to the A atom, which affects the overall spatial configuration and bond lengths in the compound.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the geometry of molecules based on the repulsion between electron pairs around a central atom. In the case of AB2, the linear arrangement arises because the two B atoms repel each other and the lone pairs or other bonding pairs around A, leading to a straight-line configuration.

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