The iodine monobromide molecule, IBr, has a bond lengthof 249 pm and a dipole moment of 1.21 D. (a) Which atom ofthe molecule is expected to have a negative charge?

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Identify the atoms in the IBr molecule: iodine (I) and bromine (Br).

Recall that the dipole moment is a measure of the separation of positive and negative charges in a molecule.

Understand that the dipole moment points from the positive to the negative charge.

Consider the electronegativity of the atoms: Bromine (Br) is more electronegative than iodine (I).

Conclude that the more electronegative atom, bromine (Br), will have a partial negative charge, while iodine (I) will have a partial positive charge.

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Key Concepts

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

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. In the case of IBr, iodine (I) is less electronegative than bromine (Br), meaning that Br will attract the shared electrons more strongly, leading to a partial negative charge on the bromine atom.

Dipole Moment

The dipole moment is a vector quantity that represents the separation of positive and negative charges in a molecule. It is calculated as the product of the charge and the distance between the charges. In IBr, the dipole moment of 1.21 D indicates that there is an uneven distribution of electron density, confirming that one atom carries a partial negative charge.

Bond Polarity

Bond polarity refers to the distribution of electrical charge over the atoms joined by the bond. In IBr, the difference in electronegativity between bromine and iodine results in a polar covalent bond, where bromine becomes partially negative and iodine partially positive, leading to the overall dipole moment observed in the molecule.

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