Question

In each of the following diatomic molecules, which end of the molecule is positive relative to the other end? a. hydrogen fluoride, HF b. chlorine monofluoride, ClF c. iodine monochloride, ICl

Short answer

In each diatomic molecule, the positive end relative to the other end is as follows: a. In hydrogen fluoride (HF), the hydrogen (H) end is positive relative to the fluorine (F) end. b. In chlorine monofluoride (ClF), the chlorine (Cl) end is positive relative to the fluorine (F) end. c. In iodine monochloride (ICl), the iodine (I) end is positive relative to the chlorine (Cl) end.

Step-by-step solution

Find out the electronegativity values of the involved atoms.

We can look up electronegativity values from a periodic table or a reference book. The following are the electronegativity values for the atoms involved: - Hydrogen (H): 2.1 - Fluorine (F): 3.98 - Chlorine (Cl): 3.16 - Iodine (I): 2.66

Determine the positive end of hydrogen fluoride (HF).

In a HF molecule, we have a bond between hydrogen (H) and fluorine (F). Comparing their electronegativities, we find that fluorine is more electronegative than hydrogen. When these two atoms form a bond, the more electronegative fluorine will attract the electrons more, causing a partial negative charge to form on the fluorine end. As a result, the hydrogen end will have a partial positive charge, making the hydrogen end of HF positive relative to the fluorine end. Answer for (a): In hydrogen fluoride (HF), the hydrogen (H) end is positive relative to the fluorine (F) end.

Determine the positive end of chlorine monofluoride (ClF).

In a ClF molecule, we have a bond between chlorine (Cl) and fluorine (F). Comparing their electronegativities, we find that fluorine is more electronegative than chlorine. When these two atoms form a bond, the more electronegative fluorine will attract the electrons more, causing a partial negative charge to form on the fluorine end. As a result, the chlorine end will have a partial positive charge, making the chlorine end of ClF positive relative to the fluorine end. Answer for (b): In chlorine monofluoride (ClF), the chlorine (Cl) end is positive relative to the fluorine (F) end.

Determine the positive end of iodine monochloride (ICl).

In an ICl molecule, we have a bond between iodine (I) and chlorine (Cl). Comparing their electronegativities, we find that chlorine is more electronegative than iodine. When these two atoms form a bond, the more electronegative chlorine will attract the electrons more, causing a partial negative charge to form on the chlorine end. As a result, the iodine end will have a partial positive charge, making the iodine end of ICl positive relative to the chlorine end. Answer for (c): In iodine monochloride (ICl), the iodine (I) end is positive relative to the chlorine (Cl) end.

Key concepts

Chemical Bonding

Understanding chemical bonding is crucial for making sense of how atoms come together to form molecules. At the heart of chemical bonding is the concept of electrons being shared or transferred between atoms to achieve stability, often likened to the completion of an atom's outer shell. Electronegativity is a key player in this process, as it influences the type of bond that forms between atoms.

There are three primary types of chemical bonds: ionic, covalent, and metallic. Ionic bonds occur when electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions. Covalent bonds, on the other hand, involve the sharing of electrons between atoms. Metallic bonds are found in metals, where electrons are free to move around a lattice of positive ions.

In the case of diatomic molecules like HF, ClF, and ICl, we're dealing with covalent bonds. However, because the atoms involved have different electronegativities, the electron sharing is unequal. This leads to the development of partial charges and, consequently, the creation of a polar covalent bond—where one end of the molecule has a slight positive charge while the other end has a slight negative charge.

Dipole Moment

The dipole moment is a measure that represents the polarity of a molecule, indicating the direction and magnitude of the charge separation within the molecule. It's a vector quantity, meaning it has both a direction and a size, and is usually reported in Debye units. A molecule with a dipole moment is referred to as a polar molecule.

The direction of the dipole moment points from the positive to the negative end of the molecule. The magnitude of the dipole moment depends on two factors: the amount of charge separation and the distance between the charges. For instance, in HF, the dipole moment would point towards fluorine because it holds a partial negative charge while hydrogen has a partial positive charge.

Calculating the Dipole Moment

If you were to calculate the dipole moment, you would take the product of the charge difference (in this case, the partial charges on the atoms) and the distance between the centers of the positive and negative charges. The greater the electronegativity difference and the more polar the bond, the higher the dipole moment. This can assist in predicting molecular behavior in various environments, such as in electric fields or during intermolecular interactions.

Partial Charge

Partial charge is a concept used to describe the uneven distribution of electron density in a polar covalent bond. The more electronegative atom will draw shared electrons closer to itself, resulting in that atom acquiring a partial negative charge (denoted as \( \delta- \)) and the less electronegative atom adopting a partial positive charge (denoted as \( \delta+ \)). The concept of partial charges is integral to explaining not only molecular polarity but also intermolecular forces and reactivity.

The degree of partial charge that an atom maintains is influenced by the difference in electronegativity between the bonding atoms. For example, in HF, ClF, and ICl, fluorine carries a more significant partial negative charge than hydrogen, chlorine, and iodine, respectively, due to fluorine's higher electronegativity.

Understanding partial charges helps us rationalize why molecules have distinct geometries, boiling points, solubilities, and chemical reactivities. It also underlies the essential interactions in more complex molecules, like those found in biological systems, and is key to understanding molecular recognition and reaction mechanisms.