Question

In each of the following molecules, which end of the molecule is negative relative to the other end? a. carbon monoxide, \(\mathrm{CO}\) b. iodine monobromide, IBr c. hydrogen iodide, HI

Short answer

a. In carbon monoxide (CO), the negative end is Oxygen (\(\mathrm{O}\)). b. In iodine monobromide (IBr), the negative end is Bromine (\(\mathrm{Br}\)). c. In hydrogen iodide (HI), the negative end is Iodine (\(\mathrm{I}\)).

Step-by-step solution

Electronegativity values

First, let's find the electronegativity values of the elements involved in each molecule. You can find these values in a periodic table or chemistry textbook. Here are the electronegativity values we need: Carbon (C): 2.55 Oxygen (O): 3.44 Iodine (I): 2.66 Bromine (Br): 2.96 Hydrogen (H): 2.20

Determine the negative end of carbon monoxide, CO

In CO, we have a Carbon atom and an Oxygen atom. Comparing their electronegativity values, we can see that Oxygen is more electronegative than Carbon (3.44 > 2.55). This means that in CO, the Oxygen atom is the negative end of the molecule relative to Carbon.

Determine the negative end of iodine monobromide, IBr

In IBr, we have an Iodine atom and a Bromine atom. Comparing their electronegativity values, we can see that Bromine is more electronegative than Iodine (2.96 > 2.66). This means that in IBr, the Bromine atom is the negative end of the molecule relative to Iodine.

Determine the negative end of hydrogen iodide, HI

In HI, we have a Hydrogen atom and an Iodine atom. Comparing their electronegativity values, we can see that Iodine is more electronegative than Hydrogen (2.66 > 2.20). This means that in HI, the Iodine atom is the negative end of the molecule relative to Hydrogen. To summarize: a. In carbon monoxide (CO), Oxygen is the negative end of the molecule. b. In iodine monobromide (IBr), Bromine is the negative end of the molecule. c. In hydrogen iodide (HI), Iodine is the negative end of the molecule.

Key concepts

Molecular Polarity

Molecular polarity refers to the distribution of electrical charge across a molecule. This concept fundamentally divides molecules into polar and non-polar. The polarity of a molecule depends on two key factors:

• The shape of the molecule
• The difference in electronegativity between its bonded atoms

In simple terms, electronegativity is the ability of an atom to attract shared electrons in a bond towards itself. When one atom is significantly more electronegative than another, it will attract electrons closer, creating a slight electrical "pull".
As a result, more electronegative atoms become partially negative, while less electronegative atoms become partially positive. This translated difference results in the polar nature of a molecule.
Polar molecules have a region (or end) that carries a partial negative charge, balanced by a region carrying a partial positive charge. It's like having tiny magnets inside the molecule, creating a distinct positive and negative end. This is what we see in the molecules Carbon Monoxide (CO), Iodine Monobromide (IBr) and Hydrogen Iodide (HI).

Chemical Bonding

Chemical bonding is the glue that holds atoms together in molecules. Understanding the type of bond between atoms is essential to grasp the molecule's properties and behavior. There are primarily two main types of chemical bonding:

• Covalent Bonding
• Ionic Bonding

**Covalent Bonding**
This occurs when atoms share electrons. Depending on the difference in electronegativity between the bonded atoms, covalent bonds may be polar or non-polar. In polar covalent bonds like those in CO, IBr, and HI, electrons are unequally shared, creating a dipole moment that can lead to molecular polarity. **Ionic Bonding**
In contrast, ionic bonding involves the transfer of electrons from one atom to another, leading to the formation of ions. This type of bonding creates strong electrostatic forces between oppositely charged ions, resulting in typically higher melting and boiling points compared to covalent compounds. Covalent bonds are the key players in the molecular structures of CO, IBr, and HI, with shared electrons playing a crucial role in balancing even though they result in polarity differences due to electronegativity disparities.

Dipole Moment

The dipole moment is an important concept that measures the polarity of a chemical bond or molecule. Imagine it as a direction and magnitude indicator of the electrical charge separation within the molecule. Dipole moments occur due to the geometric arrangement and electronegativity differences in atoms. The dipole moment is expressed in Debye units and is a vector, meaning it has both direction and magnitude. When it comes to molecules like CO, IBr, and HI, the electrons are drawn more towards the atom with higher electronegativity. This results in a dipole, depicted as an arrow pointing from the positive to the negative end.
Here's why dipole moments are significant:

• They help in predicting the physical properties of molecules, like boiling and melting points.
• They provide insight into the solubility of compounds in different solvents, crucial for reactions and life-science processes.
• The larger the dipole moment, the more polar the molecule, potentially affecting how it interacts with other molecules.

Understanding the dipole moment equips chemists and students with the ability to predict and explain the behavior and reactivity of molecules in various chemical environments.