Question

Hydrogen has an electronegativity value between boron and carbon and identical to phosphorus. With this in mind, rank the following bonds in order of decreasing polarity: \(\mathrm{P}-\mathrm{H}\) \(\mathbf{O}-\mathbf{H}, \mathbf{N}-\mathbf{H}, \mathbf{F}-\mathbf{H}, \mathbf{C}-\mathbf{H}\)

Short answer

The ranking of the given bonds based on decreasing polarity is: \(\mathrm{F}-\mathrm{H} > \mathrm{O}-\mathrm{H} > \mathrm{N}-\mathrm{H} > \mathrm{C}-\mathrm{H} > \mathrm{P}-\mathrm{H}\).

Step-by-step solution

Recall the electronegativity values of the given atoms.

To rank the bonds based on polarity, we first need to find the electronegativity values of the involved atoms. Here are the general electronegativity values for the relevant elements using the Pauling scale: - Hydrogen (H): 2.1 - Oxygen (O): 3.5 - Nitrogen (N): 3.0 - Fluorine (F): 4.0 - Carbon (C): 2.5 - Phosphorus (P): 2.1 (same as Hydrogen, as given in the exercise)

Calculate the electronegativity differences for each bond.

Next, we will calculate the electronegativity differences between the atoms in each bond. The larger the electronegativity difference, the more polar the bond will be. 1. P-H: |2.1 - 2.1| = 0 2. O-H: |3.5 - 2.1| = 1.4 3. N-H: |3.0 - 2.1| = 0.9 4. F-H: |4.0 - 2.1| = 1.9 5. C-H: |2.5 - 2.1| = 0.4

Rank the bonds based on electronegativity differences.

Now, rank the bonds in order of decreasing polarity by comparing the electronegativity differences calculated in Step 2. 1. F-H: 1.9 (most polar) 2. O-H: 1.4 3. N-H: 0.9 4. C-H: 0.4 5. P-H: 0 (least polar) So, the correct ranking of the bonds based on decreasing polarity is: \(\mathrm{F}-\mathrm{H} > \mathrm{O}-\mathrm{H} > \mathrm{N}-\mathrm{H} > \mathrm{C}-\mathrm{H} > \mathrm{P}-\mathrm{H}\).

Key concepts

Chemical Bonds

Understanding chemical bonds is essential for grasping how atoms come together to form molecules. At the core of this concept is the idea that atoms bond in ways that allow them to attain a more stable electronic configuration. There are three primary types of chemical bonds: ionic, covalent, and metallic.

Ionic bonds occur between metals and nonmetals and involve the transfer of electrons from one atom to another. This results in the formation of ions, where one atom becomes positively charged (cation) and the other negatively charged (anion). Covalent bonds, on the other hand, involve the sharing of electrons between two nonmetals. The shared electrons allow each atom to achieve a full outer shell, leading to a more stable molecule.

Metallic bonds are found in metals, where electrons are not shared between individual atoms but move freely throughout the entire metal structure. This 'sea of electrons' is what gives metals their characteristic properties such as conductivity and malleability.

Each type of bond has different properties and is determined by factors such as the elements involved and their electronegativity. Understanding the distinction between these bond types is foundational in studying the polarity and behavior of molecules in various chemical contexts.

Polarity of Molecules

The polarity of molecules is a critical factor that influences their physical and chemical properties like solubility, boiling point, and reactivity. A molecule is considered polar if it has a net dipole moment; this is a result of the unequal distribution of electron density across the molecule.

To determine the polarity of a bond within a molecule, we look at the electronegativity difference between the atoms involved. If the difference is significant, the electrons are more attracted to one atom, which becomes partially negative, leaving the other atom partially positive. Nonpolar covalent bonds, in contrast, involve equal sharing of electrons between atoms with similar electronegativities, resulting in no significant charge separation.

A molecule's overall polarity also depends on its shape. Even if a molecule has polar bonds, if the geometry is symmetrical, the dipoles can cancel out, making the molecule nonpolar. In asymmetrical molecules, the dipoles don't cancel, leading to a polar molecule.

Understanding the concept of polarity is vital for predicting how molecules will interact with each other, determining the kind of interactions they may have, and even in predicting the type of solvent that would dissolve them best.

Pauling Scale

The Pauling scale is an invaluable tool in chemistry used to quantify the electronegativity of elements. Developed by chemist Linus Pauling, this scale helps compare the tendency of atoms to attract shared electrons in a chemical bond.

The scale typically runs from around 0.7 for very low electronegative elements like cesium to 4.0 for highly electronegative elements such as fluorine. Hydrogen sits near the middle with a value of 2.1. These values serve as a guide to predict bond types and polarity: the larger the difference in electronegativity between two bonded atoms, the more polar the bond will be.

For example, in the provided exercise, when ranking the bonds from most to least polar, we relied on the Pauling scale to calculate the electronegativity differences. The F-H bond was the most polar due to the largest difference in electronegativity, according to the Pauling scale, while P-H was nonpolar, having no difference as they have the same electronegativity.

This scale is fundamental for students not only to understand bond polarity but also to predict molecular properties and reactivity based on the nature of the chemical bonds present in a molecule.