Question

Predict the direction of polarization of the following bonds, considering only the relative electro negativity of the atoms involved. \(\mathrm{C}-\mathrm{H}\) \(\mathrm{B}-\mathrm{H} ;\) \(\mathrm{N}-\mathrm{Br}\) \(\mathrm{I}-\mathrm{Cl}\)

Short answer

In the C-H bond, the direction of polarization is from H to C, with a partial positive charge on H and a partial negative charge on C. In the B-H bond, the direction of polarization is from B to H, with a partial positive charge on B and a partial negative charge on H. In the N-Br bond, the direction of polarization is from Br to N, with a partial positive charge on Br and a partial negative charge on N. In the I-Cl bond, the direction of polarization is from I to Cl, with a partial positive charge on I and a partial negative charge on Cl.

Step-by-step solution

Determine electronegativity values

First, let's find the electronegativity values for the atoms involved in the bonds. This information can be found using a periodic table or reference material. The electronegativity values on the Pauling scale for the atoms involved are: C: 2.55 H: 2.20 B: 2.04 N: 3.04 Br: 2.96 I: 2.66 Cl: 3.16

Predict the direction of polarization for C-H bond

In the C-H bond, carbon has an electronegativity of 2.55 and hydrogen has an electronegativity of 2.20. Since carbon is more electronegative than hydrogen, the direction of polarization will be from H to C. Hence, the C-H bond will have a partial positive charge on the hydrogen atom and a partial negative charge on the carbon atom.

Predict the direction of polarization for B-H bond

In the B-H bond, boron has an electronegativity of 2.04 and hydrogen has an electronegativity of 2.20. This time, hydrogen is more electronegative than boron. Therefore, the direction of polarization will be from B to H. Hence, the B-H bond will have a partial positive charge on the boron atom and a partial negative charge on the hydrogen atom.

Predict the direction of polarization for N-Br bond

In the N-Br bond, nitrogen has an electronegativity of 3.04 and bromine has an electronegativity of 2.96. Since nitrogen is more electronegative than bromine, the direction of polarization will be from Br to N. Hence, the N-Br bond will have a partial positive charge on the bromine atom and a partial negative charge on the nitrogen atom.

Predict the direction of polarization for I-Cl bond

In the I-Cl bond, iodine has an electronegativity of 2.66 and chlorine has an electronegativity of 3.16. Since chlorine is more electronegative than iodine, the direction of polarization will be from I to Cl. Hence, the I-Cl bond will have a partial positive charge on the iodine atom and a partial negative charge on the chlorine atom.

Key concepts

Chemical Bonds

Chemical bonds are the attractive forces that hold atoms together in compounds. There are three main types of chemical bonds: ionic, covalent, and metallic. Ionic bonds form when electrons are transferred from one atom to another, resulting in positively and negatively charged ions. Covalent bonds occur when atoms share one or more pairs of electrons, and metallic bonds involve a 'sea' of delocalized electrons shared among many metal atoms.

In the realm of covalent bonds, the sharing of electrons between atoms can be equal or unequal, leading to the formation of nonpolar or polar covalent bonds, respectively. The degree to which electrons are shared equally or unequally is influenced by a property of atoms known as electronegativity, which is a measure of an atom's ability to attract and hold onto electrons within a chemical bond.

Polar Covalent Bonds

Polar covalent bonds are formed between two atoms with different electronegativities. The atom with the higher electronegativity will attract the shared electrons more strongly, leading to a partial negative charge on this atom, while the other atom acquires a partial positive charge. This separation of charges creates a dipole moment in the bond, with electrons being more likely found around the more electronegative atom.

Understanding the concept of bond polarization is crucial for predicting molecular properties such as solubility, melting and boiling points, and reactivity. For example, water (H2O) is a polar molecule due to the polar covalent bonds between hydrogen and oxygen, which leads to its ability to dissolve many ionic substances as well as other polar molecules.

Periodic Table Electronegativity

Electronegativity values are typically found on the periodic table and are a fundamental property that reflects how strongly an atom can attract electrons. These values increase from left to right across a period as the number of protons increases and the electrons are drawn closer to the nucleus. They also tend to decrease down a group, as valence electrons are farther from the nucleus and more shielded by the inner layers of electrons.

The most commonly used scale to measure electronegativity is the Pauling scale, named after chemist Linus Pauling. It is important to keep in mind that electronegativity values are not absolute and only provide an indication of an atom's relative tendency to attract electrons when forming a bond. Yet, these values are indispensable tools for chemists to predict bond polarity, molecular structure, and the behavior of molecules in chemical reactions.