Question

Identify the most electronegative element in each of the following molecules: (a) \(\mathrm{CH}_{2} \mathrm{FCl}\) (b) \(\mathrm{FCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}\) (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) (d) \(\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{Li}\)

Short answer

(a) Fluorine, (b) Fluorine, (c) Oxygen, (d) Oxygen.

Step-by-step solution

Understand Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. In the periodic table, electronegativity usually increases across a period from left to right and decreases down a group. The most common scale for electronegativity is the Pauling scale.

Identify Elements in Each Molecule

List the elements present in each given molecule. For example, in (a) \(\mathrm{CH}_{2} \mathrm{FCl}\), the elements are C (carbon), H (hydrogen), F (fluorine), and Cl (chlorine). Repeat this process for each molecule.

Review Electronegativity Values

Recall the electronegativity values on the Pauling scale for each relevant element: Hydrogen (2.1), Carbon (2.5), Oxygen (3.5), Nitrogen (3.0), Fluorine (4.0), Chlorine (3.0), Bromine (2.8), and Lithium (0.98).

Compare Electronegativity in Molecule (a) \(\mathrm{CH}_{2} \mathrm{FCl}\)

Among the elements H, C, F, and Cl, fluorine has the highest electronegativity value (4.0). Thus, fluorine is the most electronegative element in \(\mathrm{CH}_{2} \mathrm{FCl}\).

Compare Electronegativity in Molecule (b) \(\mathrm{FCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}\)

The elements are F, C, H, Br. Fluorine has an electronegativity of 4.0, which is higher than bromine (2.8), carbon (2.5), and hydrogen (2.1). Hence, fluorine is the most electronegative element in \(\mathrm{FCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}\).

Compare Electronegativity in Molecule (c) \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\)

The elements to compare are H, O, C, N. Oxygen has an electronegativity of 3.5, higher than nitrogen (3.0), carbon (2.5), and hydrogen (2.1), making oxygen the most electronegative in \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\).

Compare Electronegativity in Molecule (d) \(\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{Li}\)

With the elements O, C, H, and Li, oxygen has the highest electronegativity (3.5), much higher than carbon (2.5), hydrogen (2.1), and lithium (0.98). Therefore, oxygen is the most electronegative in \(\mathrm{CH}_{3} \mathrm{OCH}_{2} \mathrm{Li}\).

Key concepts

Pauling scale

As you dive into the world of chemistry, you’ll come across the concept of electronegativity. The Pauling scale is the most widely used tool to measure this property. Developed by Linus Pauling in 1932, it assigns numerical values to the ability of an atom to attract electrons when forming chemical bonds.
The scale is dimensionless and runs from around 0.7 (for the element Francium) up to 4.0 (for Fluorine), the most electronegative element. The Pauling scale allows chemists to predict the behavior of atoms in molecules and their chemical bonding tendencies. Understanding the Pauling scale is crucial because:

• It aids in predicting how elements will interact with each other.
• It helps determine the polarity of bonds, which affects the molecule's physical properties.
• It serves as a guideline for identifying the most electronegative elements, crucial in understanding molecular structures.

Using the Pauling scale, you can compare different atoms within a molecule to determine which one has a stronger pull on shared electrons.

Electronegativity values

Electronegativity values are numerical indicators that provide insights into an element's ability to attract electrons. These values are crucial when it comes to predicting the behavior of molecules because they influence how atoms bond with each other.

On the Pauling scale, each element has an assigned value:

• Fluorine: 4.0 – most electronegative element.
• Oxygen: 3.5
• Chlorine: 3.0
• Nitrogen: 3.0
• Bromine: 2.8
• Carbon: 2.5
• Hydrogen: 2.1
• Lithium: 0.98

Electronegativity values help determine which atom in a molecule will most strongly attract the electron cloud, resulting in asymmetric electron distributions. This difference in electron attraction is what leads to the formation of polar or nonpolar bonds. Larger differences in electronegativity values between atoms typically lead to more polar bonds.

Chemical bonding

Chemical bonding is the process where atoms come together to form molecules. Electronegativity plays a key role in the type of chemical bond that forms between atoms.
The three main types of chemical bonds are:

• Ionic bonds: Formed when there is a large difference in electronegativity, as seen between metals and non-metals. One atom donates an electron to another, creating charged ions.
• Covalent bonds: These occur when two atoms with similar electronegativities share electrons. There's a range of these, including nonpolar covalent bonds (little to no difference in electronegativity) and polar covalent bonds (moderate difference, causing an unequal sharing of electrons).
• Metallic bonds: In metals, a sea of electrons is shared among a lattice of metal atoms, allowing for conductivity and malleability.

Understanding chemical bonding involves examining the electronegativity difference between the atoms involved. This difference affects the molecular structure, physical properties, and the strength of materials. Whether a bond is ionic, covalent, or metallic depends heavily on the electronegativity of the involved elements.