Problem 34 - Chemistry and Chemical Reactivity

Question

For each of the bonds listed below, tell which atom is the more negatively charged. (a) \(\mathrm{C}-\mathrm{N}\) (c) \(\mathrm{C}-\mathrm{Br}\) (b) \(\mathrm{C}-\mathrm{H}\) (d) \(\mathrm{S}-\mathrm{O}\)

Step-by-Step Solution

Answer

(a) N, (b) C, (c) Br, (d) O.

Step 1: Understand Electronegativity

Electronegativity is the tendency of an atom to attract the bonding electrons in a chemical bond. The more electronegative atom attracts the electrons more strongly, becoming slightly negative. Refer to a periodic table to check the electronegativities of the elements involved.

Step 2: Compare Electronegativity for Each Pair

Find the electronegativity values for each pair of atoms involved in the bond: - For \(\text{C-N}\): Carbon (C) has an electronegativity value of 2.55. Nitrogen (N) has an electronegativity of 3.04.- For \(\text{C-Br}\): Carbon (C) is 2.55, and Bromine (Br) is 2.96.- For \(\text{C-H}\): Carbon (C) is 2.55, and Hydrogen (H) is 2.20.- For \(\text{S-O}\): Sulfur (S) is 2.58, and Oxygen (O) is 3.44.

Step 3: Determine the More Electronegative Atom

Based on the comparison of electronegativity values: - In \(\text{C-N}\) and \(\text{C-Br}\), nitrogen and bromine, respectively, are more electronegative and thus more negatively charged.- In \(\text{C-H}\), carbon is more electronegative and more negatively charged.- In \(\text{S-O}\), oxygen is more electronegative and more negatively charged.

Step 4: Finalize Answers for Each Bond

Based on the previous analysis:(a) In the \(\mathrm{C}-\mathrm{N}\) bond, nitrogen (N) is more negatively charged.(b) In the \(\mathrm{C}-\mathrm{H}\) bond, carbon (C) is more negatively charged.(c) In the \(\mathrm{C}-\mathrm{Br}\) bond, bromine (Br) is more negatively charged.(d) In the \(\mathrm{S}-\mathrm{O}\) bond, oxygen (O) is more negatively charged.

Key Concepts

Chemical Bonds

Chemical bonds are the connections that hold atoms together within molecules. There are different types of chemical bonds, such as covalent, ionic, and metallic bonds. Each type of bond has unique characteristics and involves different sharing or transfer of electrons.
A bond can form between two atoms when they share electrons, such as in a covalent bond, or when one atom donates electrons to another, as seen in ionic bonds.

• In a covalent bond, electrons are shared between the atoms, leading to the formation of a molecule.
• Ionic bonds occur when electrons are transferred from one atom to another, resulting in charged ions that attract each other.
• Metallic bonds involve a 'sea of electrons' shared among a lattice of metal atoms.

Understanding chemical bonds helps explain how compounds form and why they have specific properties, like melting points or electrical conductivity.

Periodic Table

The periodic table is a systematic organization of chemical elements in order of increasing atomic number. Each element has its unique characteristics determined by the number of protons, electrons, and neutrons.
The layout of the periodic table helps in understanding various properties of elements, including their electronegativity.

• Elements are arranged in rows, known as periods, and columns called groups.
• Generally, electronegativity increases across a period from left to right.
• It tends to decrease down a group as you move from top to bottom.

Hence, the periodic table not only categorizes elements but also predicts trends in properties like atomic size, electron affinity, and, importantly for our topic, electronegativity. This makes it a powerful tool in predicting how different elements will react with one another.

Electronegativity Values

Electronegativity refers to an atom's ability to attract shared electrons in a bond. Different elements have different electronegativity values, which explain the behavior of atoms in molecules.
Pauling's scale is the most commonly used scale to quantify electronegativity.

• On this scale, fluorine, with an electronegativity of 3.98, is the most electronegative element.
• The level of electronegativity influences whether a bond will be polar or nonpolar.
• Chemical bonds with a significant difference in electronegativity between the two atoms are typically polar.

Electronegativity values are crucial for understanding which atom in a bond will be more negatively charged, based on how the shared electron cloud is skewed towards the more electronegative atom.

Atom Polarity

Atom polarity relates to how the electrons in a molecule are distributed and affects the molecule's dipole moment. When one atom in a bond is more electronegative than the other, it pulls the shared electrons closer.
This creation of partial charges leads to molecular polarity, where one side of the molecule is slightly more negative.

• Molecules with polar bonds have uneven electron distribution.
• Nonpolar molecules have electrons shared more equally between the atoms.
• The difference in atom polarity affects the solubility and reactivity of the substance.

Moreover, understanding atom polarity helps explain phenomena such as hydrogen bonding and molecule interactions. Recognizing atom polarity is essential when predicting molecular shapes and their physical and chemical characteristics.