Problem 8 - Biology: The Unity and Diversity of Life

Question

Atoms share electrons unequally in a(n) _______ bond. a. ionic b. hydrogen c. polar covalent d. nonpolar covalent

Step-by-Step Solution

Answer

Polar covalent bonds involve unequal sharing of electrons.

Step 1: Understanding Bond Types

Different types of chemical bonds exist based on how atoms share or transfer electrons. In an **ionic bond**, electrons are transferred from one atom to another, resulting in charged ions. A **hydrogen bond** is a weak interaction between a hydrogen atom bonded to a more electronegative atom and another electronegative atom. **Covalent bonds** involve sharing electrons; these include **polar** and **nonpolar covalent bonds**.

Step 2: Defining Polar Covalent Bond

In a **polar covalent bond**, the electrons shared between two atoms are not equally shared. This happens because one atom is more electronegative than the other, pulling the shared electrons closer to it, creating a partial negative charge on one atom and a partial positive charge on the other.

Step 3: Distinguishing From Other Bond Types

It is important to differentiate the behavior of electron sharing: - **Ionic bonds** involve transfer rather than sharing. - **Nonpolar covalent bonds** involve equal sharing of electrons. - **Polar covalent bonds** involve unequal sharing due to differences in electronegativity, leading to a dipole moment. - **Hydrogen bonds** are not caused by unequal sharing of electrons.

Step 4: Choosing the Correct Option

Given the explanation above, option c. **polar covalent** bond is the correct answer, as it matches the description of a bond where electrons are shared unequally.

Key Concepts

Chemical Bonds

Chemical bonds are the forces that hold atoms together in a compound. Understanding them is crucial for grasping how molecules form and interact. There are several categories of chemical bonds, primarily:

• **Ionic Bonds**: These occur when one atom donates electrons to another, resulting in attraction between oppositely charged ions.
• **Covalent Bonds**: In these bonds, atoms share electron pairs. Covalent bonds are further classified into polar and nonpolar types.
• **Hydrogen Bonds**: While not a bond in the traditional sense, these are weak attractions involving a hydrogen atom bonded to a more electronegative atom, like oxygen or nitrogen, and another electronegative atom nearby.

To understand why atoms bond, consider the **octet rule**. Most atoms strive to have eight electrons in their outermost shell, which gives them a stable electron configuration. Bonds enable them to achieve this lastingly, either by electron sharing or transfer.

Electronegativity

Electronegativity is a chemical property that refers to the tendency of an atom to attract a bonding pair of electrons. This concept is pivotal in determining how electrons are shared between atoms in a molecule.

In the context of covalent bonds:

• When two atoms have equal or very similar electronegativity values, they share electrons equally, resulting in a **nonpolar covalent bond**.
• When there is a difference in electronegativity between the two atoms, electrons are shared unequally, creating a **polar covalent bond**.

Electronegativity increases across a period from left to right in the periodic table and decreases from top to bottom in a group. Highly electronegative atoms, like fluorine, oxygen, and nitrogen, pull electrons more strongly toward themselves. This uneven sharing gives rise to the characteristics associated with polar covalent bonds.

Dipole Moment

In polar covalent bonds, the uneven sharing of electrons between atoms leads to the formation of a dipole moment. But what exactly is a dipole moment? It's a measure of the charge separation in a molecule. When one atom attracts electrons more strongly due to its higher electronegativity, that atom becomes partially negative, and the other becomes partially positive.

The dipole moment (9) is calculated by the product of the charge (
) and the distance (9) between the charges: \[\mu = \delta \times d\]A molecule with a significant dipole moment is considered polar, with distinct positive and negative sides. Molecules like water exhibit this property effectively, possessing unique physical properties like a high boiling point and surface tension due to their dipole interactions.

In essence, the presence of a dipole moment in a molecule significantly influences how it interacts with other molecules and its environment.