Chemical Bonds, Water, and pH in Anatomy & Physiology

Chemical Bonds and Water

Types of Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules. The type of bond determines the molecule's properties and behavior in biological systems.

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other. Example: NaCl (table salt).

• Polar Covalent Bonds: Electrons are shared unequally between atoms, leading to partial positive and negative charges within the molecule. Example: Water (H2O).

• Nonpolar Covalent Bonds: Electrons are shared equally between atoms, resulting in no significant charge separation. Example: O2 (oxygen gas), H2 (hydrogen gas).

Example: Water is an example of a polar covalent molecule. The oxygen atom is more electronegative than hydrogen, so electrons spend more time around oxygen, creating a partial negative charge on oxygen and partial positive charges on hydrogens.

Comparison of Polar and Nonpolar Covalent Bonds

Bond Type	Electron Sharing	Example	Charge Distribution
Nonpolar Covalent	Equal	H2, O2	No partial charges
Polar Covalent	Unequal	H2O	Partial positive and negative charges

Additional info: The polarity of water is essential for its role as a universal solvent in biological systems, allowing it to dissolve many ionic and polar substances.

pH and Hydrogen Ions

The pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity. The scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acidic solutions: pH < 7, high H+ concentration (e.g., stomach acid, lemon juice).

• Neutral solutions: pH = 7 (e.g., pure water).

• Basic (alkaline) solutions: pH > 7, low H+ concentration (e.g., bleach, ammonia).

Formula:

$\text{pH} = -\log_{10}[\text{H}^+]$

Example: If the concentration of hydrogen ions is $1 \times 10^{-7}$ M, then pH = 7 (neutral).

Effect of Adding Hydrogen Ions

Adding hydrogen ions (H+) to a solution will lower the pH, making the solution more acidic.

• Key Point: Increasing [H+] decreases pH; decreasing [H+] increases pH.

• Application: The body tightly regulates blood pH (normally 7.35–7.45) because even small changes can disrupt cellular processes.

pH Scale Table

Substance	pH Value	Acidity/Basicity
Stomach acid	1–2	Extremely acidic
Lemon juice	2	Acidic
Vinegar	3	Acidic
Pure water	7	Neutral
Baking soda	9	Basic
Bleach	13	Extremely basic

Additional info: The logarithmic nature of the pH scale means that each unit change represents a tenfold change in hydrogen ion concentration.