Fundamentals of Chemistry and Atomic Structure

• An ion with more protons than electrons carries a positive charge.
• An ion with more electrons than protons carries a negative charge.

Chemical Bonds and Reactions

Atoms rarely exist in isolation; they interact to form more complex structures through chemical reactions. In these reactions, reactants (the starting substances) undergo changes to create products.

Covalent Bonds

One of the most important ways atoms interact is through covalent bonds, which occur when atoms share electrons. Depending on how many electrons are shared, these can be:

• Single covalent bonds: One pair of electrons shared.
• Double covalent bonds: Two pairs of electrons shared.
• Triple covalent bonds: Three pairs of electrons shared.

A classic example is the hydrogen molecule, formed when two hydrogen atoms share electrons via a covalent bond.

Inorganic Compounds and Electrolytes

Chemical substances are broadly categorized into two groups: organic and inorganic. Inorganic compounds generally do not contain carbon-hydrogen bonds. Common examples include water ($H_2O$), oxygen ($O_2$), and carbon dioxide ($CO_2$).

The Role of Electrolytes

A vital subset of inorganic substances are electrolytes. These are substances that dissolve in water to produce positively or negatively charged ions. Because they produce ions, electrolyte solutions can conduct electricity. In the human body, electrolytes are essential for:

• Nerve impulse transmission
• Muscle contractions
• Maintaining fluid balance

Common inorganic ions include Sodium ($Na^+$), Potassium ($K^+$), Calcium ($Ca^{2+}$), and Chloride ($Cl^-$).

Organic Compounds: The Molecules of Life

Organic compounds are molecules that contain carbon and serve as the fundamental building blocks of living organisms. There are four major classes of organic molecules that make up our cells:

1. Carbohydrates (Sugars): Composed of carbon, hydrogen, and oxygen, these serve as primary energy sources. They are categorized as monosaccharides (single sugars like glucose or fructose) or disaccharides (double sugars like sucrose or lactose).
2. Lipids (Fats): Also composed of carbon, hydrogen, and oxygen, lipids are used for long-term energy storage and cell membrane structure. Major types include triglycerides (the most common fat), phospholipids, and steroids.
3. Proteins: Built from amino acids, proteins contain carbon, hydrogen, oxygen, and nitrogen (and sometimes sulfur). They perform a vast array of functions within the cell.
4. Nucleic Acids: Composed of nucleotides, these contain carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are responsible for storing and transmitting genetic information.

Acids, Bases, and the pH Scale

The chemical environment of the body is heavily influenced by the concentration of hydrogen ions ($H^+$). This is measured using the pH scale.

• Acids: Substances that release $H^+$ ions when dissolved in water. Increasing the concentration of $H^+$ ions lowers the pH level.
• Bases: Substances that accept $H^+$ ions or release hydroxide ions ($OH^-$) when dissolved in water. This increases the $H^+$ concentration's opposite effect, raising the pH level.

The pH Scale and Buffers

The pH scale ranges from acidic to basic (alkaline), with a neutral point where the amounts of hydrogen ions and hydroxide ions are equal.

Summary of pH States

• Acidic: High concentration of $H^+$ ions; low pH.
• Neutral: Equal $H^+$ and $OH^-$ ions; pH of 7.
• Basic (Alkaline): High concentration of $OH^-$ ions; high pH.

Because even small changes in pH can be fatal to biological processes, the body utilizes buffers. Buffers are essential molecules that help keep pH stable by neutralizing excess acids or bases.