Atoms, Elements, and Ions

Definitions and Structure

An element is the smallest unit that retains the unique chemical properties of a specific type of matter. Elements cannot be broken down into smaller pieces by routine chemical techniques. Atoms are the smallest particles of elements that still maintain all the characteristics of that element.

• Atoms consist of a nucleus, containing protons (positively charged particles) and neutrons (neutral particles). The nucleus is surrounded by electrons (negatively charged particles).

• In the periodic table, elements are arranged based on the number of protons in their nucleus.

Ions

• An ion is an atom that has gained or lost electrons, resulting in a net electrical charge.

• Cations are positively charged ions (loss of electrons).

• Anions are negatively charged ions (gain of electrons).

• Electrolytes are ions found within the body that influence the nervous system, muscle activity, and fluid balance.

Examples of Atoms

Molecular Bonding

Types of Bonds

Atoms join together to form a molecule. Molecules with more than one type of element are called compounds.

• Ionic bonds: Formed when one atom donates electrons to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Covalent bonds: Formed when atoms share pairs of electrons. If the sharing is unequal, the bond is polar covalent (e.g., water); if equal, it is nonpolar covalent.

Bonding Example: Sodium Chloride (NaCl)

Bond Polarity and Water

• Polar covalent bonds occur when electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Nonpolar covalent bonds occur when electrons are shared equally.

Water

Properties and Importance

• Water is a polar solvent due to the unequal sharing of electrons between hydrogen and oxygen.

• Hydrophilic molecules (e.g., salts, sugars) dissolve easily in water.

• Hydrophobic molecules (e.g., fats, oils) do not mix well with water.

• Hydrogen bonds between water molecules contribute to water's unique properties.

• Water composes 60–80% of the human body.

Solutions and Concentrations

• Solute: The substance dissolved.

• Solvent: The substance doing the dissolving (water in living things).

• Solution concentration: The amount of solute dissolved in a solvent per unit of volume.

Dehydration

• Defined as fluid loss of greater than 1% of body weight; can be fatal if severe.

Biological Molecules

Major Classes

1. Carbohydrates

2. Lipids

3. Proteins

4. Nucleic acids

Carbohydrates

• Composed of carbon, hydrogen, and oxygen (C:H:O ratio of 1:2:1).

• Monosaccharides: Simple sugars (e.g., glucose, C6H12O6).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., glycogen).

• Glycogen: Storage form of glucose in animals, especially in the liver.

Lipids

• Composed mainly of carbon and hydrogen; hydrophobic.

• Include fats, oils, phospholipids, and steroids.

• Triglycerides: Most common lipid, made of three fatty acids and a glycerol molecule.

• Saturated fats: No double bonds; solid at room temperature (e.g., butter).

• Unsaturated fats: One or more double bonds; liquid at room temperature (e.g., olive oil).

• Phospholipids: Contain two fatty acid tails and a phosphate group; major component of cell membranes.

• Steroids: Lipids with four carbon rings (e.g., cholesterol, estrogen, testosterone).

Proteins

• Made of long chains of amino acids joined by peptide bonds.

• Functions include:

  • Structural support (collagen in tendons and ligaments)

  • Enzymes (biological catalysts)

  • Transport (e.g., hemoglobin)

  • Movement (muscle proteins)

  • Defense (antibodies)

  • Communication (hormones like insulin)

• Denaturation: Loss of protein structure due to external stress (heat, pH, radiation, etc.), resulting in loss of function.

Nucleic Acids

• Include DNA and RNA.

• Store and transmit genetic information.

• DNA bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G); A pairs with T, C pairs with G.

• RNA bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G); A pairs with U, C pairs with G.

Metabolism

Overview

• Metabolism refers to all chemical operations in the body, requiring nutrients and producing waste.

• Divided into two main processes:

  • Anabolism: Building up of complex molecules from simpler ones (e.g., protein synthesis).

  • Catabolism: Breaking down of complex molecules into simpler ones (e.g., digestion).

• Many anabolic reactions are dehydration synthesis reactions (removal of water to form bonds).

• Many catabolic reactions are hydrolysis reactions (addition of water to break bonds).

Enzymes

Function and Mechanism

• Enzymes are protein molecules that act as biological catalysts, speeding up chemical reactions.

• Enzymes are specific to their substrates (the molecules they act upon).

• Enzyme activity can be inhibited (blocked) or saturated (all active sites filled).

• Enzymes lower the activation energy required for reactions.

ATP and Energy

• Energy from glucose is stored in adenosine triphosphate (ATP).

• ATP is made of a base, a sugar, and three phosphate groups.

• When a phosphate bond is broken, ATP becomes ADP (adenosine diphosphate) and energy is released.

• ATP can be regenerated from ADP by adding a phosphate group.

Key Equations:

• Dehydration synthesis:

• Hydrolysis:

• ATP hydrolysis: