1. Elements
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Definition: An element is a substance made of only one type of atom.
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There are 92 naturally occurring elements; about 26 are essential for human life.
Common Elements in the Human Body:
| Element | Symbol | Function |
|---|---|---|
| Oxygen | O | Needed for respiration |
| Carbon | C | Forms the backbone of all organic molecules |
| Hydrogen | H | Found in water and organic compounds |
| Nitrogen | N | Found in proteins and DNA |
| Calcium | Ca | Needed for bone and muscle function |
| Iron | Fe | Part of hemoglobin is for carrying oxygen |
2. Atoms
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Definition: The smallest unit of an element that still has its properties.
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Atoms are made of:
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Protons (positive charge, in nucleus)
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Neutrons (neutral charge, in the nucleus)
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Electrons (negative charge, orbit around the nucleus)
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Example:
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A hydrogen atom has:
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1 proton
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0 neutrons
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1 electron
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3. Chemical Bonds
Atoms join together through chemical bonds to form molecules.
Main Types of Bonds:
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Ionic Bonds
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Formed when electrons are transferred from one atom to another.
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Example: NaCl (table salt) → Na⁺ + Cl⁻
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Covalent Bonds
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Formed when atoms share electrons.
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Strong and common in organic compounds.
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Example: H₂O (water) → each H shares electrons with O.
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Hydrogen Bonds
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Weak bonds between hydrogen and other atoms (usually oxygen or nitrogen).
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Important in DNA structure and protein folding.
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Example: Bonds between DNA base pairs (A-T and G-C).
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4. Chemical Reactions
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Definition: Process where chemical bonds are made or broken.
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Reactants → Products
Types of Reactions:
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Synthesis (Anabolism): A + B → AB
Example: Amino acids form proteins. -
Decomposition (Catabolism): AB → A + B
Example: Breakdown of glucose in cells. -
Exchange Reactions: AB + CD → AD + CB
Example: Acid-base neutralization.
Enzymes:
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Enzymes are proteins that speed up reactions.
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Example: Amylase helps break down starch in saliva.
5. Inorganic Compounds of Importance
a) Water (H₂O)
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Makes up 60–70% of body weight.
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Acts as a solvent, helps regulate temperature, and enables transport.
b) Oxygen (O₂)
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Needed for cellular respiration (energy production in mitochondria).
c) Carbon Dioxide (CO₂)
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Waste product of metabolism, removed by the lungs.
d) Salts
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Made of ions (e.g., Na⁺, K⁺, Cl⁻, Ca²⁺).
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Important for nerve impulses and muscle contraction.
6. Organic Compounds of Importance
Organic compounds contain carbon and are usually large and complex.
a) Carbohydrates
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The main source of quick energy.
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Example: Glucose (C₆H₁₂O₆)
b) Lipids (Fats and Oils)
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Long-term energy, insulation, and cell membranes.
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Example: Triglycerides, cholesterol.
c) Proteins
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Made of amino acids.
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Used for structure, enzymes, hormones, and immune response.
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Example: Hemoglobin, insulin.
d) Nucleic Acids
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Store and transmit genetic information.
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DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
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