Atoms in Biology - Notes
Atoms are the fundamental units of matter that combine to form the molecules and compounds
essential to life. Here's an overview of their relevance in biology:
1. Structure of an Atom
● Nucleus:
● Contains protons (positively charged) and neutrons (neutral).
● Accounts for most of the atom's mass.
● Electron Cloud:
● Electrons (negatively charged) orbit the nucleus in energy levels or shells.
● The arrangement of electrons determines chemical properties and reactivity.
2. Atomic Number and Mass
● Atomic Number:
● Number of protons in an atom.
● Determines the element (e.g., Carbon = 6, Oxygen = 8).
● Atomic Mass:
● Total number of protons and neutrons.
● Example: Carbon's atomic mass ≈ 12.
3. Isotopes
● Atoms of the same element with different numbers of neutrons.
● Example: Carbon-12 and Carbon-14.
● Biological Relevance:
● Radioisotopes (e.g., Carbon-14) are used in dating fossils and medical imaging.
4. Electron Configuration and Bonds
● Electrons occupy energy levels (shells) around the nucleus.
● Valence Electrons:
● Electrons in the outermost shell.
● Determine an atom's ability to form bonds.
● Atoms achieve stability by filling or emptying their valence shells, often through bonding.
5. Types of Chemical Bonds
1. Ionic Bonds
● Formed when electrons are transferred between atoms.
● Example: Sodium chloride (NaCl).
2. Covalent Bonds:
● Formed when atoms share electrons.
● Single, double, or triple bonds based on shared pairs of electrons.
● Example: Water (H₂O), Carbon dioxide (CO₂).
3. Hydrogen Bonds:
● Weak bonds between a hydrogen atom and an electronegative atom (e.g.,
oxygen or nitrogen).
● Example: Between water molecules.
4. Van der Waals Interactions:
● Weak, transient attractions between molecules due to temporary charge
fluctuations.
6. Elements Essential to Life
● Four key elements make up 96% of living organisms:
○ Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).
● Others include:
○ Phosphorus (P), Sulfur (S), Calcium (Ca), Potassium (K), Iron (Fe),
etc.
7. Biological Molecules and Atoms
● Organic Compounds:
○ Contain carbon and form the backbone of life.
○ Example: Carbohydrates, proteins, lipids, nucleic acids.
● Inorganic Compounds:
○ Do not contain carbon-hydrogen bonds.
○ Example: Water (H₂O), salts, minerals.
8. Atoms in Water: The Solvent of Life
● Water's unique properties arise from its atomic structure:
○ Polar Molecule: Oxygen is electronegative, creating a partial negative
charge, while hydrogen has a partial positive charge.
○ Forms hydrogen bonds, leading to:
■ High cohesion and adhesion.
■ High specific heat capacity.
■ Excellent solvent for ions and polar molecules.
5.
