Overview
This lecture covers Chapter 2: The Chemical Foundation of Life, focusing on atoms, molecules, water's properties, and the importance of carbon in biological systems.
Atoms, Elements, and Subatomic Particles
- Matter has mass, takes up space, and is made of elements.
- Atoms are the smallest units of matter retaining element properties.
- Elements cannot be broken down while maintaining their properties; each is represented by a unique symbol.
- The four most common elements in living organisms are carbon, oxygen, hydrogen, and nitrogen.
- Atoms consist of a nucleus (protons +, neutrons 0) and outer regions (electrons -).
- Protons, neutrons, and electrons are called subatomic particles.
Atomic Number, Mass, and Isotopes
- Atomic number = number of protons in an atom (defines the element).
- Atomic mass = protons + neutrons (measured in atomic mass units, AMU).
- Isotopes are atoms of the same element differing in neutrons (e.g., C-12, C-13, C-14).
- Electrons inhabit specific orbitals, filling from closest to the nucleus outward.
Chemical Bonds and Molecules
- Electrons in the outer "valence" shell participate in bonding.
- Atoms seek full valence shells (octet rule: 8 electrons; 2 for H and He).
- Covalent bonds involve sharing electrons; can be single, double, or triple.
- Ionic bonds involve transfer of electrons, forming charged ions (e.g., NaCl).
- Polar covalent bonds share electrons unequally; nonpolar covalent bonds share equally.
- Hydrogen bonds and van der Waals interactions occur between molecules and are weaker than covalent/ionic bonds.
Properties of Water
- Water makes up 60–70% of the human body and is vital for life.
- Water is a polar molecule, forms hydrogen bonds, and is a universal solvent.
- Ice is less dense than liquid water; water has high heat capacity and resists temperature changes.
- Cohesion (water sticking to itself) enables surface tension; adhesion (sticking to other substances) aids capillary action.
- pH measures acidity/alkalinity; 7 is neutral, below 7 acidic, above 7 basic.
- Buffers help maintain stable pH in organisms.
Carbon and Functional Groups
- Carbon is a key component in all macromolecules (proteins, carbs, lipids, nucleic acids).
- Carbon forms 4 covalent bonds, allowing complex, energy-rich structures (hydrocarbons).
- Isomers have the same formula but different structures (e.g., cis/trans).
- Functional groups give molecules specific properties (e.g., hydroxyl, amino, phosphate).
- Hydrogen bonds stabilize large biological molecules like DNA.
Key Terms & Definitions
- Atom — Smallest unit of matter with element properties.
- Isotope — Atom version with a different number of neutrons.
- Covalent Bond — Chemical bond involving shared electrons.
- Ionic Bond — Bond formed by transfer of electrons between atoms.
- Polar Molecule — Molecule with uneven electron sharing, causing partial charges.
- Cohesion — Attraction between water molecules.
- Adhesion — Attraction of water to other substances.
- Buffer — Substance that stabilizes pH by absorbing/releasing H+ or OH-.
- Functional Group — Group of atoms in a molecule giving characteristic properties.
- Isomer — Molecules with same formula but different structures.
Action Items / Next Steps
- Review definitions for matter, element, proton, neutron, electron.
- Practice distinguishing covalent vs. ionic bonds.
- Be able to explain water’s properties and the role of carbon in macromolecules.
- Prepare for quiz on atomic structure and types of chemical bonds.
- Next reading: Macromolecules (Chapter 3).