Overview
This lecture covers Chapter 2: The Chemical Context of Life, focusing on basic chemistry concepts crucial for understanding cellular biology, atomic structure, elements, molecules, chemical bonds, and their relevance to life processes.
Matter and Elements
- Matter is anything that takes up space and has mass; all organisms are made of matter.
- Elements are substances that cannot be broken down by chemical reactions; compounds are substances of two or more elements in fixed ratios.
- Emergent properties arise when elements form compounds (e.g., sodium + chlorine = table salt).
- About 25 elements are essential for life; carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter.
Atoms and Subatomic Particles
- Atoms are the smallest unit retaining an element's properties, consisting of protons (positive), neutrons (neutral), and electrons (negative).
- Protons and neutrons are in the atomic nucleus; electrons form a cloud around the nucleus.
- Atomic number = number of protons; mass number = protons + neutrons.
- Isotopes are atoms with varying numbers of neutrons; radioactive isotopes decay and are used in radiometric dating.
Electron Arrangement and Periodic Table
- Electrons have potential energy based on their distance from the nucleus, existing in shells and orbitals.
- First shell holds 2 electrons; second and third shells hold up to 8 each.
- Valence electrons are in the outermost shell and determine chemical behavior.
- Periodic table columns group elements by number of valence electrons; rows correspond to number of electron shells.
Types of Chemical Bonds
- Atoms form bonds to achieve full valence shells—noble gases already have full shells and are inert.
- Covalent bonds involve sharing electrons; can be single, double, or triple, depending on pairs shared.
- Polar covalent bonds involve uneven sharing due to differences in electronegativity, leading to partial charges (e.g., water).
- Nonpolar covalent bonds involve equal sharing (e.g., hydrogen gas, methane).
- Ionic bonds form when electrons are transferred, creating oppositely charged ions (e.g., NaCl).
- Hydrogen bonds are weak interactions between partial charges of polar molecules (important in water).
Chemical Reactions and Properties
- Chemical reactions involve making and breaking bonds; reactants are converted to products.
- Chemical equilibrium is reached when forward and reverse reactions occur at the same rate.
- Water is a good solvent for polar and charged substances; nonpolar molecules like oils do not mix with water.
Key Terms & Definitions
- Element — substance that cannot be broken down chemically.
- Compound — substance of two or more elements in a fixed ratio.
- Atom — smallest unit of an element.
- Isotope — atom with same protons but different neutrons.
- Valence electrons — electrons in outermost shell.
- Covalent bond — sharing of electron pairs between atoms.
- Polar molecule — molecule with unequal electron sharing and partial charges.
- Nonpolar molecule — molecule with equal electron sharing.
- Ionic bond — attraction between oppositely charged ions.
- Hydrogen bond — weak bond between partially positive and negative regions.
- Electronegativity — atom’s attraction for electrons in a bond.
- Cation — positively charged ion.
- Anion — negatively charged ion.
- Oxidation — loss of electrons.
- Reduction — gain of electrons.
Action Items / Next Steps
- Review atomic structure diagrams and periodic table organization.
- Practice drawing Lewis structures for simple molecules.
- Read Chapter 3: Water and Life.