Overview
This lecture covers the basic structure of matter and atoms, the types of chemical bonds, properties of water, and how these concepts relate to biological systems.
Matter and Atomic Structure
- Matter is anything that has mass and occupies space.
- Atoms are the smallest units of matter, consisting of protons, neutrons, and electrons.
- Protons (positive charge) and neutrons (neutral) are found in the nucleus; electrons (negative) orbit the nucleus.
- Atomic mass is the sum of protons and neutrons; measured in daltons.
- Elements are substances that cannot be broken down by ordinary chemical means.
- The four main elements in living organisms are carbon, hydrogen, oxygen, and nitrogen.
Ions, Isotopes, and Atomic Behavior
- Ions are atoms where protons and electrons are unequal; cations are positive, anions are negative.
- Isotopes are atoms of the same element with different numbers of neutrons; stable isotopes do not decay, radioactive isotopes do.
- Half-life is the time for half of a radioactive substance to decay.
- Valence electrons are those in the outermost energy shell, crucial for bonding.
- The octet rule states atoms tend to fill their outer shell with 8 electrons.
Chemical Bonds and Reactions
- Chemical bonds are attractions that hold atoms together.
- Ionic bonds form between oppositely charged ions.
- Covalent bonds involve sharing two or more valence electrons.
- Electronegativity is an atom's tendency to attract electrons in a bond.
- Polar covalent bonds share electrons unequally, leading to partial charges.
- Chemical reactions transform reactants into products and are influenced by temperature, concentration, and catalysts.
- Redox reactions involve electron transfer; oxidation is loss, reduction is gain.
Molecules, Compounds, and Water
- Molecules are groups of atoms held together stably; compounds are molecules with different elements.
- Water is a polar molecule, leading to hydrogen bonding, cohesion (water-water attraction), and adhesion (water-other polar substances attraction).
Properties of Water
- Water has high specific heat, high heat of vaporization, is less dense as a solid, is a good solvent, organizes nonpolar molecules, and can form ions.
- Surface tension and capillary action in water result from hydrogen bonds.
Acids, Bases, and pH
- The pH scale measures hydrogen ion concentration in a solution.
- Acids increase hydrogen ion concentration; bases decrease it.
- Buffers stabilize pH by releasing or absorbing hydrogen ions; biological buffers usually consist of an acid-base pair.
- Pure water has neutral pH and is colorless, odorless, and tasteless.
Key Terms & Definitions
- Atom — smallest unit of matter
- Ion — charged atom due to unequal protons and electrons
- Isotope — same element, different neutron number
- Cation — positively charged ion
- Anion — negatively charged ion
- Valence electrons — electrons in outer energy level
- Ionic bond — attraction between oppositely charged ions
- Covalent bond — bond formed by sharing electrons
- Electronegativity — atom’s ability to attract shared electrons
- Hydrogen bond — weak attraction involving hydrogen
- Buffer — substance maintaining pH stability
Action Items / Next Steps
- Review properties and examples of chemical bonds.
- Practice identifying ions, isotopes, and types of chemical reactions.
- Study the unique properties of water and their biological significance.