Overview
This lecture introduces the basics of atoms, atomic theory, and the structure of the atomic nucleus, laying the groundwork for understanding chemistry.
Chemistry: The Science of Stuff
- Chemistry studies how three particles—protons, neutrons, electrons—combine in countless ways to make all matter.
- Chemistry bridges physics (abstract) and biology (practical) by explaining the nature of substances.
- At its core, chemistry provides insights into life, technology, medicine, and the environment.
Atomic Theory and Atomic Structure
- The idea that all matter is made of atoms was once controversial but is now well established.
- “Theory” in science means a well-tested set of ideas, not a mere guess.
- Albert Einstein mathematically proved the existence of atoms in 1905 by explaining Brownian motion.
- Brownian motion: Pollen grains jiggle randomly in water due to collisions with tiny particles (atoms/molecules).
- The word “atom” comes from Greek, meaning “indivisible,” though atoms can be split (as in nuclear reactions).
Subatomic Particles
- Atoms are composed of protons (positive charge, heavy), neutrons (neutral, heavy), and electrons (negative charge, very light).
- Protons and neutrons are found in the nucleus (center of the atom); electrons orbit around the nucleus.
- Electrons are responsible for chemical reactions and bonding.
Atomic Number, Mass Number, and Isotopes
- The atomic number is the number of protons and determines the element (e.g., silver always has 47 protons).
- The chemical symbol (e.g., Ag for silver) often comes from Latin names.
- Nuclei are stable and unchanged in chemical reactions; electrons are more dynamic.
- Neutrons stabilize the nucleus by offsetting repulsion between protons.
- Isotopes are atoms of the same element with different numbers of neutrons.
- The mass number is the total number of protons and neutrons in the nucleus.
- Relative atomic mass is the weighted average of all isotopes found in nature.
Writing Atomic Information
- Atomic notation includes the chemical symbol, atomic number (protons), mass number (protons + neutrons), and charge (number of electrons).
Key Terms & Definitions
- Atom — The smallest unit of an element, made up of protons, neutrons, and electrons.
- Proton — A positively charged particle in the nucleus.
- Neutron — A neutral particle in the nucleus that stabilizes protons.
- Electron — A negatively charged particle orbiting the nucleus; enables chemical reactions.
- Atomic Number — The number of protons in an atom, which defines the element.
- Mass Number — The total number of protons and neutrons in an atom’s nucleus.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Relative Atomic Mass — Weighted average mass of all naturally occurring isotopes of an element.
- Brownian Motion — Random movement of particles suspended in a fluid, evidence of atoms.
Action Items / Next Steps
- Review atomic symbols, atomic numbers, and mass numbers for familiar elements.
- Prepare questions about atomic structure for class discussion.