Overview
This lecture introduces the basic concepts of chemistry, focusing on the structure and significance of atoms, atomic theory, and the roles of subatomic particles in defining elements.
What is Chemistry?
- Chemistry is the science of matter and its transformations, exploring how tiny particles form everything.
- Chemistry bridges physics and biology, explaining life, technology, medicine, and more.
Atomic Theory and Its Confirmation
- Atomic theory states that all matter is made of atoms, tiny indivisible particles.
- A scientific theory is a well-tested explanation, not just a guess.
- Einstein confirmed the existence of atoms in 1905 via mathematical explanation of Brownian motion, observed by Robert Brown in 1827.
Structure of Atoms
- Atoms are composed of protons (positively charged), neutrons (neutral), and electrons (negatively charged, tiny mass).
- Protons and neutrons form the nucleus; electrons surround the nucleus and determine chemical behavior.
Atomic Number, Elements, and Symbols
- The atomic number equals the number of protons and defines the element.
- Elements keep their identity across reactions because their proton count rarely changes.
- Element symbols may derive from Latin (e.g., Ag for silver from "argentum").
Nucleus and Stability
- The nucleus is small, stable, and held together by the strong nuclear force.
- Neutrons prevent protons from repelling each other, stabilizing the nucleus.
Isotopes and Atomic Mass
- Atoms of the same element can have different numbers of neutrons, called isotopes.
- The atomic mass is the weighted average of all isotopes' masses.
- Mass number is the sum of protons and neutrons in an atom.
Key Terms & Definitions
- Atom — The smallest unit of an element, composed of protons, neutrons, and electrons.
- Atomic Number — Number of protons in an atom's nucleus, defining the element.
- Proton — Positively charged subatomic particle in the nucleus.
- Neutron — Neutral subatomic particle in the nucleus.
- Electron — Negatively charged subatomic particle outside the nucleus with tiny mass.
- Nucleus — The central part of an atom containing protons and neutrons.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Relative Atomic Mass — The weighted average mass of an element's isotopes.
- Mass Number — Total number of protons and neutrons in a specific atom.
- Brownian Motion — Random movement of particles in a fluid, evidence for atoms.
Action Items / Next Steps
- Review atomic structure and terminology.
- Prepare for discussion on charge and electron behavior in the next lesson.