Overview
This lecture introduces atoms, their structure, the particles they contain, and key characteristics used to describe them.
What Are Atoms?
- Atoms are the tiny building blocks that make up all matter.
- Atoms are so small that one million lined up equal the width of a sheet of paper.
- Atoms are often drawn as colored circles to help visualize their structure.
Structure of an Atom
- An atom has a central nucleus containing protons and neutrons.
- Protons (positively charged) and neutrons (neutral) are found in the nucleus.
- Electrons (negatively charged) move rapidly around the nucleus.
Properties of Subatomic Particles
- Protons have a charge of +1; electrons have a charge of –1; neutrons have no charge (0).
- Opposite charges attract: electrons are held near the nucleus by the attraction to protons.
- Neutrons help stabilize the nucleus by holding protons and neutrons together.
Mass of Subatomic Particles
- Protons and neutrons have nearly equal mass, about 1 atomic mass unit (AMU) each.
- Electrons are much lighter, with a mass of about 0.000549 AMU.
- Atomic mass is mostly determined by the number of protons and neutrons; electrons contribute negligibly.
Atom Size and Space
- Most of an atom is empty space; if the nucleus were the size of a grape, electrons would be almost a mile away.
- Electrons move in unpredictable, random paths rather than simple circles.
Describing Atoms
- Atoms are described using characteristics like atomic number (number of protons), mass number (protons + neutrons), and net charge.
Key Terms & Definitions
- Atom — the smallest unit of matter, made of protons, neutrons, and electrons.
- Nucleus — the center of an atom, containing protons and neutrons.
- Proton — positively charged particle in the nucleus, mass ≈ 1 AMU.
- Neutron — neutral particle in the nucleus, mass ≈ 1 AMU.
- Electron — negatively charged particle moving outside the nucleus, mass ≈ 0.000549 AMU.
- Atomic Mass Unit (AMU) — unit of mass used to measure protons and neutrons.
- Atomic Number — number of protons in an atom.
- Mass Number — sum of protons and neutrons in an atom.
Action Items / Next Steps
- Review the concepts of atomic number, mass number, and net charge for further discussion.