Overview
This lecture introduces the structure of atoms, the particles they are made of, how atoms form ions, and how elements are identified using the periodic table.
Structure of the Atom
- All matter is made of tiny particles called atoms.
- Atoms have a central nucleus surrounded by electrons orbiting in shells.
- The nucleus contains protons and neutrons packed tightly together.
- Most of an atom's volume is empty space between the nucleus and electrons.
Subatomic Particles
- Protons and neutrons each have a relative mass of 1; electrons are much lighter (about 1/2000 the mass).
- Protons have a positive charge (+1), neutrons have no charge (0), and electrons have a negative charge (-1).
- The number of protons equals the number of electrons in a neutral atom, balancing the charge.
Atomic Size and Scale
- Atoms have a radius of about 0.1 nanometers.
- The nucleus is tiny compared to the atom, about 10,000 times smaller in width.
Ions
- Atoms can gain or lose electrons to form ions.
- Gaining electrons creates a negative ion (more electrons than protons).
- Losing electrons creates a positive ion (more protons than electrons).
- The charge of an ion depends on the difference between the number of protons and electrons.
Elements and the Periodic Table
- Each element is a type of atom defined by its number of protons.
- The periodic table displays elements, each with a unique symbol, atomic number, and mass number.
- The atomic number (bottom left) shows how many protons (and thus electrons in a neutral atom) are in the atom.
- The mass number (top left) equals the total number of protons plus neutrons.
- The number of neutrons = mass number − atomic number.
Key Terms & Definitions
- Atom — Smallest unit of matter, made of a nucleus and electrons.
- Nucleus — Central part of an atom containing protons and neutrons.
- Proton — Positively charged particle in the nucleus; mass = 1.
- Neutron — Neutral particle in the nucleus; mass = 1.
- Electron — Negatively charged particle orbiting the nucleus; very small mass.
- Ion — Atom with a net electric charge due to loss or gain of electrons.
- Element — Substance made of only one type of atom, defined by number of protons.
- Atomic Number — Number of protons in an atom.
- Mass Number — Total number of protons and neutrons in an atom.
Action Items / Next Steps
- Review the periodic table and practice identifying elements using atomic and mass numbers.
- Prepare for next lesson on the types of elements.