Overview
This lecture introduces subatomic particles—protons, neutrons, and electrons—and explains how to interpret entries in the periodic table, with a focus on atomic structure.
Subatomic Particles
- Subatomic means smaller than an atom; these are particles inside atoms.
- The three key subatomic particles are protons, neutrons, and electrons.
- Atoms are made of protons and electrons; most also have neutrons, but not all.
- The number of each subatomic particle varies between different atoms.
The Periodic Table
- The periodic table organizes elements by the number of subatomic particles.
- Each element’s entry shows unique properties based on these particles.
- Elements are arranged left to right by increasing atomic number and weight.
- Columns group elements with similar properties.
Reading a Periodic Table Entry (Example: Sodium)
- The top number is the atomic number (ID number)—for sodium, it is 11.
- The middle symbol (Na) is the atomic symbol; typically one or two letters.
- The lower number is the atomic mass number (for sodium, 22.990).
- Atomic number identifies the element and the number of protons in the atom.
Structure of an Atom
- Most of an atom is empty space; the nucleus is tiny in comparison.
- The nucleus is the central part and contains protons and neutrons.
- Electrons are found outside the nucleus, moving within defined regions.
- Protons and neutrons are tightly packed in the nucleus, while electrons occupy the surrounding space.
Key Terms & Definitions
- Subatomic particle — a particle smaller than an atom (proton, neutron, electron).
- Proton — positively charged particle in the nucleus.
- Neutron — neutral particle in the nucleus.
- Electron — negatively charged particle found outside the nucleus.
- Nucleus — the center of the atom containing protons and neutrons.
- Atomic number — the number of protons in an atom, unique to each element.
- Atomic mass number — the average mass of an atom, typically shown below the atomic symbol.
Action Items / Next Steps
- Review the periodic table in your textbook or assignment.
- Practice identifying atomic number, symbol, and mass number for various elements.