Overview
This lecture reviews the basic structure of the atom, the concept of isotopes, electron energy levels, and the process of ionization.
Atomic Structure
- The nucleus, located at the center of an atom, contains protons and neutrons.
- Protons have a positive charge (+1) and neutrons are neutral; both have a relative mass of 1.
- Electrons orbit the nucleus in shells, are negatively charged (-1), and are about 2000 times smaller than protons or neutrons.
- In a neutral atom, the number of protons equals the number of electrons.
The Periodic Table and Nuclear Symbols
- Each element is represented by a box (nuclear symbol) on the periodic table.
- The elemental symbol (e.g., Li for lithium) identifies the element.
- Atomic number (bottom left) shows the number of protons and determines the element's identity.
- Mass number (top left) is the total number of protons and neutrons in the atom.
Isotopes
- Isotopes are atoms of the same element (same number of protons) with different numbers of neutrons.
- Different isotopes have different mass numbers (e.g., lithium-6, lithium-7, lithium-8).
- Most elements have only one or two stable isotopes; unstable isotopes decay by emitting radiation (radioactive decay).
Electron Energy Levels
- Electrons are arranged in shells (energy levels) around the nucleus.
- Electrons usually stay in their shell but can move to a higher shell if they absorb the correct amount of energy (excitation).
- Excited electrons eventually return to lower energy levels, emitting electromagnetic radiation.
Ionization
- If an electron absorbs enough energy, it can leave the atom entirely, creating a positive ion.
- Ionizing radiation is radiation that can remove electrons from atoms, thus ionizing them.
Key Terms & Definitions
- Nucleus — Central part of an atom containing protons and neutrons.
- Proton — Positively charged particle in the nucleus.
- Neutron — Neutral particle in the nucleus.
- Electron — Negatively charged particle orbiting the nucleus.
- Atomic Number — Number of protons in an atom.
- Mass Number — Sum of protons and neutrons in an atom.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Ion — Atom that has lost or gained electrons, giving it a charge.
- Ionizing Radiation — Radiation that can remove electrons from atoms.
Action Items / Next Steps
- Review radioactive decay and its connection to unstable isotopes in the next video.