Overview
This lecture explains atomic structure, the organization and interpretation of the periodic table, isotopes, and how to calculate relative atomic mass using isotope abundances.
Atomic Structure
- Atoms consist of a central nucleus (protons and neutrons) surrounded by electrons in orbit.
- The number of protons in the nucleus determines the element.
- Hydrogen has one proton and one electron; helium has two protons, two neutrons, and two electrons.
The Periodic Table and Nuclear Symbols
- The periodic table organizes about 100 elements, each in a box called a nuclear symbol.
- The atomic number (bottom left in the box) shows the number of protons and identifies the element.
- Each element has a unique one- or two-letter symbol (e.g., C for carbon, Li for lithium, Na for sodium, Fe for iron).
Identifying Elements
- An atom's element is defined solely by its number of protons (atomic number).
- To identify an element, match the number of protons to its atomic number on the periodic table.
Isotopes
- Isotopes are forms of the same element with identical numbers of protons but different numbers of neutrons.
- Chemical behavior is nearly identical for all isotopes of an element.
- Example: Carbon-12 has 6 protons and 6 neutrons; carbon-13 has 6 protons and 7 neutrons.
Relative Atomic Mass
- Relative atomic mass is the weighted average mass of all isotopes of an element.
- To calculate: Multiply each isotope's abundance by its mass, sum the results, then divide by total abundance.
- Example for copper: Relative atomic mass = [(69.2 × 63) + (30.8 × 65)] / (69.2 + 30.8) = 63.6 (rounded to 1 decimal place).
- The symbol for relative atomic mass is A_r.
Key Terms & Definitions
- Atom — Smallest unit of an element, with protons, neutrons, and electrons.
- Nucleus — Central part of an atom, containing protons and neutrons.
- Proton — Positively charged particle in the nucleus; defines the element.
- Neutron — Neutral particle in the nucleus.
- Electron — Negatively charged particle orbiting the nucleus.
- Atomic Number — Number of protons in an atom; unique to each element.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Relative Atomic Mass (A_r) — Weighted average mass of all isotopes of an element.
Action Items / Next Steps
- Review periodic table symbols and atomic numbers.
- Practice calculating relative atomic mass from isotope data.
- Learn definitions for key atomic structure terms.