Overview
This lecture explains atomic structure, nuclear symbols, the concept of isotopes, and how to calculate the relative atomic mass using isotope abundances.
Atomic Structure and Elements
- An atom consists of a central nucleus (protons and neutrons) and electrons orbiting the nucleus.
- The number of protons in the nucleus determines which element it is.
- Hydrogen has one proton, helium has two protons and two neutrons.
- The periodic table organizes all ~100 elements, each with its own box and nuclear symbol.
- The atomic number (bottom left of each box) shows the number of protons and is unique to each element.
- Atoms with the same number of protons are the same element.
Nuclear Symbols and the Periodic Table
- Nuclear symbols use one or two letters to represent the element (e.g., C for carbon, Li for lithium).
- Some symbols are based on Latin names, e.g., Na for sodium and Fe for iron.
- The periodic table includes both the symbol and the element name for reference.
Isotopes
- Isotopes are different forms of the same element with the same number of protons but different numbers of neutrons.
- Example: Carbon-12 has six protons, six neutrons; Carbon-13 has six protons, seven neutrons.
- Isotopes react chemically in the same way but have different masses.
Relative Atomic Mass
- The relative atomic mass is the average mass of all isotopes of an element, weighted by their abundances.
- Abundance refers to the percentage of each isotope found in nature.
- To calculate:
- Multiply each isotope's mass by its abundance.
- Add the results.
- Divide by the total abundance.
- Example for copper:
- Copper-63: 69.2% abundance, mass 63.
- Copper-65: 30.8% abundance, mass 65.
- Calculation: (69.2 × 63 + 30.8 × 65) ÷ 100 = 63.6 (to one decimal place).
- The symbol for relative atomic mass is Ar.
Key Terms & Definitions
- Atom — the basic unit of matter with a nucleus (protons, neutrons) and electrons.
- Atomic Number — the number of protons in an atom, unique for each element.
- Isotope — atoms of the same element with different numbers of neutrons.
- Abundance — the percentage of a particular isotope present in nature.
- Relative Atomic Mass (Ar) — the weighted average mass of an element’s isotopes.
Action Items / Next Steps
- Practice calculating relative atomic mass using provided isotope data.
- Review the periodic table to memorize common element symbols and atomic numbers.