Overview
The lecture explains the concept of Relative Atomic Mass in chemistry, using real-life analogies to describe how atomic masses are compared to a standard, specifically the carbon-12 isotope.
Understanding Relative Atomic Mass
- Relative means comparing something with a standard reference.
- In chemistry, atomic mass is compared to a standard mass, not measured absolutely.
- A daily life example: comparing the weight of vegetables using standard weights on a balance.
Standard in Chemistry: Carbon-12
- The standard used in chemistry is the carbon-12 isotope.
- Isotopes are forms of an element with different numbers of neutrons; carbon-12 is the most common.
- Carbon-13 and carbon-14 are less common carbon isotopes; carbon-14 is radioactive.
Definition and Explanation
- The textbook definition: Relative Atomic Mass is based on 1/12th the mass of a carbon-12 atom.
- If an atom of carbon-12 is divided into 12 equal parts, one part is used as the standard reference.
- This 1/12th part is defined as one atomic mass unit (amu).
How Relative Atomic Mass Works
- Relative Atomic Mass allows us to compare the mass of other atoms to this standard unit.
- It is a way to express the mass of atoms without using extremely small numbers.
Key Terms & Definitions
- Relative Atomic Mass — The ratio of the average mass of an atom to 1/12th the mass of a carbon-12 atom.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Carbon-12 — The standard isotope of carbon with 6 protons and 6 neutrons.
- Atomic Mass Unit (amu) — The mass equal to 1/12th of a carbon-12 atom.
Action Items / Next Steps
- Review the definition of Relative Atomic Mass and Atomic Mass Unit in your textbook.
- Be prepared to answer how Relative Atomic Mass is determined using carbon-12 as a standard.