CHE 2A Lecture Notes - Lecture 2: Unified Atomic Mass Unit, Atomic Mass (Band), Atomic Number

• School: UC-Davis
• Department: Chemistry
• Course: CHE 2A
• Professor: Andreas Toupadakis

Document Summary

Che2a-d05 lecture 2 notes - counting and weighing atoms and molecules. How to count weight" in atoms and molecules. A substance whose atoms all have same atomic number. Atoms of same element but different mass (because different numbers in the nuclei) Desire convenient numbers at the atomic level. If expressed in amu, it is not a convenient number, however g or kg. Need a standard of mass, a reference point. If mass of carbon-12 is: (insert picture of circle) 1/12 of mass of c-12 is 1 amu (pie circle with 1/12 shaded as 1amu = mass) Therefore 1 amu = 1/12 mass of c-12. Mass c-12 = 12 amu by definition. Mass of copper-63 is 62. 9298 amu ( 63 times the amu ) By experiment mass of c-12 atpm = 1. 9927 x 10^-23g. Mass of c12 atom =- (3 lines) (by definition 12 amu) 1. 9927 x 10^-23 g = 12 amu. Atomic mass = mass of one atom .