CHEM 6A Lecture 10: CHEM W2 Lec 10/13/17
3 Jun 2018
School
Department
Course
Professor
Current relative scale of atomic masses
● The mass of one 12C atom is exactly 12 amu, where amu (or u) represents “atomic mass
unit”
● 1 amu = 1 * (mass of one 4C atom)
12
● Mass of one neutron = 1.00867 amu
● Mass of one proton = 1.00728 amu
● In SI units, 1 amu = 1.66054 * 10-27 kg
Isotopes
● Atoms of the same element (same # of protons) with different number of neutrons
(different mass numbers)
● Atomic mass of an element is the weighted average of masses of stable isotopes based
on natural abundances
○ See text p. 66-67 for how those are determined
E.g. atomic mass of silver
Isotopes
Mass (amu)
Abundance (%)
107Ag
106.90509
51.84%
109Ag
108.90476
48.16
Atomic mass of Ag = ( 106.90509 amu )( 56.886) + (108.90476 amu)(48.16)
100 100
= 55.419 amu + 52.44 amu
=107.87 amu
Clicker question:
A
B
X
46.7g
53.3g
a.
30.4g
69.6g
19
CHEM 6A Full Course Notes
Verified Note
19 documents
Document Summary
The mass of one 12c atom is exactly 12 amu, where amu (or u) represents atomic mass unit . 1 amu = 1 * (mass of one 4c atom) Mass of one neutron = 1. 00867 amu. Mass of one proton = 1. 00728 amu. In si units, 1 amu = 1. 66054 * 10-27 kg. Atoms of the same element (same # of protons) with different number of neutrons (different mass numbers) Atomic mass of an element is the weighted average of masses of stable isotopes based on natural abundances. See text p. 66-67 for how those are determined. Atomic mass of ag = ( 106. 90509 amu )( 56. 886) + (108. 90476 amu)(48. 16) Cations(+) and anions(-) bound together by ionic bounds (charge attraction) resulting in a neutral species. Two or more atoms bound together by covalent bonds (sharing of electrons) Organic: contains mostly c and h atoms. Ions: # protons != # electrons, therefore it is charged.
