CHEM-UA 125 Chapter 2.3: Chapter 2 part 3
Document Summary
Atomic number, mass number, and atomic symbol: the atomic number z of an element equals the number of protons in the nucleus of each of its atoms. The isotopic composition of an element is determined by mass spectrometry, a method for measuring the relative masses and abundances of atomic-scale particles very precisely (mass of silicon 28 atom)/( mass of carbon 12 standard) = 2. 331411. Isotopic mass of silicon-28 = measured mass ratio x mass of carbon-12. Mass spectrometer gives the relative abundance as a percentage of each isotope in a sample of the element. The atomic mass/ weight- the average of the masses of its naturally occurring isotopes weighted according to their abundances. The atomic mass is an average value: the atomic-mass interval. The atomic-mass interval is used for 10 elements: hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, and thallium. The mass is greater than or equal to 1. 00784 and less than or equal to.