Chemistry 1027A/B Lecture Notes - Molar Concentration, Stoichiometry, Mass Number

• School: Western University
• Department: Chemistry
• Course: Chemistry 1027A/B
• Professor: Kay Calvin

Document Summary

Atoms are the building blocks: protons, neutrons, and electrons. Protons and neutrons have almost the same mass (each has a mass almost equal to one atomic mass unit [amu]) Electron is only about 1/2000th of the mass of a proton or neutron. All atoms of the same element have the same number of protons in the nucleus. The mass number is the total number of protons and neutrons in an atom. Mass number = number of proton + number of neutrons. Same number of protons but different number of neutrons therefore different mass number. Same atomic number but different mass number. Isotopic abundance is the percent by number of each of the isotopes of an element. The atomic mass standard is based on the mass of c-12. The atomic masses of all other elements in the periodic table have been measured using c-12 mass as exactly 12 u.