CHEM 1070 Lecture Notes - Lecture 4: Carbon-12, Periodic Trends, Valence Electron

• School: University of Iowa
• Department: Chemistry
• Course: CHEM 1070
• Professor: Alexeeva Natalia

Document Summary

Atomic mass unit (1/12 of the mass of a carbon-12 atom) serves to quickly count an. In amu, proton is ~1, neutron is ~1, and electron is 0. In these units, a count of an atom"s mass is called the mass number a of an atom. Number of protons in the nucleus identifies an atom as a particular element. Atomic number z of an element is the number of protons in the nucleus. Chemical symbol is the abbreviation unique to each element. Atomic number and chemical symbol both identify the same element. Mass number a the mass of an atom in amu (numerically equal to the sum of the number of protons and neutrons in the nucleus) All atoms of a given element have the same # of protons in the nucleus atomic. F. soddy (1909) discovered that atoms of the same element can have different atomic masses.