CHEM 101 Lecture Notes - Lecture 2: Subatomic Particle, Valence Electron, Atomic Mass

• School: UIC
• Department: Chemistry
• Course: CHEM 101
• Professor: Hatfield Rita

Document Summary

Democritus (470 b. c. ) thought all forms of matter were composed of tiny indivisible particles called atoms derived from the greek word indivisible. Atom- smallest particle of an element that can exist( contains protons, neutrons, electrons) The number written above the symbol of an element on the periodic table. The number is what identifies the element (a. k. a the identity number). The number also represents the number of protons in one atom of the element. There are no two elements with the same number of protons. The sum of the number of protons and neutrons contained in the nucleus of an atom of an element. The mass of electrons is not included because the relative mass of an electron is 0. A x position a is the mass # of the element, position x is the atomic symbol and z is the atomic # Represents the average mass of the isotopes of the element.