Atomic Structure notes page 107 # of protons in nucleus and the # of electrons in a neutral atom Average mass of atoms of element Protons Neutrons Electrons positive charge (+) mass of 1 amu represented by atomic number no/neutral charge (o) mass of 1 amu negative charge (-) mass is negligible (too small too care) Represented by atomic number IF the atom is neutral (no charge) Charge/Masses of Atomic Parts: To find the # of neutrons in an atom, subtract the atomic number from the atomic mass. (you can round!) = 20 So why does the atomic mass have a decimal? Isotope Variation of an element due to change in the # of neutrons all atoms of a particular element with have the same # of protons, but the # of neutrons can vary. ex.) Carbon-12, Carbon-13, and Carbon-14 are all isotopes of the element Carbon each has only 6 protons, but 6, 7, and 8 neutrons, respectively. Electrons usually equal to # of protons, so charges cancel and the atom is neutral. sort themselves into energy levels- only a certain number of electrons can fit on each energy level. *Each lower energy level must be filled before a new one can be created. Energy Level # of Electrons Held (max.) 1st2 2nd8 3rd18 Energy Levels and Electron Configuration Lower energy levels must be filled before a new level is created. electrons in outermost energy level are called Valence Electrons Energy levels dont like to be partially full- their goal is to gain or lose electrons to become full. What makes noble gases so noble? Practice electron configurations of elements