Atomic Structure notes page 111

Average mass of atoms of element # of protons in nucleus and the # of electrons in a neutral atom Average mass of atoms of element

Charge/Masses of Atomic Parts: Protons Neutrons Electrons positive charge (+) mass of 1 amu represented by atomic number no/neutral charge (o) negative charge (-) mass is negligible (too small too care) Represented by atomic number IF the atom is neutral (no charge)

To find the # of neutrons in an atom, subtract the atomic number from the atomic mass. (you can round!) 39 - 19 = 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.

Energy Level # of Electrons Held (max.) 1st 2 2nd 8 3rd 18 *Each lower energy level must be filled before a new one can be created.

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”

What makes noble gases so “noble?”

Practice electron configurations of elements