 negatively charged particles with a mass of a.m.u. (or just put zero) that equal the # of positive protons in the nucleus  their exact location around the nucleus is not known--Heisenberg’s uncertainty principle.  an electrons’s position, momentum, or energy can never be precisely determined  measuring any variable disturbs the others in an unpredictable way

 therefore, we say they are found in an electron cloud or orbital  electron orbitals represent a volume of space where an electron would have a 95% probability of being found  many orbitals can make up an electron level  as electrons are added to an atom, they settle into the lowest unfilled energy leve l

 for this class (Physical Science), each level or orbit, can only hold a certain amount of electrons  1 st → up to 2 electrons  2 nd → up to 8 electrons  3 rd → up to 8 electrons  4 th → up to 8 electrons  (really 18)

 the properties of elements depends on how many electrons are in a particular atom’s different levels  valence electrons are the electrons in the very last or outermost energy level

 draw a sodium atom  and a chlorine atom

 Draw a aluminum atom

 valence electrons are represented as dots around the chemical symbol for the element Na Cl

 Draw the following atoms (Mr. J uses the light table and draws with students)