Particles in the Atom Electrons (-) charge no mass located outside the nucleus Protons (+) charge 1 amu located inside the nucleus Neutrons no charge 1 amu located inside the nucleus Atom – the smallest unit of an element that retains its chemical properties. Atoms can be split into smaller parts.

Lame Jokes Two atoms are walking down the street. One atom says to the other, “Hey! I think I lost an electron!” The other says, “Are you sure??” “Yes, I’m positive!” A neutron walks into a restaurant and orders a couple of drinks. As she is about to leave, she asks the waiter how much she owes. The waiter replies, “For you, No Charge!!!”

Subatomic particles Actual e- -1 p+ +1 no mass (g) Relative mass Name Symbol Charge Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron no 1 1.67 x 10-24

Structure of the Atom There are two regions Electron cloud The nucleus With protons and neutrons Positive charge Almost all the mass Electron cloud Most of the volume of an atom The region where the electron can be found

Subatomic Particles equal in a neutral atom Atomic Number NUCLEUS ELECTRONS equal in a neutral atom PROTONS NEUTRONS Negative Charge QUARKS Atomic Number equals the # of... Positive Charge Neutral Charge Most of the atom’s mass. Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Counting the Pieces C Atomic Number = number of protons 12 6 C 14 6 C Mass Number = A Atomic Number = number of protons # of protons determines kind of atom Atomic Number = number of electrons in a neutral atom Mass Number = the number of protons + neutrons C 12 6 Atomic Number = Z California WEB

Isotopes: different varieties of an element’s atoms -- have diff. #’s of n0; thus, diff. masses -- some are radioactive; others aren’t All atoms of an element react the same, chemically. Isotope Mass p+ n0 Common Name H–1 1 1 protium H–2 2 1 1 deuterium H–3 3 1 2 tritium C–12 atoms C–14 atoms 6 p+ 6 n0 6 p+ 8 n0 stable radioactive