1. Subatomic Particle SymbolChargeMass (amu) Where is it found? Atomic mass unit (AMU)- the SI unit used to express the mass of the particles in an atom. Electron proton Neutron e-e-e-e- p+p+p+p+ n0n0n0n0 Negative (-1) (-1) Positive (+1) (+1) Neutral (0) (0) 0 amu 1 amu Electron Cloud Nucleus Nucleus

2. Two regions of an atom: Nucleus –Where most of the mass is found –Has protons and neutrons –Central dense region of an atom Electron cloud –Possible region where e - can be found around the nucleus

3. More about atoms All elements are different from each other because of the number of p +, e - and n 0 they have. “electrically neutral”Elements are said to be “electrically neutral”  # of e- = # of p+ If an atom has different numbers of e- and p+ then they are called IONS Ions – atom with a charge (can be + or - )

4. How to determine # of e -, n 0 & p + : Atomic Number = # of protons (if an atom, then p+ = e- = n0) Find atomic number on periodic table.

5. 1 H Hydrogen 1.00794 Atomic Number ELEMENT SYMBOL AVERAGE ATOMIC MASS What does the atomic number tell us About a typical atom? # of Protons Which then tells us: # of electrons

6. Element # of protons # of Neutrons # of Electrons Atomic Mass Atomic number H He Ar 101 1.0079 1 2 22 4.0026 2 39.95 18