e- p+ n0 0 amu 1 amu 1 amu Electron proton Neutron Subatomic Particle Symbol Charge Mass (amu) Where is it found? Negative (-1) Electron Cloud e- 0 amu Electron proton p+ Positive (+1) 1 amu Nucleus n0 1 amu Nucleus Neutral (0) Neutron Atomic mass unit (AMU)- the SI unit used to express the mass of the particles in an atom.
Two regions of an atom: Nucleus Electron cloud 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
More about atoms All elements are different from each other because of the number of p+, e- and n0 they have. 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 - )
How to determine # of e-, n0 & p+: Atomic Number = # of protons (if an atom, then p+ = e-) Find atomic number on periodic table.
H 1 Hydrogen 1.00794 Atomic Number # of Protons Which then tells us: ELEMENT SYMBOL What does the atomic number tell us About a typical atom? 1 H Hydrogen 1.00794 # of Protons Which then tells us: # of electrons AVERAGE ATOMIC MASS
Element # of protons # of Neutrons # of Electrons Atomic Mass Atomic number H He Ar 1 1 1.0079 1 2 2 2 2 4.0026 18 22 18 18 39.95