Atom, Molecules and Elements
Ions: an atom or group of atoms that has an electric charge.
Isotopes: an atom with different numbers of neutrons in their nucleus. (These extra neutrons have NO EFFECT ON THE CHEMICAL PROPERTIES of the atoms but they do affect the weight of the atom.)
Particle Location Weight Charge
Proton Nucleus 1 amu Positive
Neutron Nucleus 1 amu Neutral
Electrons Electron Cloud 0 amu Negative

Valence electrons: electrons in the outermost shell of an atom.
Atomic Weight: the ratio of the average mass of atoms of an element (average weight of all the isotopes) (# of protons + # of electrons)
Atomic Mass: the mass of a specific isotope
Atomic number: the number of protons found in the nucleus of an atom
Periods: In the periodic table, each horizontal row is called a period. The elements in each period have the same number of shells.
Groups: Each vertical column is called a group. Each of the elements in the same group has the same number of valence electrons in their outer shells.
Covalent Bond: atoms share the electrons.
Ionic Bond: one atom wants to give away an extra electron(s) that it doesn’t need, and one atom wants more electrons to have a complete shell. The atom that gives away an electron becomes positive (*at first it was neutral, but since it gave an electron, which is negative, away, it became positive.), and the one that gains an electron becomes negative. They are held together like magnets (static-magnetic force).
Important info:
Number of Protons = Atomic Number
Number of Electrons = Number of Protons = Atomic Number
Number of Neutrons = Mass Number - Atomic