Download I. Two Kinds of Compound Molecular

[Simulation of Rutherford's expt: http://phet.colorado.edu/simulations/sims.php?sim=Rutherford_Scattering ]
I. Two Kinds of Compound
Molecular- composed of molecules
Ionic- composed of (two kinds of) ions (cations and anions)
II. Ions: The 3rd Kind of Nanoscopic Entity
A. From Before
Atom: Neutral nanoscopic entity with one nucleus (spherical “thing”)
Molecule: Group of atoms somehow “linked” together in some manner (also neutral)
Now add
Ion: Nanoscopic entity (derived from an atom or molecule) having an overall charge. (i.e.,
NOT neutral, which means the total # of e-‘s ≠  total # of p’s
B. Two kinds of ion with respect to sign of charge.
Cation (KAT-ion): ion having a positive charge (e.g., Na+, Mg2+, Fe3+, NH4+)
Anion (ANN-ion): ion having a negative charge (e.g., Cl-, N3-, O2-, OH-, NO3-, PO43-, CN-)
C. Two kinds of ion with respect to “makeup”
Monatomic: [Can be thought of as being] derived from a single atom (with electrons either
added or removed)
Like an “atom with a charge” (except can’t be an atom because atoms are neutral!)
Polyatomic: [Can be thought of as being] derived from a single molecule (with electrons
either added or removed)
Like a “molecule with a charge” (except can’t be a molecule because molecules are
neutral!)
* The atoms in a polyatomic ion are held together the same way that atoms are held
together in a molecule, but 1 or more electrons have been added or removed from
the entire group of atoms.
D. Examples
• Cl atom (add e-) → Cl- ion (monatomic anion) [Pictures and comments not shown here]
• Mg atom (remove 2 e-‘s) → Mg2+ (monatomic cation)
• SO3 molecule (add 2 e-‘s) → SO3 2- (polyatomic anion) [the 2- refers to the WHOLE
GROUP; it is NOT associated with (just) the O!]
N.B. Ions are not “substances” since substances must be “isolatable” (as a solid or liquid, for
example) and thus neutral. Therefore ions are not compounds, even if they have more than
one kind of atom in each ion. Ions can be called a chemical “species”.
An ION ≠ an IONIC COMPOUND! Ionic compounds are MADE OF (2 types of) ions.
III. Chemical Formula (**All substances (and ions) have a chemical formula; mixtures do NOT**)
A. Indicates type of substance: 1 element symbol => element; >1 => compound
B. If a compound, indicates type of compound (with some insight; e.g., M+NM => ionic)
C. Subscripts:
(The numbers that appear to the right and below an element or ion symbol)
• in a compound: Subscripts ALWAYS tell the ratio of atoms/ions in a substance; but
IF the compound is molecular, then the subscripts ALSO indicate the exact number of
each type of atom in one molecule of the compound.
• in an element: if a subscript is present, then the basic units are molecules, not atoms,
and the subscript indicates the exact number of atoms in one molecule of the element.
Examples: P4 (molecular element; each molecule contains 4 P atoms); P4O10 (molecular compound; each
molecule contains 4 P atoms and 10 O atoms); Ca3(PO4)2 (ionic compound; 3 Ca2+ ions are present for
every 2 PO43- ions in the substance; THERE ARE NO MOLECULES IN THIS SUBSTANCE!!)
CO32- (polyatomic ion; each ion is made up of 1 C atom and 3 O atoms joined together [as in a
molecule], but the grouping of 4 atoms overall has a -2 charge [i.e., in TOTAL there are 2 more
e-‘s than protons in the species]