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[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]