Ionic Compounds

What is a compound? A pure substance made of 2 or more elements in defined proportion For example: H2O is always 2 hydrogens and 1 oxygen NaCl is always 1 sodium and 1 chlorine

2 Types of Compounds Ionic Covalent Involves ionic bonding 2 elements trade electrons to become ions Covalent Involves covalent bonding 2 elements share electrons

Anatomy of Ionic Compounds Every ionic compound is made of an anion and a cation. The attraction between positive and negative ions is called ELECTROSTATIC FORCE. This force creates IONIC BONDS.

Structure of Ionic Compounds Anions & cations stack together in a 3-d pattern called a crystal lattice. The lattice is held together by electrostatic forces. The pattern created by the ions is designed to balance charge.

More on Anions & Cations Lost electrons and have a positive charge. Usually metals (less than 4 valence electrons). Anions: Gained electrons and have a negative charge. Usually nonmetals (more than 4 valence electrons). Can be a polyatomic ion.

Ionic Formulas Fact: Charges NEED to be balanced. Atoms: Protons = Electrons Ionic Compounds: + Charge = - Charge Goal: Total positive charge = total negative charge = Zero This is called balancing the formula.

How to Balance A Formula Add the charge of the cation and anion. If the sum is zero, the formula is already balanced so write the cation first then the anion. HINT: Positive before negative!!!

Example Na+1 and Cl-1 (+1) + (-1) = 0 Already Balanced!!! NaCl is the formula

How to Balance A Formula Add the charge of the cation and anion. If the sum is not zero, add cations or anions to make the sum zero. This is a trial and error process. When balanced, write the cation first, then the anion. Use subscripts to indicate how many of each ion are needed.

Example Na+1 and P-3 (+1) + (-3) = -2 Not Balanced!!! Add 2 more Na+1 Na+1, Na+1, Na+1 and P-3 Check: (+1) + (+1) + (+1) + (-3) = 0 Na3P is the formula

Monoatomic Ions All the ions you have seen so far are monoatomic Monatomic = made of 1 atom Na+, Br-1, Al+3 and so on….

Polyatomic Ions Polyatomic = made of more than 1 atom These are special ions. Made of atoms COVALENTLY bonded together that as a group have an overall charge SO4-2, PO4-3 (these are on the back of your periodic table)

What to do with Polyatomic Ions Treat Polyatomic Ions like a normal ion, as one unit. Rules: If more than one polyatomic ion is needed put parentheses around it & subscript outside NEVER change a polyatomic ion formula Example: Mg+2 + OH-1 I need twp OH- ions to balance out the Mg+2 ion. I write the compound as Mg(OH)2, not MgOH2 or MgO2H2