11/22/09

Hey guys, sorry it took so long to get the blog up.

CH 7.
Significance of a Chemical Formula.

• a chemical formula indicates the relative numbers of each kind of atoms in a chemical compound.
• for a molecular compound, the chemical formula reveals the number of each element conrained in a single molecule of a compound.
• ex. octane - C8H18 (subscripts after element symbols express number of each atom in the molecule.
• the chemical formula for an ionic compound represents one formula unit - the simplest ratio of the compounds positive ions (cations) and its negative ions (anions.)
• ex. Al2(SO4)3
• ( ) around the polyatomic ion identifies it as the unit.
• note. no subscript = UNDERSTOOD TO BE 1.
• Monatomic Ions
• many main-group elements can gain or lose e- to form ions.
• ions formed from a single atom are known as monatomic ions.
• some main-group elements tend to form covalent bonds eather than form ions.
• Naming Monatomic Ions
• monatomic cations are identified simply by elements' name.
• ex. K+ is called potassium cation.
• Mg 2+ is called magnesium cation.
• for monatomic anions, ending of elements' name is dropped, and the ending "-ide" is added to the root name.
• ex. F- is called FLOURIDE anion.
• N3- is called the NITRIDE anion.
• STUDY THE CHAPTER 7 CHARTS GUYS.
• Binary Ionic Compounds
• compunds composed of 2 elements are known as binary compounds.
• in a binary ionic compound, the total number of positive charges and negative charges must be equal.
• the formula for a binary ionic compound can be written given the identities of the compound's ion.
• ex. magnesium bromide
• ions: Mg2+, Br-, Br-
• = MgBr2
• Al3+O2-
• Al2O3
• "CROSS OVER METHOD" = bleh.
• Naming Binary Ionic Compounds
• the nomenclature, or naming system, of binary ionic compounds involves combining the names of the compound's positive and negative ions.
• the name of the cation is given 1st; followed by name of the anion.
• ex. Al2O3 - aluminum oxide.