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Published byHelena Boone Modified over 7 years ago
Introduction to Chemical Compounds Why do elements combine?
So Far We’ve Learned: That atoms are made up of Protons, Neutrons, and Electrons The identity of an atom is determined by the number of protons in the nucleus BUT, compounds form due to the interactions between electrons
How are Electrons Involved? I. Either Shared (Covalent) or Transferred (Ionic) Using the Periodic Table, we can predict an element’s electron behavior. A (-) charge = gained electrons A (+) charge = lost electrons
General Rules (ionic): Metals will ALWAYS form + ions (cations) Non-metals will ALWAYS form – ions (anions) Chemical compounds form from the interaction between oppositely charged ions: Na +1 + Cl -1 -------> NaCl sodium ion + chloride ion ----> sodium chloride
BIG IDEA: Every element is trying to rearrange its electrons (by gaining or losing them) in order to “look like” a noble gas element. This is called achieving a “Noble Gas Configuration. (Full outer electron shell)
Predicting Oxidation Number by Position
Identifying Ions NameCommon Ion (Na +1 )Cation or AnionAnion “ide” name Strontium Iodine Nitrogen Oxygen Lithium Magnesium Silver Zinc Iron (II) Phosphorous Sulfur Aluminum Fluorine Chlorine Potassium Bromine Cesium Francium Chromium (VI)
When Ions Combine, the Compound MUST be Neutral All (+) charges must be cancelled by (-) charges Need to combine ions in smallest proportion that will cancel charges.
Li and Cl Mg and Cl Al and Cl Li and O Mg and O H and S
ANSWERS: LiCl ( Li +1 + Cl -1 ) MgCl 2 (Mg +2 + 2Cl -1 ) AlCl 3 (Al +3 + 3Cl -1 ) Li 2 O (2Li +1 + O -2 ) MgO (Mg +2 + O -2 ) H 2 S (2H +1 + S -2 )
Anatomy of a Chemical Formula 1. Symbols for the elements in the compound 2. Numbers called subscripts that indicate how many atoms of an element are present: AlCl 3 = 1 Al and 3 Cl This should makes sense because Al has a +3 charge and Cl has a -1 charge 3. The subscript is ONLY associated with the element symbol to the immediate left.
TRY THESE: Roman numerals indicate value of positive charge
Polyatomic Ions “Poly-” means many Polyatomic ions are charged particles that consist of more than one atom These ions can combine just like ions formed from single elements
Common Polyatomic Ions
Just One Catch! If more than one polyatomic ion is needed, the formula for the compound will need to have parenthesis around this ion Example: Mg +2 + PO 4 -3 ----> Mg 3 (PO 4 ) 2
Polyatomic Ions May be Used Like Other Ions Just like Sodium (Na + ) can combine with chloride (Cl -1 ), to make NaCl A polyatomic ion called ammonium (NH 4 +1 ) can combine with chloride (Cl -1 ) to make NH 4 Cl The N and 4 H’s that make up NH 4, collectively loose 1 electron to become NH 4 +1
Ion Cut-Out Lab
Goal: Make Compounds Using Paper Models of Ions KBr Postassium Bromide K 3 PO 4 Potassium Phosphate Goal for today: Complete as much of chart as possible. Do NOT Name compounds.
Naming Ionic Compounds 1. Determine the ions that make up the compound. (Use Periodic Table or “Common Ions Chart”) 2. Write the name of the POSITIVE ion first 3. Write the name of the NEGATIVE ion second. (Sometimes the name of this ion will change slightly)
Negative Ion Names Name ending changes to “-ide” Non-metal elements in columns 14-17 will form negative ions with names ending in “-ide”.
Examples: Chlorine becomes chloride Fluorine becomes fluoride Oxygen becomes oxide Phosphorous becomes phosphide Nitrogen becomes nitride
If polyatomic ions are used... Naming is easy! Just put the names of the ions together (positive first, negative second) No Name changes are needed Example: Mg 3 (PO 4 ) 2 is named Magnesium phosphate Positive ionNegative ion
Transition Metals If the positive ion is a transition metal, the name of the compound MUST include a Roman Numeral! Here’s an example: There are two “iron chlorides”: FeCl 2 is iron (II) chlorideFeCl 3 is iron (III) chloride The Roman Numeral indicates the charge of the metal ion
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