3. How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca Notice that the OH is a group The 2 refers to both H and O How many of each atom are in the following? a) NaOH b) Ca(OH) 2 c) 3Ca(OH) 2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

4. Balancing equations: MgO The law of conservation of mass states that matter can neither be created or destroyed Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction Thus, the number of a particular atom is the same on both sides of a chemical equation Example: Magnesium + Oxygen Mg + O 2  MgO O MgO +  O However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1

5. a)P 4 + O 2  P 4 O 10 b)Li + H 2 O  H 2 + LiOH c)Bi(NO 3 ) 3 + K 2 S  Bi 2 S 3 + KNO 3 d)C 2 H 6 + O 2  CO 2 + H 2 O Balance equations by “inspection” Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. 5 46 72 222 263 From Mg + O 2  MgO 2Mg + O 2  2MgO is correct Mg + ½O 2  MgO is incorrect Mg 2 + O 2  2MgO is incorrect 4Mg + 2O 2  4MgO is incorrect

6. 1.__ KNO 3  __ KNO 2 + __ O 2 2.__ Pb(NO 3 ) 2  __ PbO + __ NO 2 + __ O 2 3.__ P 4 + __ I 2  __ PI 3 4.__ MgO + __ H 3 PO 4  __ Mg 3 (PO 4 ) 2 + __ H 2 O 5.__ Br 2 + __ KI  __ I 2 + __ KBr 6.__ Ca(OH) 2 + __ HNO 3  __ Ca(NO 3 ) 2 + __ H 2 O 7.__ Bi 2 O 3 + __ H 2  __ Bi + __ H 2 O 8.__ Fe + __ O 2  __ Fe 3 O 4 9.__ CaO + __ C  __ CaC 2 + __ CO 2 Balance the Following Equations