1. BELLRINGER 1. What is the chemical formula for water? 2. How many hydrogen atoms are in a water molecule? 3. How many oxygen atoms are in a water molecule?

2. COUNTING ATOMS

3. CHEMICAL FORMULAS Tell what elements make up the compound and the number of atoms of each element.

4. RULES FOR COUNTING ATOMS 1.SUBSCRIPTS only refer to the atom that they are BEHIND. For example… H 2 S There are TWO atoms of HYDROGEN and only ONE atom of SULFUR.

5. COEFFICIENTS 2.COEFFICIENTS apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS. 2 H 2 S ATOMS OF HYDROGEN: ATOMS OF SULFUR: 4 2 IF THERE ISN’T A SUBSCRIPT BEHIND AN ELEMENT, ASSUME THERE IS ONLY ONE ATOM OF THAT ELEMENT!

6. Polyatomic ions A group of atoms that act as a single atom. Put in parentheses

7. PARENTHESES 3. If elements or compounds are inside of PARENTHESES, then the SUBSCRIPT behind the parentheses applies to everything inside. Ba(OH) 2 ATOMS OF BARIUM: ATOMS OF OXYGEN: ATOMS OF HYDROGEN: 1 2 2

8. LET’S PRACTICE! MgCl 2 Atoms of Magnesium: Atoms of Chlorine: 1 2 Al 2 S 3 Atoms of Aluminum: Atoms of Sulfur: 2 3

9. PRACTICE H 2 SO 4 Atoms of Hydrogen: Atoms of Sulfur: Atoms of Oxygen: 2 1 CH 3 OH Atoms of Carbon: Atoms of Hydrogen: Atoms of Oxygen: 1 4 4 1

10. THIS COULD BE A LITTLE TRICKY… Ca 3 (PO 4 ) 2 Atoms of Calcium: Atoms of Phosphorus: Atoms of Oxygen: 3 2 Al 2 (SO 4 ) 3 Atoms of Aluminum: Atoms of Sulfur: Atoms of Oxygen: 2 3 8 12

11. What about this BAD BOY??? 2Ca 3 (PO 4 ) 2 Atoms of Calcium: Atoms of Phosphorus: Atoms of Oxygen: 6 4 16

12. COUNTING ATOMS PRACTICE NameUseFormulaAtoms in Formula Ex: Calcium CarbonateLimestoneCaCO 3 Ca= calcium- 1 C= carbon- 1 O= oxygen – 3 1.AspirinPain relieverC9H8O4C9H8O4 2. ParadichlorobenzeneMoth CrystalsC 6 H 4 Cl 2 3. Acetic AcidVinegarC2H4O2C2H4O2 4. TNT AKA Trinitrotoluene ExplosiveC 7 H 5 (NO 2 ) 3 5. Calcium dihydrogen phosphate FertilizerCa(H 2 PO 4 ) 2 6. PyriteFool’s GoldFeS 2 7. Magnesium hydroxide In Milk of Magnesia Mg(OH) 2 8. Sodium perborateSolid BleachNaBO 3 9. SucroseSugarC 12 H 22 O 11 10. Isopropyl AlcoholRubbing Alcohol(CH 3 ) 2 CHOH