BELLRINGER1. 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?

COUNTING ATOMS

CHEMICAL FORMULAS

• Tell what elements make up the compound and the number of atoms of each element.

RULES FOR COUNTING ATOMS

1. SUBSCRIPTS only refer to the atom that they are BEHIND. For example…

H2SThere are TWO atoms of HYDROGEN and only ONE atom of SULFUR.

COEFFICIENTS

2. COEFFICIENTS apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS.

2 H2S

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!

Polyatomic ions

• A group of atoms that act as a single atom.

• Put in parentheses

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

LET’S PRACTICE!LET’S PRACTICE!

MgCl2

Atoms of Magnesium:

Atoms of Chlorine:

1

2

Al2S3

Atoms of Aluminum:

Atoms of Sulfur:

23

PRACTICEPRACTICE

H2SO4

Atoms of Hydrogen:Atoms of Sulfur:Atoms of Oxygen:

21

CH3OH

Atoms of Carbon:

Atoms of Hydrogen:

Atoms of Oxygen:

14

4

1

THIS COULD BE A LITTLE THIS COULD BE A LITTLE TRICKY…TRICKY…

Ca3(PO4)2 Atoms of Calcium:Atoms of Phosphorus:Atoms of Oxygen:

32

Al2(SO4)3

Atoms of Aluminum:

Atoms of Sulfur:

Atoms of Oxygen:

23

8

12

What about this BAD BOY???What about this BAD BOY???

2Ca3(PO4)2 Atoms of Calcium:Atoms of Phosphorus:Atoms of Oxygen:

64

16

COUNTING ATOMS PRACTICE

Name Use Formula Atoms in Formula

Ex: Calcium Carbonate Limestone CaCO3 Ca= calcium- 1C= carbon- 1O= oxygen – 3

1. Aspirin Pain reliever C9H8O4

2. Paradichlorobenzene Moth Crystals C6H4Cl2

3. Acetic Acid Vinegar C2H4O2

4. TNT

AKA TrinitrotolueneExplosive C7H5(NO2)3

5. Calcium dihydrogen phosphate

Fertilizer Ca(H2PO4)2

6. Pyrite Fool’s Gold FeS2

7. Magnesium hydroxide In Milk of Magnesia

Mg(OH)2

8. Sodium perborate Solid Bleach NaBO3

9. Sucrose Sugar C12H22O11

10. Isopropyl Alcohol Rubbing Alcohol (CH3)2CHOH