COUNTING ATOMS RULES FOR COUNTING ATOMS 1 SUBSCRIPTS

COUNTING ATOMS

RULES FOR COUNTING ATOMS 1. SUBSCRIPTS (baby numbers)= (# of atoms) only refer to the element that they are BEHIND. For example… H 2 S There are TWO atoms of HYDROGEN and only ONE atom of SULFUR. **No number = 1**

“We Do” 1. Ca 2 O • Element: _______ # of Atoms: ______ 2. Hg. CO 3 • Element: _______ # of Atoms: ______

“You Do” 1. Pb. SO 3 • Element: _______ # of Atoms: ______ 2. NH 4 OH • Element: _______ # of Atoms: ______

COEFFICIENTS 2. COEFFICIENTS (BIG # in front) apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS. 2 H 2 S ATOMS OF HYDROGEN: 2 x 2 = 4 ATOMS OF SULFUR: 1 x 2 = 2 IF THERE ISN’T A SUBSCRIPT BEHIND AN ELEMENT, ASSUME THERE IS ONLY ONE ATOM OF THAT ELEMENT!

“We Do” 1. 4 Ca 2 O • Element: _______ # of Atoms: ______ 2. 2 Hg. CO 3 • Element: _______ # of Atoms: ______

“You Do” 1. 3 Pb. SO 3 • Element: _______ # of Atoms: ______ 2. 4 NH 4 OH • Element: _______ # of Atoms: ______

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

“We Do” Ca 3(PO 4)2 • Element: _______ # of Atoms: ______ “You Do” • • • Al 2(SO 4)3 Element: _______ # of Atoms: ______

What about this BAD BOY? ? ? 2 Ca 3(PO 4)2