COUNTING ATOMS RULES FOR COUNTING ATOMS 1. SUBSCRIPTS (baby numbers)= (# of atoms) only refer to the element that they are BEHIND. For example… H2S There are TWO atoms of HYDROGEN and only ONE atom of SULFUR.**No number = 1** “We Do” 1. Ca2O • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ 2. HgCO3 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ “You Do” 1. PbSO3 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ 2. NH4OH • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ COEFFICIENTS 2. COEFFICIENTS (BIG # in front) apply to the entire compound. You MULTIPLY the coefficients and SUBSCRIPTS. 2 H2S 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. 4Ca2O • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ 2. 2HgCO3 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ “You Do” 1. 3PbSO3 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ 2. 4NH4OH • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • 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” Ca3(PO4)2 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ “You Do” Al2(SO4)3 • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ • Element: _______ # of Atoms: ______ What about this BAD BOY??? 2Ca3(PO4)2