Chemical Formulas and Equations

Getting started with some definitions…

ATOM ATOM - is the smallest whole part of an element ELEMENT ELEMENT - matter made of only one kind of atom MOLECULE - two or more elements that have chemically combined Each new element is identified by a capital letter Each new element is identified by a capital letter Example: H 2 SO 4 Example: H 2 SO 4 There are three ELEMENTS in sulfuric acid There are three ELEMENTS in sulfuric acid Hydrogen Hydrogen Sulfur Sulfur Oxygen Oxygen CHEMICAL FORMULA - contains chemical symbols and subscripts to show the number and types of atoms in a compound

SUBSCRIPT – after a chemical symbol and shows the number of each ATOM in a chemical formula formula Example: C 12 H 22 O 11 Example: C 12 H 22 O atoms of Carbon 12 atoms of Carbon 22 atoms of Hydrogen 22 atoms of Hydrogen 11 atoms of Oxygen 11 atoms of Oxygen If there is no subscript, it is understood to be 1 If there is no subscript, it is understood to be 1 Example: NaCl Example: NaCl 1 atom of Sodium 1 atom of Sodium 1 atom of Chlorine 1 atom of Chlorine

You Practice! NaHCO 3 Na = 1 H = 1 C = 1 O = 3 K 2 Cr 2 O 7 K = 2 Cr = 2 O = 7

What about Formulas with Parentheses??? EX: Pb(NO 3 ) 2 EX: Pb(NO 3 ) 2 The “2” after the parenthesis indicates there are two of what’s in the parentheses The “2” after the parenthesis indicates there are two of what’s in the parentheses You could think of it this way: You could think of it this way: (NO 3 ) and (NO 3 ) You MULTIPLY everything INSIDE the parentheses by the subscript at the end: Pb = 1 N = 2 (1 N x 2) O = 6 (3 O x 2) O = 6 (3 O x 2)

You Practice!! (NH 4 ) 3 PO 4 N = 3 (3 x 1 N) H = 12 (3 x 4 H) P = 1 (1 x 1 P) O = 4 (1 x 4 O) Mg(OH) 2 Mg = 1 O = 2 (2 x 1 O) H = 2 (2 x 1 H)

COEFFICIENT - in front of the chemical formula and shows the number of MOLECULES and shows the number of MOLECULES 2 H 2 (SO 4 ) This means there are 2 molecules of H 2 (SO 4 ) This means there are 2 molecules of H 2 (SO 4 ) You could think of it this way – You could think of it this way – H 2 (SO 4 ) and H 2 (SO 4 )

MULTIPLY coefficients by ALL of the subscripts in the chemical formula: MULTIPLY coefficients by ALL of the subscripts in the chemical formula: 2H 2 SO 4 H = 4 (2 x 2 H) S = 2(2 x 1 S) O = 8(2 x 4 O)

You Practice!! 3 Ca 3 (PO 4 ) 2 Ca = 9 (3 x 3 Ca) P = 6 (3 x 1 P x 2) O = 24 (3 x 4 O x 2) 2 H 2 O H = 4 (2 x 2 H) O = 2 (2 x 1 O)

Got It???? Homework Time… Counting Atoms WS

Chemical Equations A CHEMICAL EQUATION shows what happens in a chemical reaction 2 K + Cl 2 2 KCl The + separates molecules on the same side The + separates molecules on the same side ReactantsProducts “yields”

States that mass cannot be created or destroyed States that mass cannot be created or destroyed In other words, the mass of the reactants is equal to the mass of the products In other words, the mass of the reactants is equal to the mass of the products Proved by French chemist Antoine Lavoisier ( ) Proved by French chemist Antoine Lavoisier ( ) known as the “Father of Modern Chemistry” known as the “Father of Modern Chemistry” Lavoisier, 1788 Law of Conservation of Mass

Well, consider the following equation: H2 + O2H2O This cannot happen….an oxygen atom cannot be destroyed!!! Reactants: H = 2 O = 2 Products: H = 2 O = 1 So what does that have to do with anything??

So what do we do? The chemical equation must be written according to the law of conservation of mass according to the law of conservation of mass How it actually happens in nature is like this…. 2 H 2 + O 2 2 H 2 O Coefficents are added to balance on paper… Coefficents are added to balance on paper… Reactants:Products: Reactants:Products: H = 4 H = 4 O = 2 O = 2 O = 2 O = 2 There MUST be the same number AND types of atoms on both sides of the equation!

Are These Equations Balanced? Na + O 2 Na 2 O Na = 1 Na = 2 O = 2 O = 1 Mg + 2 HCl MgCl 2 + H 2 Mg = 1 Mg = 1 H = 2 H = 2 Cl = 2 Cl = 2 NOPE YEP!!

You Practice!!! MgO Mg + O 2 Mg =1Mg = 1 O =1O = 2 N H 2 2 NH 3 N =2N = 2 H =6H = 6 Zn + 2 HClZnCl 2 + H 2 Zn = 1Zn = 1 H =2H = 2 Cl =2Cl = 2 NOPE YEP!!

More Practice K + Br 2 KBr K = 1 K = 1 Br =2 Br = 1 Fe + O 2 6Fe 2 O 3 Fe = 1 Fe = 12 O = 2 O = 18 2Na + 2H 2 O2NaOH + H 2 Na = 2 Na = 2 O = 2 O = 2 H = 4 H = 4 NOPE YEP!!

So What About the Unbalanced Equations???... WE MUST BALANCE THEM!! K + Br 2 KBr K = 1 K = 1 Br =2 Br = 1 Add COEFFICIENTS and recount

More Practice Fe + O 2 6Fe 2 O 3 Fe = 1 Fe = 12 O = 2 O = 18 Add COEFFICIENTS and recount

One More!!! Na + O 2 Na 2 O Na = 1 Na = 2 O = 2 O = 1 Add COEFFICIENTS and recount

Got It??? Your turn… Homework time!! Balanced or Not?