Chemical Equations Formulae, names, equations, moles and stoichiometry

Learning objectives  Write chemical formulae for substances  Write names for simple compounds  Apply conservation of matter to balance simple chemical equations  Define the “mole”  Calculate molar mass of compounds  Apply the mole concept to chemical reactions  Describe concentration using molarity, percent and ppm

Most substances are compounds  Two or more elements combined  Constant Composition:  Compound always contains same amount of each element  Chemical formula tells us the number of atoms of each element  Water is H 2 O

Chemical formula: the use of subscripts  Ionic compound:  Formula tells us ratio of the elements NaCl (Na:Cl = 1:1)NaCl (Na:Cl = 1:1) CaCl 2 (Ca:Cl = 1:2)CaCl 2 (Ca:Cl = 1:2)  Covalent compound:  Formula tells us number of atoms in molecule C 12 H 22 O 11 – 12 C atoms, 22 H atoms, 11 O atomsC 12 H 22 O 11 – 12 C atoms, 22 H atoms, 11 O atoms

Formulae and counting atoms

Ionic and covalent  Ionic (sodium chloride) contain ions  Charged particles  Electron transfer  Solutions conduct electricity (electrolytes)  Covalent (sugar) contain molecules  No charged particles  Atoms share electrons  Solutions don’t conduct electricity

Covalent molecules and molecular formula  Molecular formula gives number of atoms in molecule  Benzene is C 6 H 6  Simplest formula would be CH  But so is acetylene C 2 H 2  Molecules can contain thousands of atoms – each one plays a role

Naming ionic simple compounds  Simple ionic compounds contain positive metal ion (cation) and negative nonmetal ion (anion)  Metal goes first, name unchanged  Nonmetal second, name ending → ide  Subscripts are not named Sodium and chlorine → sodium chloride NaClSodium and chlorine → sodium chloride NaCl Potassium and oxygen → potassium oxide K 2 OPotassium and oxygen → potassium oxide K 2 O Calcium and fluorine → calcium fluoride CaF 2Calcium and fluorine → calcium fluoride CaF 2

Anions and polyatomic ions

Naming covalent compounds  There are no metals: what’s the order?  More “metallic” one first  Less “metallic” one second, end → ide  Subscripts are stated (except if first one is one) CO 2 Carbon dioxideCO 2 Carbon dioxide N 2 O Dinitrogen monoxideN 2 O Dinitrogen monoxide P 2 O 5 Diphosphorous pentoxideP 2 O 5 Diphosphorous pentoxide

Counting particles: The Mole  The mole is a unit of quantity used in chemistry to measure the number of atoms or molecules  DEFINITION:  The number of atoms in exactly 12 g of 12 C  A mole of anything always has the same number of particles: atoms, molecules or potatoes – 6.02 x – Avogadro’s number

Atomic and molecular masses  Two scales:  Atomic mass unit scale  The mass of an individual atom or molecule in atomic mass units (amu)  Molar mass scale  The mass of a mole of atoms or molecules in grams  Confusing?

The Good News  The mass of a single atom in amu has the same numerical value as its molar mass in grams  The atomic mass of carbon is 12 amu  The molar mass of carbon is 12 g  The same is true for molecules and compounds  The formula mass of H 2 O is 18 amu  The molar mass of H 2 O is 18 g

Examples  How many moles are in g of lithium if the atomic mass of Li is 6.94 amu?  2.00  What is the molar mass of CH 4 if the atomic mass of H = 1 amu and C = 12 amu  16 g

Some molar mass examples