Chemical EquationsChemical Equations

Formulae, names, equations, Formulae, names, equations, moles and stoichiometry moles and stoichiometry

Learning objectivesLearning objectives

Write chemical formulae for substancesWrite chemical formulae for substances Write names for simple compoundsWrite names for simple compounds Apply conservation of matter to balance simple Apply conservation of matter to balance simple

chemical equationschemical equations Define the “mole”Define the “mole” Calculate molar mass of compoundsCalculate molar mass of compounds Apply the mole concept to chemical reactionsApply the mole concept to chemical reactions Describe concentration using molarity, percent Describe concentration using molarity, percent

and ppmand ppm

Most substances are compoundsMost substances are compounds

Two or more elements combinedTwo or more elements combined Constant Composition:Constant Composition:

Compound always contains same amount of Compound always contains same amount of each elementeach element

Chemical formula tells us the number of Chemical formula tells us the number of atoms of each elementatoms of each element Water is HWater is H22OO

Chemical formula: the use of Chemical formula: the use of subscriptssubscripts

Ionic compound:Ionic compound: Formula tells us ratio of the elementsFormula tells us ratio of the elements

• NaCl (Na:Cl = 1:1)NaCl (Na:Cl = 1:1)

• CaClCaCl22 (Ca:Cl = 1: (Ca:Cl = 1:22))

Covalent compound:Covalent compound: Formula tells us number of atoms in moleculeFormula tells us number of atoms in molecule

• CC1212HH2222OO1111 – – 1212 C atoms, C atoms, 2222 H atoms, H atoms, 1111 O atoms O atoms

Formulae and counting atomsFormulae and counting atoms

Ionic and covalentIonic and covalent

IonicIonic (sodium chloride) contain ions (sodium chloride) contain ions Charged particlesCharged particles Electron transferElectron transfer Solutions conduct electricity (electrolytes)Solutions conduct electricity (electrolytes)

CovalentCovalent (sugar) contain molecules (sugar) contain molecules No charged particlesNo charged particles Atoms share electronsAtoms share electrons Solutions don’t conduct electricitySolutions don’t conduct electricity

Covalent molecules and molecular Covalent molecules and molecular formulaformula

Molecular formulaMolecular formula gives number of atoms in gives number of atoms in moleculemolecule Benzene is CBenzene is C66HH66

Simplest formula would be CHSimplest formula would be CH But so is acetylene CBut so is acetylene C22HH22

Molecules can contain thousands of atoms – Molecules can contain thousands of atoms – each one plays a roleeach one plays a role

Naming ionic simple compoundsNaming ionic simple compounds

Simple ionic compounds contain positive Simple ionic compounds contain positive metal ion (metal ion (catcation) and negative nonmetal ion ion) and negative nonmetal ion ((ananion)ion) Metal goes first, name unchangedMetal goes first, name unchanged Nonmetal second, name ending Nonmetal second, name ending → → ideide Subscripts are not namedSubscripts are not named

• Sodium and chlorine Sodium and chlorine → sodium chloride NaCl→ sodium chloride NaCl

• Potassium and oxygen → potassium oxide KPotassium and oxygen → potassium oxide K22OO

• Calcium and fluorine → calcium fluoride CaFCalcium and fluorine → calcium fluoride CaF22

Anions and polyatomic ionsAnions and polyatomic ions

Naming covalent compoundsNaming covalent compounds

There are no metals: There are no metals: what’s the order?what’s the order? More “metallic” one firstMore “metallic” one first Less “metallic” one second, Less “metallic” one second,

end end → → ideide Subscripts are stated Subscripts are stated

(except if first one is one)(except if first one is one)• COCO22 Carbon Carbon didioxideoxide

• NN22O O DiDinitrogen nitrogen monmonoxideoxide

• PP22OO55 DiDiphosphorous phosphorous

pentpentoxideoxide

Counting particles: The MoleCounting particles: The Mole

The mole is a unit of quantity used in The mole is a unit of quantity used in chemistry to measure the number of atoms chemistry to measure the number of atoms or moleculesor molecules

DEFINITION:DEFINITION: The number of atoms in exactly 12 g of The number of atoms in exactly 12 g of 1212CC

A mole of anything always has the same A mole of anything always has the same number of particles: atoms, molecules or number of particles: atoms, molecules or potatoes – 6.02 x 10potatoes – 6.02 x 1023 23 – Avogadro’s number– Avogadro’s number

Atomic and molecular massesAtomic and molecular masses

Two scales:Two scales: Atomic mass unit scaleAtomic mass unit scale

The mass of an individual atom or molecule in The mass of an individual atom or molecule in atomic mass units (amu)atomic mass units (amu)

Molar mass scaleMolar mass scale The mass of a mole of atoms or molecules in The mass of a mole of atoms or molecules in

gramsgrams

Confusing?Confusing?

The Good NewsThe Good News

The mass of a single atom in amu has the The mass of a single atom in amu has the same same numerical value numerical value as its molar mass in gramsas its molar mass in grams The atomic mass of carbon is 12 amuThe atomic mass of carbon is 12 amu The molar mass of carbon is 12 gThe molar mass of carbon is 12 g

The same is true for molecules and compoundsThe same is true for molecules and compounds The formula mass of HThe formula mass of H22O is 18 amuO is 18 amu

The molar mass of HThe molar mass of H22O is 18 gO is 18 g

ExamplesExamples

How many moles are in 13.88 g of lithium if How many moles are in 13.88 g of lithium if the atomic mass of Li is 6.94 amu?the atomic mass of Li is 6.94 amu?

2.002.00

What is the molar mass of CHWhat is the molar mass of CH44 if the atomic if the atomic

mass of H = 1 amu and C = 12 amumass of H = 1 amu and C = 12 amu 16 g16 g

Some molar mass examplesSome molar mass examples