ChemistryChemistry

Tutorial #4Tutorial #4

Chemical CompoundsChemical Compounds

Elements – pure substance made of one Elements – pure substance made of one type of particletype of particle

Compound – when two or more elements Compound – when two or more elements combinecombine

Elements are held together by chemical Elements are held together by chemical bondsbonds

Chemical bonds form when an element Chemical bonds form when an element gains,loses or shares an electron (charged gains,loses or shares an electron (charged particle)particle)

Chemical FormulasChemical Formulas Use symbols and numbers (subscripts) to Use symbols and numbers (subscripts) to

represent the composition of a pure substancerepresent the composition of a pure substance Symbols for each element are usedSymbols for each element are used Subscript (#’s) represent the number of atoms Subscript (#’s) represent the number of atoms

of each elementof each element

Eg. HEg. H22o – o – H=symbol of hydrogenH=symbol of hydrogen o=symbol for oxygeno=symbol for oxygen

2= 2 atoms of hydrogen2= 2 atoms of hydrogen* note: if a symbol has no subscript it is said to * note: if a symbol has no subscript it is said to

represent having 1 atom.represent having 1 atom.

Molecular CompoundsMolecular Compounds

Two types of compounds: Molecular and IonicTwo types of compounds: Molecular and Ionic Ionic compounds form when two atoms Ionic compounds form when two atoms transfertransfer electrons to other electrons to other

atomsatoms Molecular compounds form when atoms Molecular compounds form when atoms shareshare electrons electrons Molecule is smallest unit of a pure substance (cluster of atoms)Molecule is smallest unit of a pure substance (cluster of atoms) Diatomic molecule is a molecule made of two atoms of the same Diatomic molecule is a molecule made of two atoms of the same

element.element.Eg. O, N, H are all diatomic and thus written as O2, N2, H2Eg. O, N, H are all diatomic and thus written as O2, N2, H2 Most molecular compounds form sm.structures therefore, have Most molecular compounds form sm.structures therefore, have

strong bonds between atoms but very weak bonds between strong bonds between atoms but very weak bonds between molecules.molecules.

As a result, they have low boiling points and low melting pointsAs a result, they have low boiling points and low melting points

Naming Molecular CompoundsNaming Molecular Compounds Compounds are named by IUPAC (international union of pure and Compounds are named by IUPAC (international union of pure and

applied chemistry) recommendations.applied chemistry) recommendations. Binary compounds are made from two elements.Binary compounds are made from two elements. Rules for naming:Rules for naming:

1.1. Write the name of the first elementWrite the name of the first element2.2. Change the ending of the second to “ide”Change the ending of the second to “ide”3.3. Use a prefix to indicate the # of each type of atomUse a prefix to indicate the # of each type of atom

Mono=1 (only used for the second element)Mono=1 (only used for the second element) Di = 2Di = 2 Tri = 3Tri = 3 Tetra = 4Tetra = 4

Eg. COEg. CO22 Carbon Carbon DiDioxoxideide To change from name to chemical formulaTo change from name to chemical formula

1.1. Write the symbol for each element in the same orderWrite the symbol for each element in the same order2.2. Use subscripts to indicate the # of each atom.Use subscripts to indicate the # of each atom.

When naming a compound, often it has sm.symbols in ( ) to indicate the When naming a compound, often it has sm.symbols in ( ) to indicate the state of matter (s), (l), (g) or (aq) which = aqueous (solid dissolved in state of matter (s), (l), (g) or (aq) which = aqueous (solid dissolved in water)water)

Naming Molecular CompoundsNaming Molecular Compounds

Try the following:Try the following:

CO _____________________________CO _____________________________

SiOSiO22__________________________________________________________

Carbon tetrachloride ________________Carbon tetrachloride ________________

Sulfur Dioxide _____________________Sulfur Dioxide _____________________

Naming Molecular CompoundsNaming Molecular Compounds

Try the following:Try the following:

CO CO carbon monoxidecarbon monoxide

SiOSiO2 2 Silicon dioxideSilicon dioxide

Carbon tetrachloride Carbon tetrachloride CClCCl44

Sulfur Dioxide Sulfur Dioxide SOSO22

Ionic CompoundsIonic Compounds

Form when atoms transfer electronsForm when atoms transfer electronsAn ion is formed when an atom gains or An ion is formed when an atom gains or

loses an electron and is no longer neutralloses an electron and is no longer neutral Ions always have a + or – chargeIons always have a + or – chargeWhen dissolved in water ionic compounds When dissolved in water ionic compounds

separate into ions and thus carry an separate into ions and thus carry an electric current.electric current.

Naming Ionic CompoundsNaming Ionic Compounds

Rules are similar to molecularRules are similar to molecular The main difference is the name doesn’t The main difference is the name doesn’t

indicate the #of ions in each element.indicate the #of ions in each element. The Rules:The Rules:

1.1. Name includes both elements with the metallic element Name includes both elements with the metallic element firstfirst

2.2. Non metallic element is second with “ide” endingNon metallic element is second with “ide” ending

3.3. Subscripts indicate the ratio of ions in a compound.Subscripts indicate the ratio of ions in a compound.

Eg. CaClEg. CaCl22 calcium chloride (ratio = 1Ca to 2Cl calcium chloride (ratio = 1Ca to 2Cl

Try the following:Try the following:

NaCl ______________NaCl ______________

LiCl _______________LiCl _______________

Sodium Fluoride ________Sodium Fluoride ________

Zinc Sulfide ____________Zinc Sulfide ____________

Try the following:Try the following:NaCl NaCl sodium chloridesodium chlorideLiCl LiCl Lithium chlorideLithium chlorideSodium Fluoride Sodium Fluoride NaFNaFZinc Sulfide Zinc Sulfide ZnSZnS

Properties of Ionic & MolecularProperties of Ionic & MolecularCompoundsCompounds

IonicIonic MolecularMolecular

Formed from metallic Formed from metallic and non-metallic and non-metallic elementselements

Usually formed from Usually formed from only non-metallic only non-metallic elementselements

Forms ions in solutionForms ions in solution Doesn’t form ions in Doesn’t form ions in solutionsolution

Conducts electricityConducts electricity Non-conductingNon-conducting

Solid at room Solid at room temperaturetemperature

Solid, liquid or gas at Solid, liquid or gas at room temperatureroom temperature

Chemical ReactionsChemical Reactions

Two or more substances combine to form Two or more substances combine to form a new substance. Cannot be reversed.a new substance. Cannot be reversed.

Reactants – substances that go into a Reactants – substances that go into a reaction.reaction.

Products- what is formed in the reactionProducts- what is formed in the reaction

Chemical equationsChemical equations

How chemists describe reactionsHow chemists describe reactionsWord equations and chemical Word equations and chemical

equationsequationsChemical equations use symbolsChemical equations use symbolsEg. Magnesium + oxygen Eg. Magnesium + oxygen

magnesium oxidemagnesium oxideOr 2Mg(s) + OOr 2Mg(s) + O2 2 2 MgO (s) + light 2 MgO (s) + light

Balancing Chemical EquationsBalancing Chemical Equations

Remember the law of conservation of Remember the law of conservation of mass?mass? It says that atoms can’t be lost or created. It says that atoms can’t be lost or created.

The atoms essentially change partners. The atoms essentially change partners. Therefore, you will have the same # of atoms Therefore, you will have the same # of atoms of each element just combined differently.of each element just combined differently.

Eg. HCEg. HC22HH33OO2 (aq) 2 (aq) + NaHCO+ NaHCO33 (s) (s) NaC NaC22HH33OO2 (aq)2 (aq) + H + H22O (l) + COO (l) + CO2 (g)2 (g)

(vinegar) (baking soda)(vinegar) (baking soda) (sodium acetate) + (water) + (Carbon dioxide)(sodium acetate) + (water) + (Carbon dioxide)

Take a minute to add up the number of atoms of each Take a minute to add up the number of atoms of each element on both sides of the equationelement on both sides of the equation

It is important to balance a chemical equation so that each side of It is important to balance a chemical equation so that each side of the equation has the same number of atoms of each element.the equation has the same number of atoms of each element.

To balance an equation you need to count the number of atoms of To balance an equation you need to count the number of atoms of each element on the each side of the equation and make both sides each element on the each side of the equation and make both sides equal by using co-efficiantsequal by using co-efficiants

Eg. Magnesium + oxygen Eg. Magnesium + oxygen magnesium oxidemagnesium oxideStep 1: write the chemical equationStep 1: write the chemical equationMg + OMg + O22 MgO *oxygen is a diatomic molecule MgO *oxygen is a diatomic molecule so it is always written Oso it is always written O22

Step 2: count the # of atoms of each element.Step 2: count the # of atoms of each element.1Mg & 2O1Mg & 2OStep 3: balance the equation: there are 2 O’s on the left so we need 2 Step 3: balance the equation: there are 2 O’s on the left so we need 2

on the right. Mg + Oon the right. Mg + O22 22MgOMgOStep 4: now, we have 2 Mg on the right and only 1 on the left. So, use Step 4: now, we have 2 Mg on the right and only 1 on the left. So, use

a coefficiant. a coefficiant. 22Mg + OMg + O22 2MgO 2MgO

Step 5: count the atoms and make sure eveyone is happy! You now Step 5: count the atoms and make sure eveyone is happy! You now have a balanced equation.have a balanced equation.

BalancingBalancing

Try the following:Try the following:CHCH4 4 +_ O+_ O22 CO CO2 2 +_ H+_ H22OO

_H_H22 + O + O22 _ H _ H22OO

_Na + Cl_Na + Cl22 _NaCl_NaCl

_CaCO_CaCO33 +_ H +_ H22SOSO4 4 _CaSO _CaSO4 4 + _H+ _H22O +_ COO +_ CO2 2

BalancingBalancing

Try the following:Try the following:CHCH4 4 +2+2 O O22 CO CO2 2 ++22 H H22OO

22HH22 + O + O22 22 H H22OO

22Na + ClNa + Cl22 22NaClNaCl

_CaCO_CaCO33 +_ H +_ H22SOSO4 4 _CaSO _CaSO4 4 + _H+ _H22O +_ COO +_ CO2 2

Breaking Chemical BondsBreaking Chemical Bonds

Chemical bonds are forces that cause a group of Chemical bonds are forces that cause a group of atoms to behave as a unit.atoms to behave as a unit.

To break these bonds, energy must be added.To break these bonds, energy must be added. When bonds form energy is releasedWhen bonds form energy is released Energy is produced or absorbed during a Energy is produced or absorbed during a

reaction.reaction. Exothermic reactions- eg. combustionExothermic reactions- eg. combustion Endothermic reactions eg. Baking cookies; baking soda Endothermic reactions eg. Baking cookies; baking soda

breaks down and release CO2 and puffs up the cookiesbreaks down and release CO2 and puffs up the cookies Eg. Corrosion – prevent by zinc / galvanizationEg. Corrosion – prevent by zinc / galvanization

Reaction RateReaction Rate

You can increase or decrease the rate of a You can increase or decrease the rate of a reaction by:reaction by:

Changing the temp.Changing the temp. StirringStirring Changing size and conc. Of reactantsChanging size and conc. Of reactants

Catalysts – speed up a reaction without being Catalysts – speed up a reaction without being changed changed

Eg. Enzymes – these occur naturally in our bodies. Saliva Eg. Enzymes – these occur naturally in our bodies. Saliva (contains enzymes) helps breaks down the starches in our (contains enzymes) helps breaks down the starches in our foodfood

Inhibiter – slows down the reactionInhibiter – slows down the reactionEg. Preservatives in food.Eg. Preservatives in food.

Quick Note:Quick Note:Memorize the chemical names of common Memorize the chemical names of common

chemicals. These are found on pg 442 -445 in chemicals. These are found on pg 442 -445 in your text. This will be on your midterm!your text. This will be on your midterm!

You should know the chemical formula’s for the You should know the chemical formula’s for the following:following:

VinegarVinegar Table saltTable salt PropanePropane Sugar (sucrose)Sugar (sucrose) GlucoseGlucose Hydrogen peroxideHydrogen peroxide