CHEMISTRY Patterns and Compounds. 5.1 Looking for Patterns in Chemical Reactivity Valence Shell –...

CHEMISTRYCHEMISTRY

Patterns and CompoundsPatterns and Compounds

5.1 Looking for Patterns in 5.1 Looking for Patterns in Chemical ReactivityChemical Reactivity

Valence Shell – The outermost electron Valence Shell – The outermost electron shell that an atom has.shell that an atom has.

Valence Electrons – the electrons found in Valence Electrons – the electrons found in the atom’s valence shell.the atom’s valence shell.

Steam Boat DemoSteam Boat Demo

1.1. PreparationPreparation Using a dropper fill the tubes and diaphragm Using a dropper fill the tubes and diaphragm

with waterwith water Place the boat in the waterPlace the boat in the water Place and lit a candle under the diaphragmPlace and lit a candle under the diaphragm

2.2. Explain diaphragm expansionExplain diaphragm expansion When heated the water particles move When heated the water particles move

fasterfaster This increases the space between particlesThis increases the space between particles

This causes an increase in pressure, This causes an increase in pressure, pushing the tin uppushing the tin up

A change of state occurs (vaporization), the A change of state occurs (vaporization), the water turns to steam (volume increases water turns to steam (volume increases 1600 times)1600 times)

3.3. What causes flattening of the What causes flattening of the diaphragm?diaphragm?

As the steam escapes, a vacuum is created.As the steam escapes, a vacuum is created. This causes water to be “sucked” in and the This causes water to be “sucked” in and the

cycle repeats itself causing a “putt, putt” cycle repeats itself causing a “putt, putt” soundsound

4.4. What propels the boat?What propels the boat? The escaping steam leaves the exhaust pipe The escaping steam leaves the exhaust pipe

with great force.with great force. For every action, there is an equal and For every action, there is an equal and

opposite reaction.opposite reaction. This pushes the boat forward.This pushes the boat forward.

5.5. External Combustion Engine?External Combustion Engine? The heat source is “outside” of the engineThe heat source is “outside” of the engine Contrast with internal combustion engineContrast with internal combustion engine

Controlled explosion in a cylinderControlled explosion in a cylinder

Chemical ReactionsChemical Reactions

AtomsAtoms NEVER gain or lose protons. (if they did we NEVER gain or lose protons. (if they did we

could make gold) could make gold) AAlmost NEVER gain or lose neutrons. (OK lmost NEVER gain or lose neutrons. (OK

radioactive elements do) radioactive elements do) Often gain or lose valence electrons. The Often gain or lose valence electrons. The

number of valence electrons give the element number of valence electrons give the element it’s physical and chemical properties.it’s physical and chemical properties.

Atomic Diagrams Atomic Diagrams (draw Na diagrams below)(draw Na diagrams below)

Bohr-Rutherford DiagramBohr-Rutherford Diagram /Lewis Dot Diagram/Lewis Dot Diagram

(Electron Dot (Electron Dot Diagram)Diagram)

Since only the valence eSince only the valence e-- matter for properties, it matter for properties, it becomes a waste of time to draw other electrons. becomes a waste of time to draw other electrons.

Lewis Dot Diagrams are faster and easier to draw, Lewis Dot Diagrams are faster and easier to draw, and they show all the important information.and they show all the important information.

Drawing Lewis Diagrams:Drawing Lewis Diagrams:

1)1) Write the element’s symbolWrite the element’s symbol

2)2) Draw the valence electrons Draw the valence electrons

clockwise around the symbol.clockwise around the symbol.

Read and complete p. 145 in the space below

IONSIONS

Keep an eye-on those electrons!! Keep an eye-on those electrons!! Key Eye-dea: Atoms don’t want valence Key Eye-dea: Atoms don’t want valence

shells partly full. shells partly full.

CationsCations positively charged atoms that have lost positively charged atoms that have lost

electron(s).electron(s). Alkali MetalsAlkali Metals (1 valence e (1 valence e--) )

easily LOSE the eeasily LOSE the e--

Very reactiveVery reactive BBC/OU Open2.net - The World Around BBC/OU Open2.net - The World Around

Us - Alkali metalsUs - Alkali metals Alkaline Earth MetalsAlkaline Earth Metals (2 valence e (2 valence e--) )

Not as easy to lose 2 eNot as easy to lose 2 e--.. ReactiveReactive

CationsCations Reactivity increases down the family Reactivity increases down the family

(group) because of the higher distance (group) because of the higher distance from efrom e-- to proton(+). to proton(+). It’s easier to lose the eIt’s easier to lose the e- - if it is farther from the if it is farther from the

nucleus (higher energy level).nucleus (higher energy level). Metals form cations.Metals form cations.

AnionsAnions

Negatively charged atoms that have Negatively charged atoms that have gained one or more electron(s)gained one or more electron(s)

HalogensHalogens (7 valence e (7 valence e--) TAKE electrons ) TAKE electrons forcefully!!forcefully!!

Non-metals form anions.Non-metals form anions. Chalcogens (6 valence eChalcogens (6 valence e--))

more difficult to take two electronsmore difficult to take two electrons

AnionsAnions

Noble Gases – don’t react with other Noble Gases – don’t react with other atoms because their valence shells are atoms because their valence shells are

already full.already full.

REMEMBER:REMEMBER:

Ca+ions are posi+ive. Ca+ions are posi+ive.

AAnnions are ions are nnegative.egative.

AssignmentAssignment

Do pg 146 #1 – 6 and BLM’s 5-1, 5-2, 5-6, Do pg 146 #1 – 6 and BLM’s 5-1, 5-2, 5-6, 5-75-7, 5-9 and 5-10, 5-9 and 5-10

5.2 - 5.2 - AtomsAtoms vs. Ions vs. Ions

Atoms Atoms # of protons = # of electrons# of protons = # of electrons neutral chargeneutral chargeIonsIons atoms which have gained or lost electronsatoms which have gained or lost electrons have charges on themhave charges on them

5.2 - 5.2 - AtomsAtoms vs. Ions vs. Ions

Ex. If Mg loses 2 electrons it becomes Ex. If Mg loses 2 electrons it becomes

(Remember meta(Remember metaLLs s LLose electrons)ose electrons)

Ex. If Cl gains 1 electron it becomes Ex. If Cl gains 1 electron it becomes

(non-metals gain electrons)(non-metals gain electrons)

Chemical BondingChemical Bonding

Note:Note:

Atoms always bond with each Atoms always bond with each other through the valence electrons. other through the valence electrons.


There are 3 ways in which atoms bond:There are 3 ways in which atoms bond:1.1. Ionic bondsIonic bonds – between metals and – between metals and

non-metals.non-metals. Metals happily Metals happily transfertransfer their electrons their electrons

to non-metals which happily accept to non-metals which happily accept the electrons.the electrons.

Electrons transfer making two Electrons transfer making two oppositely charged IONS which stick oppositely charged IONS which stick together.together.


1.1. Ionic bondsIonic bonds (cont’d) (cont’d) Ionic compoundsIonic compounds are formed. are formed. Ionic compounds:Ionic compounds:

have high melting points. (strong ionic have high melting points. (strong ionic bonds)bonds)

dissolve easily in water.dissolve easily in water. are electrolytes – materials that conduct are electrolytes – materials that conduct

electricity when molten or when dissolved electricity when molten or when dissolved (aqueous).(aqueous).

Lewis Diagrams for Bonding:Lewis Diagrams for Bonding:Ionic BondingIonic Bonding – atoms become ions. – atoms become ions. Metal atom donates eMetal atom donates e-- to non-metal to non-metal

atom. X denotes donated eatom. X denotes donated e--..

. . XX ..

LiLi HHFill in the dots belowFill in the dots below

[ [ Li Li ]]++ [[ H H ]]--

Lewis Diagrams for Bonding:Lewis Diagrams for Bonding:If the metal needs to donate 2 eIf the metal needs to donate 2 e--, it may , it may

need to find 2 atoms to accept one each. need to find 2 atoms to accept one each.

Fill in the missing electrons below.Fill in the missing electrons below.

Cl Mg Cl Cl Mg Cl

[[ Cl Cl ]]-- [[ Mg Mg ]]2+2+ [[ Cl Cl ]]--

Lewis Diagrams for Bonding:Lewis Diagrams for Bonding:

OR find a non-metal that will take 2 e-OR find a non-metal that will take 2 e-Fill in the missing electrons.Fill in the missing electrons.

[[ MgMg ]]2+2+ [[ OO ]]2-2-

The charge that the ion has is often referred The charge that the ion has is often referred to as the combining capacity of the ion. to as the combining capacity of the ion.

Try: HCl Try: HCl


2.2. Covalent bondsCovalent bonds – between two non- – between two non-metals.metals.

Electrons are Electrons are sharedshared by the non- by the non-metals.metals.

Sharing electrons allows each atom to Sharing electrons allows each atom to have a full shell for short periods of have a full shell for short periods of time.time.


2.2. Covalent bonds (cont’d)Covalent bonds (cont’d) Molecular compounds Molecular compounds are formed.are formed. molecular compounds:molecular compounds:

have low melting points (weaker bonds)have low melting points (weaker bonds) don’t conduct electricitydon’t conduct electricity don’t dissolve as easily in water. don’t dissolve as easily in water.


2.2. Covalent bonds (cont’d)Covalent bonds (cont’d) there are 2 types of covalent bonds:there are 2 types of covalent bonds:

a)a) polar covalentpolar covalent – the atoms are different – the atoms are different elements. Electrons are not shared elements. Electrons are not shared evenly by the atoms. One atom gets the evenly by the atoms. One atom gets the electrons for a longer time. Ex) Helectrons for a longer time. Ex) H22OO

• H is the positive pole and O is the negative H is the positive pole and O is the negative pole.pole.


2.2. Covalent bonds (cont’d)Covalent bonds (cont’d)b)b) Non-polar covalentNon-polar covalent – the electrons are – the electrons are

shared evenly because both atoms are shared evenly because both atoms are the same element. Ex) Nthe same element. Ex) N22, O, O22, F, F22, Cl, Cl22, ,

BrBr22, I, I22 are the only examples. They are are the only examples. They are

called diatomic molecules. See the “7” called diatomic molecules. See the “7” pattern in the periodic table. pattern in the periodic table.

• HOFBrINCl the clownHOFBrINCl the clown


Covalent BondingCovalent Bonding – non-metals share – non-metals share electrons. Line up atoms so that they electrons. Line up atoms so that they can fill each others outer shells. Circle sharedcan fill each others outer shells. Circle sharedpairs.pairs.

HH22O H O HO H O H

O has 6 valence eO has 6 valence e--, H has 1, H has 1


Try:Try:

CHCH44, Br, Br22, O, O22

We will draw covalent bonds as follows:We will draw covalent bonds as follows:

HH H – C – H H – C – H Br – Br Br – Br O = OO = O

HH


3.3. Metallic bonding – Metallic bonding – between atoms between atoms that are metals.that are metals.

Metals allow their electrons to be juggled Metals allow their electrons to be juggled back and forth from one atom to the next.back and forth from one atom to the next.

Electricity: eElectricity: e-- easily move from atom to easily move from atom to atom.atom.

Comparing Types of BondingComparing Types of BondingIonicIonic CovalentCovalent MetallicMetallic

Called Called ionic compoundsionic compounds Called Called molecular compoundsmolecular compounds Names with the metal nameNames with the metal name

Metals with non-metalsMetals with non-metals Non-metals onlyNon-metals only Metals onlyMetals only

Metals donate e- to non-Metals donate e- to non-metals forming oppositely metals forming oppositely charged ions which stickcharged ions which stick

Non-metals share e- so that Non-metals share e- so that for at least some of the time for at least some of the time they will have 8e-they will have 8e-

Metals play “hot potato” with Metals play “hot potato” with e- so e- can flow freely from e- so e- can flow freely from one atom to the next.one atom to the next.

The overall cation charges The overall cation charges must balance with the anion must balance with the anion charges.charges.Ex)Ex)MgMg+2+2 with Cl with Cl-- means we have means we haveMgClMgCl22

Two types of sharingTwo types of sharing 1) non-polar covalent – 1) non-polar covalent –

sharing of e- is fair. sharing of e- is fair. Occurs in diatoms NOccurs in diatoms N22, O, O22, ,

FF22, Cl, Cl22, Br, Br22, H, H22, I, I22

2) polar covalent – sharing 2) polar covalent – sharing of e- is unfair. One atom of e- is unfair. One atom hogs electrons more than hogs electrons more than the other. Ex) Hthe other. Ex) H22OO

Good for wires. Add an e- to Good for wires. Add an e- to one end and another will pop one end and another will pop out the other end.out the other end.

Very high melting pointVery high melting point Are often liquids or gasesAre often liquids or gases SolidsSolids

MOSTLY dissolve in water. MOSTLY dissolve in water. Ions break apart.Ions break apart.

Polar solutes dissolve in polar Polar solutes dissolve in polar solventssolventsNon-polar solutes dissolve in Non-polar solutes dissolve in non-polar solventsnon-polar solvents

Don’t tend to dissolveDon’t tend to dissolve

Conduct electricity when Conduct electricity when dissolved or when molten dissolved or when molten (Electrolytes)(Electrolytes)

Don’t conduct electricity very Don’t conduct electricity very well.well.

Conduct electricity very well.Conduct electricity very well.

http://rlv.zcache.com/war_of_the_atoms_poster-p228361748241900516tdcp_400.jpg

http://www.lab-initio.com/screen_res/nz063.jpg


Do P 154 2-4 and BLM 5.8 – 5.11 & 5.13Do P 154 2-4 and BLM 5.8 – 5.11 & 5.13

5.3 Naming Binary Ionic 5.3 Naming Binary Ionic CompoundsCompounds

Binary – having only 2 types of atomsBinary – having only 2 types of atoms Ionic Compounds – electrons are Ionic Compounds – electrons are

transferred from metals to non-metals. transferred from metals to non-metals. The ions stick together. (pg 148-149 The ions stick together. (pg 148-149 diagrams)diagrams)

Reading the Name from the formula:Reading the Name from the formula:

1)1) Binary compounds usually end it “ide”.Binary compounds usually end it “ide”.

2)2) Write cation first and anion second Write cation first and anion second adding “ide” to the anion.adding “ide” to the anion.

Examples: Examples: CaClCaCl22 is called Calcium Chloride is called Calcium Chloride

MgBrMgBr22 is called Magnesium Bromide is called Magnesium Bromide

Writing the formula from the name:Writing the formula from the name:

1)1) Determine that the compound is ionic.Determine that the compound is ionic. (metal and a non-metal.) Eg. Calcium (metal and a non-metal.) Eg. Calcium

& Chlorine& Chlorine

2)2) Temporarily mark the combining Temporarily mark the combining capacity (charge) on each atom. Eg. capacity (charge) on each atom. Eg. CaCa2+2+ Cl Cl --

Note: in case of a charge of 1 the number Note: in case of a charge of 1 the number 1 is assumed1 is assumed


3)3) Do a “crossover” with the combining Do a “crossover” with the combining capacities.capacities.

The 1 from Cl moves to a subscript on The 1 from Cl moves to a subscript on the Ca, and the 2+ on one Ca ion moves the Ca, and the 2+ on one Ca ion moves to the subscript on the Cl ion.to the subscript on the Cl ion.

4)4) Write the number of atoms needed as Write the number of atoms needed as a subscript. Note: Cations get written a subscript. Note: Cations get written first.first.

CaClCaCl22

Ionic “Dating” ActivityIonic “Dating” Activity

Transition MetalsTransition Metals

Each of these metals can form more than Each of these metals can form more than

one cation.one cation.

Eg. Fe can form FeEg. Fe can form Fe2+2+ and Fe and Fe3+3+. They are . They are located in the middle region of the located in the middle region of the periodic table.periodic table.

Classical NamingClassical Naming

1)1) Use the latin name for the atom. Use the latin name for the atom. Fe is ferrum in Latin.Fe is ferrum in Latin.

a. Use suffix “ous” for the lesser charge a. Use suffix “ous” for the lesser charge ion. Feion. Fe2+2+ is is ferrous.ferrous.

b. Use suffix “ic” for the greater charged b. Use suffix “ic” for the greater charged ion. Feion. Fe3+3+ is is ferricferric..

Eg. Ferrous Sulfate would contain the Eg. Ferrous Sulfate would contain the FeFe2+2+ ion. ion.

Stock Naming System:Stock Naming System:

Use roman numerals to show the Use roman numerals to show the charge on the cation.charge on the cation.

Eg. FeClEg. FeCl33 is iron(III) chloride is iron(III) chloride

Assignment:Assignment:

BLM 5.14 – use page 156 #1 – 13 as a BLM 5.14 – use page 156 #1 – 13 as a guideguide

Naming Naming CompoundsCompoundsIonic Compounds Molecular Compounds

Binary Polyatomic

-Ends in “ide”-metal is named first-Balance the number of charges.Ca2+ and Cl- → CaCl2

-Ends in “ate”-Charge is on a group of atoms.-Balance the number of charges.NH4

+ and S2- →

(NH4)2S

-Ends in “ide”-element from left on chart is named first-use number prefixes-mono - 1-di - 2-tri - 3-tetra - 4-penta - 5-hexa - 6Eg) N2O3 – dinitrogen trioxide

Transition metal

-Find the charge on the metal, using the known charge on the non-metal.

-Classic Naming ↓ charge “ous”, ↑ charge “ic”-Stock NamingEg) FeCl2 has Fe2+ - ferrous chloride

orIron (II) chloride.Eg) FeCl3 has Fe3+ - ferric chloride or

iron (III) chloride.

Naming Polyatomic Ionic Naming Polyatomic Ionic CompoundsCompounds

Poly – manyPoly – many Polyatomic/Complex Ions – Ions which Polyatomic/Complex Ions – Ions which

have more than one type of element in have more than one type of element in them (see top of yellow sheet)them (see top of yellow sheet) the ionic charge is on the entire group of the ionic charge is on the entire group of

atoms.atoms.

Ex) (NOEx) (NO33))-- is a group of atoms which has an is a group of atoms which has an

extra electron.extra electron. Note: the nitrogen and oxygen atoms have Note: the nitrogen and oxygen atoms have

covalent bonds.covalent bonds.

Naming Polyatomic Ionic Naming Polyatomic Ionic CompoundsCompounds

Common polyatomic ions:Common polyatomic ions: ammonium, (NHammonium, (NH44))++

nitrate, (NO)nitrate, (NO)3-3-

sulfate, (SO)sulfate, (SO)442-2-

carbonate, (COcarbonate, (CO33))2-2-

phosphate, (POphosphate, (PO44))3-3-

hydroxide, (OH)hydroxide, (OH)--

perchlorate, (ClO)perchlorate, (ClO)4-4-

Reading the name from the Reading the name from the formula:formula:

1.1. In compounds where the anion is In compounds where the anion is polyatomic, the names end in “ate” or “ite”.polyatomic, the names end in “ate” or “ite”.

A few exceptions Hydroxide OHA few exceptions Hydroxide OH--

2.2. Write cation first and anion second.Write cation first and anion second.

Examples:Examples: Ca(SOCa(SO44) is called calcium sulfate) is called calcium sulfate

(NH(NH44))22S is called ammonium sulfS is called ammonium sulfideide (Note: “ide” because anion isn’t polyatomic)(Note: “ide” because anion isn’t polyatomic)


If the cation is a transition metal:If the cation is a transition metal:

1.1. Determine the charge on the cation by Determine the charge on the cation by reverse crossover.reverse crossover.

E.g. FeE.g. Fe22OO33

FeFe22 OO33

3+ 2-

Iron (III) Oxide


2.2. Give the charge of the cation in the name.Give the charge of the cation in the name.a)a) Use stock naming (Roman Numerals) on Use stock naming (Roman Numerals) on

cation.cation. Roman numeral gives the charge of the cationRoman numeral gives the charge of the cation

E.g. Iron(II) Oxide is the FeE.g. Iron(II) Oxide is the Fe2+2+ ion ion FeOFeO

Iron (III) Oxide is the Fe Iron (III) Oxide is the Fe 3+3+ ion ion FeFe22OO33

b)b) Use Classical naming Use Classical naming ““ous” ending for lesser charge.ous” ending for lesser charge. ““ic” ending for greater charge.ic” ending for greater charge.


Example: CuCOExample: CuCO33

Cu(COCu(CO33))2-2- what charge does Cu have for what charge does Cu have for

the crossover to make CuCOthe crossover to make CuCO33??

Cu2+Cu2+ So CuCO3 is So CuCO3 is Copper (II) CarbonateCopper (II) Carbonate

(Note: Cu+ exists, so we must have the greater (Note: Cu+ exists, so we must have the greater ion)ion)

or or Cupric CarbonateCupric Carbonate..


Use the crossover just like with binary Use the crossover just like with binary ionic compounds.ionic compounds.

Be careful to apply the combining Be careful to apply the combining capacities to the entire ions. capacities to the entire ions.

Ex) Magnesium PhosphateEx) Magnesium Phosphate

Mg Mg 2+2+(PO(PO44))3-3-

MgMg33(PO(PO44))22


Example: Copper (I) SulphateExample: Copper (I) Sulphate

CuCu1+1+ (SO (SO44))2-2-

CuCu22(SO(SO44))

Naming Molecular Naming Molecular CompoundsCompounds

Molecular compounds – 2 non-metals Molecular compounds – 2 non-metals (Covalent bonds)(Covalent bonds)

end in “ide” like binary ionic.end in “ide” like binary ionic. prefixes are used to describe the number prefixes are used to describe the number

of each atom present in a molecule.of each atom present in a molecule.


Prefix Number Prefix Number mono 1 hexa 6 di 2 hepta 7 tri 3 octa 8 tetra 4 nona 9 penta 5 deca 10


Steps to naming:Steps to naming: Determine if the compound is ionic or molecularDetermine if the compound is ionic or molecular Start with the element to the left on the periodic Start with the element to the left on the periodic

table.table. Describe the number of atoms using prefixesDescribe the number of atoms using prefixes

NOTE: mono is often left out and used only when NOTE: mono is often left out and used only when necessary to describe the compound.necessary to describe the compound.

Example: COExample: CO22 – carbon dioxide – carbon dioxide

NN22O – dinitrogen monoxideO – dinitrogen monoxide

NN22OO33 – dinitrogen trioxide – dinitrogen trioxide


BLM 5.14 - 5.17BLM 5.14 - 5.17

5.4 Chemical Formulas and 5.4 Chemical Formulas and EquationsEquations

The law of The law of conservation of massconservation of mass: : Atoms are neither created, nor Atoms are neither created, nor

destroyed, during any chemical destroyed, during any chemical reactionreaction

The same atoms that exist before a The same atoms that exist before a chemical reaction are present after a chemical reaction are present after a reaction. They are simply rearranged reaction. They are simply rearranged during a reaction.during a reaction.

Chemical EquationsChemical Equations

Chemical reactions are represented on Chemical reactions are represented on paper by paper by chemical equationschemical equations. .

For example, hydrogen gas (H2) can react For example, hydrogen gas (H2) can react (burn) with oxygen gas (O2) to form water (burn) with oxygen gas (O2) to form water (H20). (H20).

The The chemical equationchemical equation for this for this reactionreaction is is written as:written as:

The The chemical equationchemical equation for this for this reactionreaction is is written as:written as:

Coefficients give the number of molecules, Coefficients give the number of molecules, while subscripts give the number of atoms in while subscripts give the number of atoms in each molecule.each molecule.

Reactants are on the left and products on the Reactants are on the left and products on the rightright

A chemical equation must be ‘balanced’ by A chemical equation must be ‘balanced’ by having an equal number of atoms of each having an equal number of atoms of each element on each side of the arrowelement on each side of the arrow..

Steps:Steps:

1.1. Write 'skeleton' equation using formulas of Write 'skeleton' equation using formulas of reactants and products. List molecules reactants and products. List molecules only.only.

2.2. Write 'balanced' equation by determining Write 'balanced' equation by determining coefficients that provide equal numbers of coefficients that provide equal numbers of each type of atom on each side of the each type of atom on each side of the equation (whole number values). equation (whole number values).

Look at most complicated molecules first and Look at most complicated molecules first and simplest last.simplest last.

Note: Subscripts should never be changed.Note: Subscripts should never be changed.

Example: Methane (CH4) burns in air. Example: Methane (CH4) burns in air. The uses oxygen (O2) and produces water The uses oxygen (O2) and produces water (H2O) and carbon dioxide (CO2). (H2O) and carbon dioxide (CO2).

Count up the atoms in the reactants and Count up the atoms in the reactants and products: products:

Carbon atoms are balanced, but we have Carbon atoms are balanced, but we have only half the # of hydrogens in our only half the # of hydrogens in our products as in our reactants. We can fix products as in our reactants. We can fix this by doubling the relative number of this by doubling the relative number of water molecules in the list of products: water molecules in the list of products:

Note that while this has balanced our Note that while this has balanced our carbon and hydrogen atoms, we now have carbon and hydrogen atoms, we now have 4 oxygen atoms in our products, and only 4 oxygen atoms in our products, and only have 2 in our reactants. We can balance have 2 in our reactants. We can balance our oxygen atoms by doubling the number our oxygen atoms by doubling the number of oxygen atoms in our reactants: of oxygen atoms in our reactants:

Balance the chemical equationBalance the chemical equation for the for the reaction of methane(CHreaction of methane(CH44) with oxygen ) with oxygen

(O(O22). Thus, ). Thus, one molecule of methane one molecule of methane

reacts with two molecules of oxygen to reacts with two molecules of oxygen to produce one molecule of carbon dioxide produce one molecule of carbon dioxide and two molecules of waterand two molecules of water..

The physical state of each chemical can The physical state of each chemical can be indicated by using the symbols (be indicated by using the symbols (gg) gas, ) gas, ((l) liquidl) liquid, and (, and (s) solid, (aq) aqueous s) solid, (aq) aqueous (dissolved) (dissolved)

In general, when balancing reactions you In general, when balancing reactions you should focus on the most complex should focus on the most complex molecules first. molecules first.

Finally, balance out your reaction using Finally, balance out your reaction using the simplest molecules.the simplest molecules.


BLM 5.18 – 5.20, Balancing Chemical BLM 5.18 – 5.20, Balancing Chemical Equations Practice 1 & 2Equations Practice 1 & 2

Chapter Review – BLM 5.21 & 5.22Chapter Review – BLM 5.21 & 5.22

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