Chemistry Unit NotesChemistry Unit Notes88thth Grade Science Grade Science

Basic VocabularyBasic Vocabulary

MatterMatter: Anything that has mass and volume: Anything that has mass and volume

MassMass: Amount of matter in an object: Amount of matter in an object

WeightWeight: Measure of the force of attraction : Measure of the force of attraction between objects due to mass and gravitybetween objects due to mass and gravity

VolumeVolume: Amount of space an object takes up: Amount of space an object takes up

DensityDensity: Measurement of how much mass is : Measurement of how much mass is contained in a given volumecontained in a given volume

More VocabularyMore Vocabulary

Atoms:Atoms: Smallest particle of an element that has all Smallest particle of an element that has all the properties of matter:the properties of matter:

– Protons-Protons- particles in the nucleus with positive charge particles in the nucleus with positive charge– Electrons-Electrons- particles orbiting around nucleus with negative particles orbiting around nucleus with negative

chargecharge– Neutrons-Neutrons- particles in the nucleus with no charge particles in the nucleus with no charge

ElementsElements: Simplest form of a pure substance: Simplest form of a pure substance CompoundsCompounds: Two or more elements chemically : Two or more elements chemically

combined to form a new substancecombined to form a new substance

Sub-Atomic ParticlesSub-Atomic Particles

Part of Part of AtomAtom

ChargeCharge LocationLocation Mass/SizeMass/Size

ElectronElectron - negative- negative outside outside nucleusnucleus

.0006 amu.0006 amu(too little to (too little to count)count)

ProtonProton + positive+ positive inside inside nucleusnucleus

1 amu1 amu

NeutronNeutron no chargeno charge inside inside nucleusnucleus

1 amu1 amu

Periodic TablePeriodic Table

Using the Periodic TableUsing the Periodic Table Atomic NumberAtomic Number

– Equal to # protons = # electronsEqual to # protons = # electrons– Periodic Table is arranged by this Periodic Table is arranged by this

numbernumber

Symbol Symbol – ““Shorthand” for the element – Note 2Shorthand” for the element – Note 2ndnd letter letter

is always lowercaseis always lowercase

Atomic Mass NumberAtomic Mass Number – Total AVERAGE mass of Protons + Neutrons Total AVERAGE mass of Protons + Neutrons

+ Electrons+ Electrons

17

Cl

35.5

Electron Energy LevelsElectron Energy Levels Electrons are arranged in “Shells” around nucleus Electrons are arranged in “Shells” around nucleus

in predictable locationsin predictable locations Fill “seats” closest to nucleus first (concert – best Fill “seats” closest to nucleus first (concert – best

seats)seats) ““Seats” availableSeats” available

– Shell #1Shell #1 2 electrons2 electrons– Shell #2Shell #2 8 electrons8 electrons– Shell #3Shell #3 8 electrons8 electrons– Shell #4 Shell #4 18 electrons18 electrons– Shell #5 Shell #5 32 electrons32 electrons– Shell #6Shell #6 50 electrons50 electrons

Ex. Carbon has 6 total electrons so…Ex. Carbon has 6 total electrons so…Two electrons on first energy level

Four electrons on second energy level

Question: Could we fit more electrons on the second energy level if there were more electrons in carbon??

Atomic StructureAtomic Structure

17

Cl

35.5

Total Mass of Nucleus36 - 17 = 18 neutrons

Element NameChlorine

Total # of protons and electrons (in a neutral atom)17 protons in nucleus17 electrons orbiting nucleus

Notice: electrons follow energy level rules from previous slide.

(Round Atomic Mass)

Atomic Mass – Fractions?Atomic Mass – Fractions?

Look at Chlorine (atomic number 17)Look at Chlorine (atomic number 17) Atomic mass of 35.5? I dont’ get it!Atomic mass of 35.5? I dont’ get it! Where does the 35Where does the 35.5 .5 come from?come from?

– 0.5 protons? 0.5 neutrons? 0.5 protons? 0.5 neutrons? No No

Atomic Mass = Atomic Mass = averageaverage number of number of protons and neutrons in natureprotons and neutrons in nature

More PracticeMore Practice

Determine the name, number of Determine the name, number of protons, neutrons and electrons for protons, neutrons and electrons for each element shown and draw…each element shown and draw…

15

P

31

8

O

16

26

Fe

56

IsotopesIsotopes

An isotope is a variation of an An isotope is a variation of an element (same protons) but can element (same protons) but can have diff. # of neutronshave diff. # of neutrons

Ex: carbon (atomic mass = Ex: carbon (atomic mass = 12.011)12.011)– Carbon (14) and carbon (12) exist in Carbon (14) and carbon (12) exist in

nature nature

IonsIons Change in Change in electronselectrons which gives an which gives an

atom a atom a charge (+ or -)charge (+ or -) You can only add or subtract You can only add or subtract

electrons! electrons! (protons don’t change)(protons don’t change)

– Ex. Ex. Count the number of electrons below…Count the number of electrons below…

Carbon ion (-1 charge)7 electrons (-)6 protons (+)

Carbon ion (+1 charge)5 electrons (-)6 protons (+)

Neutral Carbon6 electrons (-)6 protons (+)

Valence ElectronsValence Electrons An electron on the outermost energy shell of An electron on the outermost energy shell of

an atoman atom Important to understand because this is a key Important to understand because this is a key

factor in how atoms will factor in how atoms will BONDBOND with each other with each other Octet rule – stable atom will have 8 electrons Octet rule – stable atom will have 8 electrons

in that outer shellin that outer shell Practice – Valence # of Practice – Valence # of

– Chlorine?Chlorine?– Neon?Neon?– Nitrogen?Nitrogen?– Oxygen?Oxygen?

Electron Dot DiagramsElectron Dot Diagrams

a diagram that represents the # of a diagram that represents the # of valence electrons in an atom of an valence electrons in an atom of an element.element.

The amount of electrons is displayed by The amount of electrons is displayed by dots around the symbol of the element. dots around the symbol of the element.

Ex.Ex.

http://www.fordhamprep.org/gcurran/sho/http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson38.htmsho/lessons/lesson38.htm

Types of Chemical BondsTypes of Chemical Bonds IonicIonic- - Two elements bond by Two elements bond by transferringtransferring electrons to electrons to

create ions that attract together (+ is attracted to - after an create ions that attract together (+ is attracted to - after an electron is transferred)electron is transferred)

CovalentCovalent- - Two elements bond by Two elements bond by sharingsharing electrons electrons (strongest bond type)(strongest bond type)

MetallicMetallic- - Two metals bond and form a “common electron Two metals bond and form a “common electron cloud”. This is a cluster of shared electrons (weakest bond cloud”. This is a cluster of shared electrons (weakest bond type)type)

Examples of BondingExamples of Bonding

http://www.youtube.com/watch?v=xTx_DWboEVs

http://www.youtube.com/watch?v=1wpDicW_MQQ

http://www.youtube.com/watch?v=QqjcCvzWwww

http://lc.brooklyn.cuny.edu/smarttutor/core3_22/Bonds.html

Predicting BondsPredicting Bonds

Ionic Bond = metal to non-metalIonic Bond = metal to non-metal Covalent = non-metal to non-metalCovalent = non-metal to non-metal Metallic = metal to metalMetallic = metal to metal

Do you understand why? HINT: the numbers at the top of the table indicate the # of valence electrons for each column

Oxidation NumbersOxidation Numbers Oxidation numbers are assigned to each elementOxidation numbers are assigned to each element

They represent a predicted “charge” of an atom/ion when They represent a predicted “charge” of an atom/ion when it bonds with another element.it bonds with another element.

(tells us if the atom would prefer give or take electrons, and how many).(tells us if the atom would prefer give or take electrons, and how many).

They help us to predict what compounds will form when They help us to predict what compounds will form when two elements get together.two elements get together.

Oxidation numbers are labeled like this:Oxidation numbers are labeled like this: Na Na 1+1+

O O 2-2-

How to Use Oxidation How to Use Oxidation NumbersNumbers

Oxidation Number indicates the number of electrons lost, gained or shared when bonding with other atoms.

Ex. Na wants to lose an electron. If an electron is lost, it becomes a +1 charge

SO: oxidation number for Na = 1+

Ex. Cl wants to gain an electron. If an electron is gained, it becomes a -1 charge

SO: oxidation number for Cl = 1-

Oxidation NumbersOxidation Numbers

Each column going down the periodic Each column going down the periodic table has elements with the same table has elements with the same oxidation number.oxidation number.

Label the oxidation numbers on your periodic table at the top of Label the oxidation numbers on your periodic table at the top of each column as shown here:each column as shown here:

1+ 2+ 3+ 4(+/-) 3- 2- 1- 0

Rules for using oxidation Rules for using oxidation numbers to create numbers to create

compoundscompounds1.1. Positive ions can only bond with negative ions and vice Positive ions can only bond with negative ions and vice

versaversa2. The sum of the oxidation numbers of the atoms in a 2. The sum of the oxidation numbers of the atoms in a

compound must be compound must be zero zero (the key is to stay balanced)(the key is to stay balanced)

3. If the oxidation numbers are not equal to zero, then you 3. If the oxidation numbers are not equal to zero, then you must add additional elements until they balance at zero.must add additional elements until they balance at zero.

4. When writing a formula the symbol of the Positive (+) 4. When writing a formula the symbol of the Positive (+) element is followed by the symbol of the negative (-) element is followed by the symbol of the negative (-) element. element.

Examples of Forming Examples of Forming CompoundsCompounds

Ex. Na (+1) + Cl (-1) = NaClEx. Na (+1) + Cl (-1) = NaClAre these oxidation numbers already equal to zero? Are these oxidation numbers already equal to zero? If so, you don’t need to add any extra elements to combine them into a compound, so the answer is If so, you don’t need to add any extra elements to combine them into a compound, so the answer is simply NaClsimply NaCl

Ex. H (+1) + O (-2) = HEx. H (+1) + O (-2) = H22OOHow many +1 would you need to balance the -2 to zero?How many +1 would you need to balance the -2 to zero?Since you need 2 atoms of the 1+ to balance the 2- to zero the resulting compound would be HSince you need 2 atoms of the 1+ to balance the 2- to zero the resulting compound would be H 22OO

In other words: to combine H with O, you MUST have 2 H to balance the oxidation numbers to zeroIn other words: to combine H with O, you MUST have 2 H to balance the oxidation numbers to zero2+ and 2- = ZERO2+ and 2- = ZERO

Ex. Al (+3) + S (-2) = AlEx. Al (+3) + S (-2) = Al22SS33

This one is tricky…we are not even close to balancing + and - to zero.This one is tricky…we are not even close to balancing + and - to zero.

Because of this we must have more than one Al and more than one S in our final equation.Because of this we must have more than one Al and more than one S in our final equation.By using 2 Aluminums instead of just1 we would have 6+By using 2 Aluminums instead of just1 we would have 6+By using 3 sulfers instead of just 1 we would have 6-By using 3 sulfers instead of just 1 we would have 6-Since these are now equal to zero, we combine 2 Aluminums and 3 Sulfers to make AlSince these are now equal to zero, we combine 2 Aluminums and 3 Sulfers to make Al 22SS33

Chemical vs. Physical Chemical vs. Physical ChangeChange

– Physical ChangePhysical Change: A change that can : A change that can occur without changing the identity of occur without changing the identity of the substance.the substance.

– Ex. Solid, Liquid, Gas (Phase change)Ex. Solid, Liquid, Gas (Phase change)

– Chemical ChangeChemical Change: Process by which a : Process by which a substance becomes a new and different substance becomes a new and different substancesubstance

– Ex. FireEx. Fire

Chemical ReactionsChemical Reactions

Chemical Reaction:Chemical Reaction: a process in a process in which the physical which the physical andand chemical chemical properties of the original substance properties of the original substance changechange as new substances with as new substances with different physical and chemical different physical and chemical properties are formedproperties are formed

Chemical Reaction BasicsChemical Reaction Basics

H2 + O2 --> H2O

Reactants- substance that enters into a reaction

Products- substance that is produced by a chemical reaction

Reactants Products

Evidence of Chemical Evidence of Chemical ChangeChange

EPOCH is an acronym that stands for evidence EPOCH is an acronym that stands for evidence that a chemical reaction has occurred.that a chemical reaction has occurred.

– – Effervescence (bubbles and/or gives off gas)Effervescence (bubbles and/or gives off gas) – – Precipitate (solid crystals form)Precipitate (solid crystals form) – – Odor (change of smell is detected)Odor (change of smell is detected) – – Color changeColor change – – Heat (reaction either heats up or cools Heat (reaction either heats up or cools

down)down)

Does sighting evidence of a chemical reaction mean that a Does sighting evidence of a chemical reaction mean that a chemical reaction has undoubtedly taken place?chemical reaction has undoubtedly taken place?

EE

PPOO

CCHH

Types of ReactionsTypes of ReactionsRomance Chemistry :)Romance Chemistry :)

Synthesis-Synthesis- Marriage/Dating Marriage/Dating

A + B = ABA + B = AB

Decomposition-Decomposition- Divorce/Breakup Divorce/Breakup

AB= A + BAB= A + B

Single-Replacement-Single-Replacement- Dance Cut In Dance Cut In

A + BC = AC + BA + BC = AC + B

Double-Replacement- Double-Replacement- Dancing couples Dancing couples switch partners.switch partners.

AB + CD = AC + BDAB + CD = AC + BD

Cartoon ChemistryCartoon Chemistry

This is an example of synthesis

Cartoon ChemistryCartoon Chemistry

This is an example of a decomposition

Cartoon ChemistryCartoon Chemistry

This is an example of a single replacement

Cartoon ChemistryCartoon Chemistry

This is an example of a double replacement

Reaction Types Review…Reaction Types Review…

Match each chemical reaction with Match each chemical reaction with one of the reaction types on your one of the reaction types on your chemical cartoons. chemical cartoons. – Zn + 2HCl Zn + 2HCl H H22 + ZnCl + ZnCl22– NN22 + 3H + 3H22 2NH 2NH33

– 2KI + Pb(NO2KI + Pb(NO33))22 2KNO 2KNO33 + PbI + PbI22

– 2MgCl 2MgCl Mg Mg22 + Cl + Cl22

Conservation of MassConservation of Mass

Atoms cannot be created or Atoms cannot be created or destroyed in a chemical reaction.destroyed in a chemical reaction.

What goes in must come out.What goes in must come out. So we must balance equations to So we must balance equations to

conserve mass.conserve mass.

Balancing EquationsBalancing Equations

Rules:Rules:– We can not add or subtract We can not add or subtract subscriptssubscripts from from

either side of the equationeither side of the equation– We can only add We can only add coefficientscoefficients to the front of to the front of

each compoundeach compound Ex. Ex. 22HH22 + + OO22 --> --> 22HH22OO

H = 4 H = 4H = 4 H = 4 O=2 O = 2O=2 O = 2

Before must match AfterBefore must match After

See “Balancing Act” worksheet for more examples…See “Balancing Act” worksheet for more examples…

Solution ChemistrySolution Chemistry

MixturesMixtures: Matter that consists of two or more substances : Matter that consists of two or more substances mixed but not chemically combinedmixed but not chemically combined

SolutionsSolutions: Homogeneous Mixture in which one : Homogeneous Mixture in which one substance is dissolved into anothersubstance is dissolved into another

Solute = Substance that gets dissolved (ex. Kool-Aid Solute = Substance that gets dissolved (ex. Kool-Aid powder)powder)

Solvent = Substance that does the dissolving (ex. Solvent = Substance that does the dissolving (ex. Water)Water)

AcidAcid: Compound with a pH below 7 that tastes sour and : Compound with a pH below 7 that tastes sour and is a proton donor.is a proton donor.

Ex. Citrus foods Ex. Citrus foods BaseBase: Compound with a pH above 7 that tastes bitter and : Compound with a pH above 7 that tastes bitter and

is a proton acceptoris a proton acceptor Ex. Cleaning Products (soap)Ex. Cleaning Products (soap)

Acids and BasesAcids and Bases

- Solutions can be acidic or basicSolutions can be acidic or basic

- Acids and Bases have unique properties when Acids and Bases have unique properties when dissolved in waterdissolved in water- Acids = sour tasteAcids = sour taste- Bases = bitter tasteBases = bitter taste

- IndicatorsIndicators are substances that change color when are substances that change color when mixed with a solution, which helps to determine if a mixed with a solution, which helps to determine if a substance is an acid or a base. (pH paper, Litmus substance is an acid or a base. (pH paper, Litmus paper, cabbage juice)paper, cabbage juice)

AcidsAcids

Proton donors (H+)Proton donors (H+) Acids contain hydrogen and produce Acids contain hydrogen and produce

positive ions (H+) when dissolved in waterpositive ions (H+) when dissolved in water Acids = good electrolytesAcids = good electrolytes Examples of acids:Examples of acids:

– Lemon JuiceLemon Juice– Citric AcidCitric Acid– Carbonic AcidCarbonic Acid– HClHCl

BasesBases

Proton acceptorsProton acceptors Bases contain hydroxide ions (OH-) Bases contain hydroxide ions (OH-)

when mixed with water.when mixed with water. Bases = weak electrolytesBases = weak electrolytes Examples of bases:Examples of bases:

– AmmoniaAmmonia– SoapSoap– Bleach (chlorine)Bleach (chlorine)

Combining Acids and BasesCombining Acids and Bases

-Mixing acids and bases is a balancing act.-Mixing acids and bases is a balancing act.

(like a teeter-totter)(like a teeter-totter)

Acid + Base = neutral (water and salt)Acid + Base = neutral (water and salt)

Combining Acids and BasesCombining Acids and Bases

EXAMPLE:EXAMPLE:

Acid + Base = neutral (water and salt)Acid + Base = neutral (water and salt)

H+H+ + + OH-OH- HOH + Salt HOH + Salt

Acid Base waterAcid Base water

Ex. Ex. HHCl + NaCl + NaOHOH H H22O + O + NaClNaCl

Measuring Acids and BasesMeasuring Acids and Bases

pH scale- used to measure the pH scale- used to measure the acidity of a solution.acidity of a solution.

Measure pH with indicatorsMeasure pH with indicators pH scale goes from 0 – 14pH scale goes from 0 – 14 0 = very acidic0 = very acidic 14 = very basic14 = very basic 7 = neutral7 = neutral

Acids and BasesAcids and Bases