class07 chemistryg12 notes and homework

8/4/2019 Class07 ChemistryG12 Notes and Homework

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GRADE12CHEMISTRY

OLYMPIADSCHOOL

. .

FRIDAY4.456.45


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Reviewof1st halfofGrade12Chemistry


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Organic chemistry is the study of compounds thatare based on CARBON.

ar on atoms can orm strong s ng e,double, or triple bonds with other carbon atoms.

e ree- mens ona s ape o a mo ecu e s

particularly important when the molecule containsolar covalent bonds. A polar covalent bond is a covalent bond between

two atoms with different electronegativities.

Electronegativity is a measure of how strongly anatom attracts electrons in a chemical bond. The

more strongly to the atom with the higher

electronegativity. This atom has a partial negative,charge. Thus, every polar bond has a bonddi ole: a artial ne ative char e and a artial

positive charge, separated by the length of thebond.


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The figure illustrates the polarity of a doublecarbon-oxygen bond. Oxygen has a higher

electronegativity than carbon. Therefore, theoxygen atom in a carbon-oxygen bond has apartial negative charge, and the carbon atom has a

partial positive charge.

To determine molecular polarity, you must considerthe shape of the molecule and the bond dipolesw n e mo ecu e.

If equal bond dipoles act in opposite directions inree- mens ona space, ey coun erac eacother. A molecule with identical polar bonds that

.


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Hydrocarbons are the simplest type of

or anic com ound. The are com osedentirely of carbon and hydrogen atoms,

.

they contain only carbon and hydrogen

, -

compounds.


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An alkane is a hydrocarbon that has only single bonds. Alkanesthat do not contain rings have the formula CnH2n+ 2. An

alkane in the shape of a ring is called a cycloalkane.Cycloalkanes have the formula CnH2n.

n a ene s a compoun a as a eas one ou e on .Straight-chain alkenes with one double bond have the same

, .

* A double bond involves two pairs of electrons. In a doublebond one air of electrons forms a sin le bond and the other

pair forms an additional, weaker bond. The electrons in theadditional, weaker bond react faster than the electrons in thesingle bond. Thus, carbon-carbon double bonds are morereactive than carbon-carbon single bonds.

n a yne s a compoun a as a eas one r p e on .straight chain alkyne with one triple bond has the formula

- .

bonds. The functional group for an alkyne is the triple bond.


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A functional group is a reactive group ofbonded atoms that appears in all the members

o a c em ca am y. ac unct ona groupreacts in a characteristic way. Thus, functional

chemical properties of compounds. yorganic compounds is R+ functional group.

.more than one alkyl group is present, R2and

.

.often have similar physical properties.

.react chemically in very similar ways.


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Alcohols, alkyl halides, ethers, and amines allhave functional rou s with sin le bonds.

An alcohol is an organic compound that.

on the position of the hydroxyl group, an alcoholcan be primary, secondary, or tertiary.


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An alkyl halide (also known as a haloalkane) is analkane in which one or more hydrogen atoms have been

, , , , .functional group of alkyl halides is RX, where Xrepresents a halogen atom. Alkyl halides are similar instructure, po ar ty, an react v ty to a co o s.

An ether is an organic compound that has two alkyl.of an ether is ROR. You can think of alcohols and ethersas derivatives of the water molecule.

Aldehydes and ketones both have the carbonylfunctional group. An aldehyde is an organic compound-

carbon chain. The general formula is RCOH. A ketone is

an organic compound that has a double-bonded oxygenon any carbon within the carbon chain. The generalformula for a ketone is RCOR2, where R and R2 are

.


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A carboxylic acid is an organic compound with the carboxyl. .

An ester is an organic compound that has the generalformula RCOOR2, where R is a hydrogen atom or ay rocar on, an s a y rocar on. ou can n o an

ester as the product of a reaction between a carboxylic acid

and an alcohol._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

enzene s a cyc c compoun w t t e equ va ent o t reedouble bonds and three single bonds However, the electronsthat form the double bonds in benzene are s read out andshared over the whole molecule. Thus, benzene actually hassix identical bonds, each one half-way between a single anda double bond. These bonds are much more stable thanordinary double bonds and do not react in the same way.Molecules with this type of special electron sharing are called

.


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There are 3 main types of Organic

Reactions: Addition reactions;

u st tut on react ons; an Elimination reactions

* Most organic reactions can be classified

y .


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In a substitution reaction, a hydrogen atom or afunctional rou is re laced b a different

functional group. Twocompounds usually reactto form twodifferent roducts. The or anicreactant(s) and the organic product(s) have the

Alcohols, alkyl halides, and aromatic

reactions.


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In an elimination reaction, atoms are removed froma molecule to form a double bond. This type of

v .reactant usually breaks up to give twoproducts.

bonded to carbon atoms than the organic reactant

did. Alcohols often undergo elimination reactions when

they are heated in the presence of strong acids,

such as sulfuric acid, H2SO4, which acts as acatalyst. Alkyl halides also undergo elimination.


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REDOX: Oxidation and reduction always occur together.One reactant is oxidized while the other reactant isreduced. In or anic chemistr oxidation and reduction

are defined by the changes of the bonds to carbonatoms in the organic reactant.

atom forms more bonds to oxygen, O, or less bonds to

hydrogen, H. Oxidation occurs when an organic.oxidizing agents include acidified potassiumpermanganate, KMnO4, acidified potassium dichromate,

, , .

symbolize an oxidizing agent. Reduction is defined as a reaction in which a carbon

, ,hydrogen, H. Often, a CO bond or CC bond is reduced

to a single bond by reduction. Reduction occurs when ano ga c co pou eac s w a e uc g age .Common reducing agents are lithium aluminum hydride,LiAlH4, and hydrogen gas over a platinum catalyst,

. e sym o s use o sym o ze a re uc ngagent.


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Atoms,ElectronsandPeriodicTrends

Rutherford: the atom is made up mainly ofem t s ace, with a small, massive re ion ofconcentrated charge at the centre. the

nuclear model of the atom The problem: Atomic Spectra - The visible

ortion of the electroma netic s ectrum is a

continuous spectrum. According to nineteenthcentury physics, part of the energy emitted byelectrons should be observable as a continuous

spectrum. This is not the case. Instead, whena oms a sor energy, you o serve a pa ern odiscrete (distinct), coloured lines separated by

.


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Bohr was able to explain the line spectrum forh dro en because his idea incor orated several

new eas a out energy. Bohrs model: Pictures electrons in orbit around a

cen ra nuc eus. n e u er or s mo e , n

which electrons may move anywhere within the,imposes restrictions.


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Planck suggested that matter, at the atomic level,

energy. Each of these specific quantities is called a.

an atom is quantized.

.occurs as quanta of electromagnetic energy that

- . -packets of energy were later called photons. In

,energy) travels in the form of photons of energy.

lines in this spectrum corresponds to the change in

lower energy levels.


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When a hydrogen atom is exposed to electrical current, or to another form ofelectromagnetic energy, its electron absorbs photons of energy. It is now inan excitedstate.

,

higher energy level. When the electron falls to a lower energy level, it emitslight of certain energy. A line spectrum results when atoms in an excited state emitphotons as they

a o a ower energy eve . s s an em ss on spec rum.


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Another kind of spectrum that is related to an atoms emissions ectrum is an absor tion s ectrum. This kind of s ectrum

results when electrons of atoms absorb photons of certainwavelengths, and so are excited from lower energy levels to

.


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Schrdinger introduced the concept of quantum-

equations to describe the wave properties of sub-microscopic particles such as electrons, atoms, and.

mechanics to propose a new atomic model.

The quantum mechanical model of the atom: This modelenergy because of the wave-like properties of theirelectrons. The figure depicts the volume surrounding the

-because of a scientific principle called the uncertaintyprinciple.


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HeisenbergUncertaintyPrinciple:If you can know anelectrons precise position and path around the

nucleus, as you would by defining its orbit, youcannot know with certainty its velocity. Similarly, ifyou know its precise velocity, you cannot know

with certainty its position. Based on the uncertaintypr nc p e, o rs atom c mo e s awe ecauseyou cannot assign fixed paths (orbits) to the motion

o e ec rons. Schrdinger used a type of equation called a waveequation to define the probability of finding an

atoms electrons at a particular point within theatom. ere are many so ut ons to t s waveequation, and each solution represents a particularwave unc on.


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Each wave function gives information about an

.

Chemists call these wave functions ORBITALS.

r ta s ave a var ety o erent poss e

shapes. Therefore, scientists use four quantumnumbers to describe an atomic orbital. One

, ,

energy level and size. A second quantum, , .

quantum number, ml, describes an orbitalsor entat on n space. ourt quantum num er,

the spin quantum number, ms, describes the

spin of an electron.


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P li E l i P i i l O l t l t f it i


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PaulisExclusionPrinciple:Only two electrons of opposite spin

can occupy an orbital OR No two electrons in an atom have

the same four quantum numbers OR Each electron in anatom has its own unique set of four quantum numbers.


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MorefromAtoms,Electronsand

PeriodicTrends

HistoricalEvents,OrbitalFilling;Trendsinthe

PeriodicTable;thes, ,dandfblocks;etc...


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Structures and Properties of Substances

Chemical bonds are electrostatic forces that

hold atoms together in compounds.

involves energy. Lower-energy systems tend to

-

systems. Bonded atoms, therefore, tend to,

atoms.

valence electrons

Ionic Bonding: The force of attraction between


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Ionic Bonding: The force of attraction betweeno ositel char ed ions cations + and anions

{-}, constitute an ionic bond. Ionic bondingoccurs between atoms of elements that havelarge differences in electronegativity usually

-metal with high electronegativity.

,

properties:,

Hard but brittle

on-con uc ors o e ec r c y an ea

High melting points

Many ionic solids are also soluble in water.


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CovalentBonding:Covalentbondsareforcesofattractionformed.

abalancebetweentheforcesofattraction andrepulsionthatact

betweenthenucleiandelectronsoftwoor moreatoms.

Thequantummechanicalmodelcanbeextendedtoexplainbonding.A covalentbondmayformwhentwohalffilledatomicorbitals from

.bondinvolves theformationofaneworbital,causedbytheoverlappingofatomic orbitals.Theneworbitalhasenergylevelsthatarelowerthanthoseof theoriginalatomicorbitals.

Bond energy (E) is a measure of bond


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Bond energy (E) is a measure of bondstren th in a chemical bond. It is the heat

required to break Avogadro's number ofmolecules into their individual atoms. Bondenergy is the energy required to break the force

to separate them. Thus, bond energy is a.

To predict an ionic versus covalent bond,

electronegativity difference is characteristic of

.describe the formation of ionic compounds in

atom to another.

Chemists consider bonded


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Chemists consider bondedatoms with a difference in EN

.mostlycovalent; electrons areshared equally or nearly

. For bonded atoms that have a

difference in ENbetween 0.4. ,polar covalent. A polar covalentbond is a covalent bond with

electrons between two atoms. This unequal sharing results in

positive and partially negativepoles. Bonded atoms with a

difference in ENbetween 1.7and 3.3 are mostlyionic;electrons are shared sounequally that one bondeda om as a s rong nega ve

charge and the other has astrong positive charge.


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ofSubstances(ChemicalBondin )

,

Bonding,ResonanceStructures,VSEPR,

, ,

etc...


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Energy and Change (Studying

Energy Changes) e aw o conserva on o energy s a es a e

total energy of the universe is constant. In other,

created. This idea can be expressed by thefollowin e uation: Euniverse = 0

Universe=

System+

SurroundingsEuniverse = Esystem + Esurroundings = 0

=

Heat, Q, refers to the transfer of kinetic energy.

a measure of the average kinetic energy of theparticles that make up a substance or system.

* Temperature in Kelvin degrees=

Temperature inCelsius degrees + 273.15

Ch i t d fi th


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Chemists define thetotal internal energy of

a su s ance a aconstant pressure asits enthalpy, H.

enthalpy change, H,

that accompanies aenthalpy of thereactants and products

In chemical reactions,enthalpy changes

bonds being brokenand formed. Chemical

bonds are sources ofstored energy.Breaking a bond is aprocess that requiresenergy. rea ng a

bond is a process thatreleases energy.


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f d h


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MorefromEnergyandChange

(StudyingEnergyChanges)

HeatCapacity,SpecificHeatCapacity

= , ,

Summation,CalculatingEnthalpyChanges


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class07 chemistryg12 notes and homework

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