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The Nature of MatterMatter: all substances and materials in the universe. They each have volume (occupy space) and mass.Whichever chemical substance we study, it can exist in three different physical states.All matter is made up of particles called atoms / molecules

MatterMatterSolidLiquidGasSolid, Liquid, Gas

Solid

Properties:Has a fixed volumeHas high densityHas a definite shapeDoes not flow

Particles arrangement:Packed closely togetherHave orderly arrangementLittle empty spacesStrong forces between particlesParticles can vibrate but not moved from their fixed positionLiquid

Properties:Has a fixed volumeModerate to high densityTakes the shape of the containerGenerally flow easily

Particles arrangement:Packed closely together (< solid)Not in orderly arrangementLittle empty spaces (> solid)Strong forces between particles (< solid)Particles can vibrate & moveGas

Properties:No fixed volumeLow densityNo definite shapeFlow easily

Particles arrangement:Particles are far apartRandom arrangementA lot of empty spacesNo forces between particlesParticles can vibrate & moveChanges in Physical StateGasLiquidSolidCondensation / liquifactionMeltingEvaporation / vaporisationFreezing / solidificationSublimationIncreasing temperatureMelting point: the temperature at which a pure substance turns from solid to a liquid.Freezing point: the temperature at which a pure substance turns from liquid to solid.Melting & FreezingSolid gas or gas solidEg. Carbon dioxide (dry ice)IodineCamphor

SublimationEvaporation and condensation take place over a range of temperature.Eg. Splashes of water evaporates at room temperature.Water vapour turn to form dew in the morningThe larger the surface area, faster evaporation.Boiling takes place at specific temperature (Boiling point / BP). BP depends on the surrounding pressurePressure increase BP increase, vice versaEg. Pressure cookerVolatile liquid low boiling pointBP decrease volatility increase

Evaporation, Condensation, BoilingThe boiling & melting points depends on the purity of substances pure substance melts & boils at definite temperature. We can use this to test purity of substances.Impure substance melts / boils over a range of temperatures, not a particular point. Lowers the melting pointRaises the boiling point

Purity of SubstancesShow the change of temperature over time.During the change of phase, the temperature stays constant.Solid to liquid and liquid to gas heat energy is taken inGas to liquid and liquid to solid heat energy is released Impure substances melt over a range of temperatures (eg. Wax). Heating & Cooling CurvesHeating curve of water

Mixture: made from at least two parts. Solutions: Combination of substances in different states. Soluble solids can dissolve in a liquid solvent.Solute: solid that dissolves in liquidSolvent: liquid in which the solid dissolvesInsoluble solids do not dissolve but they form suspensions in liquid.Alloy: mixture of metals.Liquids can be miscible / immiscible.Types of MixtureTypes of MixtureMixtureInsoluble solid + liquidSoluble solid + liquidTwo / more miscible liquidsMixture of small amounts of solidsImmiscible liquidsSeparation TechniquesSeparation method depends on:Type of mixtureWhich substance in the mixture that we are most interested in.

SeparationMixtureInsoluble solid + liquidSoluble solid + liquidTwo / more miscible liquidsMixture of small amounts of solidsDecantationDistillationObtain liquidCrystallisationObtain solidDistillation / fractional distillationChromatographyImmiscible liquidsDecantationCentrifugationFiltrationSeparation TechniquesSeparating insoluble solids from liquidsResidue: insoluble materialFiltrate: liquid phaseFiltration

Separating insoluble solids from liquids if the solids are large enough.Separating immiscible liquids based on different density of the liquids.Decantation

Separating funnelSeparating insoluble solids from liquidThe mixture is spun at high speed in a centrifuge. The solid deposited at the bottom of the tube and the liquid can be carefully decanted off.CentrifugationBased on different densitySome solids will float and others sink.Eg. Collecting gold dust in the river sediment, purifying ores of zinc / copper. Based on different solubilitySome solids will dissolve and others are notBased on magnetic propertiesMagnetic solids can be separated first using magnet. Separating Mixtures of SolidsBased on magnetic properties

Separating Mixtures of Solids

Separating dissolved solids from liquid.

Crystallisation

Separating mixtures of liquidsBased of different boiling pointsLiquid with lowest boiling point distilled first.

Distillation / Fractional Distillation

Separating mixtures of dissolved solid with different solubility.Pure substance will only have 1 spot.This method can tell whether a solution has become contaminated.

Rf =

Chromatography

Distance moved by the substanceDistance moved by the solvent frontFor separating non-coloured substances, locating agent is required to produce coloured spots.Test of purity: Paper chromatography pure substance only have 1 spot. The identity of sample can be checked by comparing the Rf value to the sample known to be pure. Melting & boiling point test. Identity can be checked against the measured value for known substances.

Purity & Identity of Substances

Purity is of crucial importance. Eg.Medicinal drugs (pharmaceuticals) contaminating substances may have harmful side-effects.Food colouring need to be controlled as some may cause problems (asthma, allergies).Purity is often presented as % % Purity =PurityMass of pure substanceTotal mass of impure substanceSolubilityIf a substance dissolves in a solvent, it is called soluble. Otherwise, it is called insoluble. More substance dissolves more concentrated solution.The concentration of the solution is the mass of solute dissolved in a particular volume of solvent (usually: g/L)

SolubilityIf we keep adding more solid, a point is reached where no more solids can dissolve at that temperature called: saturated solutionTo get more solids dissolve increase T.Unlike solids, gases will become less soluble as T rises. Solubility : mass of solute that will saturate 100 grams of water at particular T.

SolubilitySolubility curves: curves showing how the solubility of a substance changes with temperature.When saturated solution is cooled some solids crystallises out since the solvent can hold less solute.The solubility of gases in liquids affect the gas used by a deep-sea diver (read p. 42).

Solubility CurvesAtoms & MoleculesAtoms & MoleculesMATTERPure substances:Only one substanceNo impuritiesMixtures:More than 1 substanceMay be in different statesElements:Cannot be divided into simpler substancesCompounds:Made from 2 / more elements chemically bonded togetherA substance that cannot be broken down into simpler substances by ordinary chemical methods.There are 94 elements found naturally, but 8 of them account for more than 98% of mass of the Earths crust. Silicon & oxygen (bound together in silicate rocks) make up three-quarters of the Earths crust. Only certain elements are able to form complex compounds found in living things.Human body contains 65% oxygen, 18% carbon, 10% hydrogen, 3% nitrogen, 2% calcium, 2% other elements.The smallest particle of any element is called atom.ElementsElements are classified as metals and non-metals

ElementsMetalNon-metalGood electrical conductorsDo not conduct electricityShiny DullStrong and hard (in mixtures called alloys)Weak and softCan be bent (malleable) and stretched (ductile)Brittle and break easily when bent or stretchedGood heat conductorsPoor heat conductorsHigh densityLower densityHigh melting and boiling pointsLow melting and boiling pointsCompound: a substance containing two or more elements joined together by chemical bonds.Eg. Water, magnesium oxide Mixture: a combination of two or more substances without chemical bonds between the substances. No chemical reaction takes place in the formationEg. Mixture of salt and water

Compounds & MixturesCompounds & MixturesHydrogenOxygenMixture of hydrogen & oxygenMixture of hydrogen & oxygen+WaterChemicalreactionEach circle represents an atomPairs of atoms are called moleculesCompoundMixtureCompositionFixed composition by massVariable composition by massMelting and boiling pointsFixed MP and BPVariable MP and BPPropertiesPhysical and chemical properties different from its elementsHas same properties as its componentsSeparationCannot be separated by physical means need chemical reactionCan easily be separated by physical methodsArrangement of atomsCompounds vs Mixtures

Chemical reactions: Decomposition: where a compound breaks down to form two or more substances.Eg. Copper(II) carbonateCopper oxide + CO2 Synthesis: combination of two or more substancesEg.Magnesium + Oxygen Magnesium oxideChemical ReactionsHeatHeatChemical reactions:New chemical substance(s) are formed.Usually the process is not easily reversed.Energy is often given out.

Physical change (eg. melting / dissolving):The substance do not change identity.They can be easily returned to their original form by some physical process.Chemical ReactionsKinetic theory:All matter is made up of very small particles:Different substances contain different types of particles, such as atoms or moleculesThe particles are moving all the timeHigher temperature higher average energy of particles.The freedom of movement and the arrangement of the particles is different for the three states of matter.Kinetic Theory of MatterParticles spreading to fill the space available to the molecules.Diffusion involves movement of particles from higher concentration to lower concentration region, until the particles are evenly spread. Diffusion in liquid is much slower than in gases.Diffusion does not take place in solids.

Diffusion

Not all gases diffuse at the same rate.The speed of gas atoms or molecules are high, but they are slowed down by other particles in the air.

Diffusion of Gases

Heavier particles move slower than lighter particles at same temperature.Larger molecules diffuse slower than smaller ones.The pressure of a gas is the result of collisions of fast-moving particles with the walls of the containerAverage speed of the particles increases with increasing temperature.DiffusionAbsolute scale of temperature is based on the behaviour of gas.A graph of volume of gas vs T will give a straight line, which shows that the volume is proportional to the temperature. It was found that the volume of the gas reaches 0 at -273C.A graph of pressure vs T also show similar straight line.It was found that the pressure is 0 at -273C.Gas pressure is produced from particles collision with the container walls, hence it can be concluded that at this temperature, gas particles are not moving.This temperature is known as absolute zero and the scale is named after Lord Kelvin, which starts at 0K. Absolute Scale of TemperatureThe Structure of the AtomDaltons theory:A pure element is composed of atoms.The atoms of each element are different in size and mass.Atoms are the smallest particles that take part in a chemical reaction.Atoms of different elements can combine to make molecules of a compound.Each element has its own symbol and they can be combined to show the formulae of complex compounds. Atomic TheoryAll atoms consisted of three subatomic particles protons, neutrons, and electrons.A single atom is so small and the mass can only be compared with another, using mass spectrometer. The element carbon is chosen as the standard. This gives relative atomic mass.Carbon is given a relative atomic mass of 12. Hydrogen is the lightest atoms of all. Calcium (atomic mass of 40) is 40 times as heavy as Hydrogen.

Atomic StructureNucleus is made of protons and neutrons. Protons and neutrons have almost the same mass. Electrons have virtually no mass.Protons and electrons have equal opposite electric charge, while neutrons are electrically neutral.Identity of an element is determine from its proton number.Subatomic Particles+NN+--protonelectronneutronShellProton & Nucleon NumberHethe number of protons and neutrons in an atom4Nucleon number (Atomic mass)the number of protons in an atom2proton number (atomic number) number of electrons = number of protonsNumber of neutron = nucleon number proton numberIsotopes are atoms of same elements with different mass number.Same number of protons and electrons, but different numbers of neutrons in the nucleus.They have the same chemical properties, but some physical properties are different. Some isotopes have unstable nuclei; they are radio-isotopes and can emit various forms of radiation. IsotopesIt is the average mass of an atom of an element taking into account of its natural isotopes and their percentage abundance.Eg. Chlorine contains 2 isotopes Cl-35 and Cl-37 in a ratio of 3:1 (75%:25%).

= 35.5

Ar can be found from periodic table.

Relative Atomic Mass (Ar)

Radioactive isotopes are widely used in industry and medicine. Examples:Uranium-235 in nuclear power stations.Detecting level of liquid in a container.Checking thickness of sheets of plastic, paper, or metal foilDetecting leaks in gas or oil pipesFor medicine: kill biological cells that are sensitive to radioactive emissions.Sterilising medical instruments.Industrial Application of Radio-IsotopesSome isotopes are unstable. The extra neutrons cause them to disintegrate or decay spontaneously. Each radio-isotope decays at its own rate. It is a completely random process, unaffected by temperature or whether it is part of a compound / free element. nuclear process, not chemical reaction.

RadioactivityThe time taken for the radioactivity in a sample to halve is constant for a particular radio-isotope. Half-lifeThis can be used to date wooden and organic objects, age of rocks. RadioactivityElectron ArrangementsNatural light display in the sky. Collision of energetic charged particles with atoms in the high altitude atmosphere.

Bohrs theory:Electrons are in orbit around the central nucleus of the atomElectron orbits are called shells (or energy levels) and have different energies.Shells further from the nucleus have higher energiesThe shells are filled starting with the one with lowest energy.

Electrons Arrangements in an Atomsn =1 2 e-n =2 8 e-n =3 18 e-For atoms in the main-group (group I VIII / 0)The number of electrons in the outer shell is equal to the group number.The number of shells is equal to the period number.You can predict the position or identity of an unknown atom given the number of the electron.Eg. Atom X has 15 electrons. What is your prediction of atom X?Electron configuration = 2, 8, 5 group V, period 3So the atom X is P.

Electron Arrangement in an AtomsThere are three different physical states and the changes can be made by changing T and/or P. Pure substance have precise MP and BP. Impurity changes BP and MP.Range of separation methods.Difference of elements and compoundsThe kinetic theory of an atom.Diffusion in liquid & gasesSummaryAtomic structure Subatomic particlesIsotopes and radio-isotopesElectron arrangement

Summary