How small is an atom?• A grain of sand contains ~125 million trillionatomsIf the atoms were each the size of a baseball, wecould cover the state of California to a height ofabout 39,000 feet – That’s where Jumbo Jetsfly!
How Small?!?• A cell can contain on the order of 100 Trillion Atoms.Height of baseballs in California: one layer of baseballsacross the whole state.Red blood, platelet and white blood cellsphoto from public domain100 Trillion atoms?But we need a microscopejust to see these!
Properties of Substances• Physical Properties- Tells us about the stuff itself, without it being turnedinto a new substance.(Example: water is a liquid at room temperature.)• Chemical Properties- Tells us what it can change into, and under whatconditions.(Example: water can be split into hydrogen and oxygen gas ifyou run an electric current through it.)
Classify the following as eitherchemical or physical properties:• Is green• Has density 2.1 grams/cm3• Will ignite at 451 degrees Fahrenheit• Boils at 100 degrees Celsius• unstable (as in explodes when dropped)• Is 6 feet tall• Will explode when it contacts water• Will dissolve in water (such as dissolving sugar into water)PhysicalPhysicalChemicalPhysicalChemicalPhysicalChemicalPhysical*
How we describe changes in stuff:Physical and Chemical Changes• Physical change– change in size, shape, etc., but molecules remainthe same.• Chemical change– new stuff gets made.
• Ask yourself the question: If I changed thephysical conditions (temperature for instance)back to what they were before the change,would it undo the change?If so, you have a physical change.If not, you have a chemical change.
Classify the following as eitherchemical or physical changes:• It is burning• It is melting• It is evaporating• It is turning brown in the presence of air• It is forming bubbles when I add it to water• It is boiling• It is rustingChemicalPhysicalPhysicalChemicalChemicalPhysicalChemical
Example Test Problem_____1a) Will ignite at 451 Fahrenheit._____1b) Has density 2.1 g/cm3_____1c) Can be made into thin sheets_____1d) melts at 50 ºC_____1e) it is evaporating_____1f) it is rustingCPPPPC
Chemical formula• Represent what atoms in acompound• Uses abbreviation fromperiodic table to representeach type of atom• Subscripts following tell howmany of that type of atom(one is implied, so H2O =H2O1).O2CH4H2OCO2
Nomenclature: how stuff gets named1) Special Cases (of which there are many):Water (H2O)Ammonia (NH3)Methane (CH4)2) Compound on the left + Compound on the right + ‘ide’NaCl – Sodium ChlorideLi2O – Lithium OxideCaF2 – Calcium Fluoride
Nomenclature 23) Number prefix + Left compound + Number prefix + Right compound +‘ide’CO – Carbon MonoxideCO2 – Carbon DioxideWater could be called ‘dihydrogen monoxide’ but what a mouthful it would be.Possible number prefixes:1 – mono2 – di3 – tri4 - tetra
Name the Following:MgCl2KClH2OCONH3BF3Magnesium ChloridePotassium ChlorideDihydrogen monoxideCarbon MonoxideNitrogen Tri hydrideBoron Trifluoride
Wrapping Up:• Physical properties – detail what something is like– Physical changes can be reversed by altering physical conditions• Chemical properties – detail how something reacts– Chemical changes result in a new material• Chemical formulas use symbols from the periodic table to tellyou how many of each type of atom are in a material.• Naming:– Sometimes a material has a common name– Most of the time we use a long-form name such as “Carbon Di-Oxide”for CO2
Most materials are mixtures:• Air: Nitrogen (N2), Oxygen (O2), minor amounts ofother gasses• Steel: Iron (Fe), Chromium (Cr), Nickel (Ni), Carbon(C)• Seltzer: Water (H2O) and Carbon Dioxide (CO2)In fact, tap water is a mixture – it contains many things,typically around here carbonates (we have ‘hard’water in this region).
• Mixtures do not react when formed - when youmix salt into water the salt stays salt (NaCl)and the water stays water (H2O).• Mixtures may be separated by physical means:– Solids separated from liquids by filtration– liquids from other liquids by distillation
Purity• “Pure” materials contain one element orcompound – pure gold, pure water.• True purity is never found – even a spec ofsomething else prevents 100% purity.• Purity is relative. 99% pure gold is less purethan 99.9% pure gold.
So we break down matter like this:MATTERASK: Can it be separated by some physical method?YES NOMixture SubstanceYES NOASK: Can it now be separated by someother method?Substance contains morethan one atomCompoundSubstance contains only onekind of atom, has no bondsElement
Table of organization of matter:Macroscopic MicroscopicMixtureSubstanceCompoundElementPotentially multiple‘things’ in itA single material, all ofsame typeA substance made ofmore than one type ofatomA substance made ofone type of atomMay or may not bedistinguished as twoor more ‘things’Appears uniformAppears UniformAppears UniformHeterogeneous mixtures appear to be two different things to our eye.Homogenous mixtures appear to be a single thing to our eye.
Substances:Elements and Compounds• Consider a pure substance.“Pure” refers to a substancewhich, from a MACROscopicview appears:• Suppose that you try to dosomething to break it into two ormore different substances.– If we CAN then we say that the originalsubstance was a(n):– If you CAN’T then we say that thesubstance is a(n):uniformCompoundElementCompounds Element
Separation:• (Demo) Mechanical separation, also known as filtration.• Separation by boiling point, also known as distillation.• Centrifuge – a form of mechanical separation by rapid spinning,common for separating the components of blood.
Example ProblemSuppose you are given a container of purpleliquid. How would you determine if the liquid isa mixture, compound or element?(Hint – how could you separate a mixture?)
• What happens when we dissolve something?– Is it lost?– Does it fit into the space between particles in thething it is dissolved into?– Or does something else happen?
• Something else happens. The salt takes up its ownspace.• Salt is pulled away from salt crystals by attraction towater molecules.Demonstration: salt dissolving in water
Solutions• Examples: sugar in water, salt in water, chromium inaluminum oxide (ruby), titanium and iron inaluminum oxide (sapphire).• solvent – larger component• Solute – smaller components• Process of mixing solute into solvent: dissolution ordissolvingDissolving depends on attractions between solvent andsolute.
ConcentrationConcentration means how much stuff is in oursolution. One common way:Grams SoluteLiters SolutionConcentration =
The Mole• The mole is a measureof number of particles– 6.02*1023particles = 1 mole– a couple coconuts = 2 coconuts– a dozen donuts = 12 donutsYou are here:If you stack one mole(6.02*1023) pennies it wouldmake a stack the diameterof the Milky WayMilky Way
Concentration with MolesFor chemists Moles are a more convenientmeasure – they tell you how many moleculesof the solute are in the solution.When measured this way, 1 mole of solute in 1liter of solution is called “1 Molar”Moles SoluteLiters SolutionConcentration =