2Physical Properties = a property that describes the behavior of a substance without reference to another substance.You look at the substance by itself, not combined with anything else.Weight, color, volume, boiling point, melting point, hardness, etc.Chemical property = a property that describes the behavior of a substance when it reacts or combines with another substance.Burn it or add other chemicals to make it react.
3We can measure both physical and chemical properties 2 things may have some properties that are the same, but not all of them will be.We do tests until we get only one substance with all of the properties._______________________________________The Metric SystemScientists have used this system for over a centuryCreated in 1791, it is based on units of 10
4The English system is not based on any unit. It is based on things that change1 foot changed depending on whose foot it wasIt is only used in the USAThe metric system is used by every other country in the worldIn the metric system you can change from one unit to another by just moving the decimal.EX) – 1 meter = 1000ml, 100 cm, 10dm, ,.1dkm, .01hm, .001km
5Nature of MatterMatter = anything that has mass and takes up space.Matter is made of atomsAtoms are the simplest form of any elementElements are only made of one type of atomEverything that is matter is made of two or more of these elementsPeriodic table = a chart of all of the known elements arranged in a systematic fashion
6Vertical columns are called groups or families Things in the same column have similar propertiesEach element has a letter or letters as a symbolMany of the element’s symbols are in LatinEX) Gold = Au = Aurum (Latin for gold)When we combine elements, we get compoundsMost everything on the planet is a compound or is made of compounds
7Carbon dioxide is written as CO2, which means it has one atom of carbon and two atoms of oxygen. Carbon Dioxide is a new substanceCarbon is a solid and Oxygen is a gasCarbon dioxide is a gas that does not act like either of these.States of MatterThere are three states of physical matter – solid, liquid, gas
8SolidsThe molecules in a solid are very tightly packed in a 3-D formThe molecules are moving, but just barely by vibratingThis gives solids a definite shape and a definite volumeLiquidsThe molecules in a liquid move much faster than in a solid.
9They move so fast that the 3-D form breaks down into chains of molecules They have no definite shape, but do have a definite volumeGasesThe molecules are now moving very quicklyThe liquid chains now are moving so fast that they break apart into individual moleculesThe have no definite shape and no definite volume.
10Changing states of matter You can change from one state of matter to another by adding or taking away energy.EX) water – heat the water (liquid) past 100°C and you get water vapor (gas). Remove heat from water (liquid) until you get to O°C and it turns into ice (solid)Through all of this, it is still H2OSometimes a solid can turn directly into a gas.This is called sublimation
11EX) dry ice is solid CO2 and will change into a gas at room temperature without ever turning into a liquid.Scientists are constantly combining compounds and elements in all their phases to try to make new and useful products.Most do not work and some are dangerousWhen there is a definite boundary between two substances it is called a phase- Ex) oil and water
12This is one way forensic scientists can tell what a substance will be. Theory of lightKnowing how light works is important to forensics.There are two theories as to how light works – one is as a wave and the other is as a particleWave theoryThis says light travels in waves, like water
13It has crests (high points) and troughs (low points) Wavelength = the distance between two crests- Its symbol is Lambda (ʎ) and is measured in millionths of meters ( )Frequency = how many times a wave passes a point in a given amount of timeIts symbol is (f)f = c÷ʎ - OR: frequency = the speed of light divided by wavelength
14Visible light (sunlight) is made of many different wavelengths Each wavelength is a different color.When we use a prism, it splits the light into different wavelengths.This is called dispersionThe spectrum of visible light has 7 main colors: red, orange, yellow, green, blue, indigo and violetWhen light goes through something (glass, water, etc) is slows down.
15Depending on what it is, it may slow down a little or a lot The is called RefractionWhen light bounces off something it is called ReflectionEverything you see is reflected light.If a shirt is blue, it is reflecting blue and absorbing the other colors.White reflects all the colors and black absorbs all the colors.
16Light absorption is an important part of forensics. Certain chemicals will absorb and reflect certain colors.The electromagnetic spectrumThis includes every wavelength that comes from the sun.Every wavelength from the sun travels at the speed of light (300 million meters/second)
17This ranges from things that have a high frequency and short wavelength, to low frequency and long wavelengthThe highest frequencies belong to gamma raysThese kill life because they have so much energyX-rays have a slightly lower wavelength-it still has enough energy to push through muscles and bounce off of bone.Given enough dosage, X-rays can cause cancer
18Ultraviolet rays have a frequency that is only a little higher than visible light. Ultra is Latin for “above”This can cause skin cancer.Visible light (what we can see) is a very tiny part of the electromagnetic spectrum.Things that have a lower frequency and longer wavelengths than visible light are infrared (heat), microwaves and radio waves
19Normally, light waves are not in step with each other. - they bump into and interfere with each other.This is why a single light can light up a roomWe have found a way to make the rays stay in step with each other.This creates a light with only one wavelengthThis is a laser = light amplification by stimulated emissions of radiation.
20Light as a particleIn space, light acts like a wave.When it is absorbed by something, it acts like a particlePhoton = energy particles of lightEach photon has a specific amount of energyE = hfE is the energy of the photonh is Plank’s constantf is the frequency of the wave
21In other words, the higher the frequency of light, the more energy the photons will have. EX) – X-rays have higher energy photons than infrared rays do.This is why x-rays cause cancer and infrared rays do not.We can tell what photons of light are absorbed by something by using spectrophotometry.This is very useful when figuring out what kind of drugs are on a scene.
22Refractive IndexWhen light rays change speed, it will bendEX) quarter in a poolLight bounces off the quarter, through the water, and into the airWhen it hits the air, it speeds up a lot, and bendsThis is why, when you try to pick up a quarter in a pool, it is not where you think it is.Refractive index = the velocity of light in a vacuum (space) divided by the velocity of light through something.
23The refractive index for any substance changes based on its temperature and lighting conditions. So in order to do tests, the conditions have to be carefully controlled.Almost all refractive indices use a wavelength of nanometers.This give us a standard for doing the tests.Anything light passes through has a refractive index.If it goes from one gas to another, it changes speed. Same for liquids and solids.
24If you put a solid in a liquid with the same refractive index the solid disappears. In a crystal, there can be two different refractive indices.If you turn the crystal, the refractive index changes.Crystals have a repeating pattern as to how their atoms are arranged that we can use for identification.Glass is not a crystal.Its atoms are arranged in a random fashion.This is how we can tell the difference between glass and crystal.
25Knowing if what you are looking at is a crystal or not will change how you figure out the refractive index.Forensic analysis of glassWe look at the composition of the glass, the glass fragments themselves, the density of the glass, the refractive index, and the glass fractures.Density and refractive index are the two most easily done tests and are the most accurate of the tests.
26Glass CompositionGlass is made of sand mixed with various metal oxides as well as other minerals.Soda (sodium carbonate) is usually mixed with the sand to lower its melting point and make it easier to work with.Lime is added to the mixture to keep it from dissolving in water.This soda-lime glass is used in most windows and glass bottles.
27This mixture is cooled on top of liquid tin. This is called “float glass”.The metal oxides in glass are generally sodium, calcium, magnesium and aluminum.Specialized glass (colored glass) uses other metals.Heat resistant glass uses boron oxide to keep it from shattering from heat. (chemistry beakers)Tempered glass is made by rapidly heating and cooling the glass so it breaks into “dices”
28These are small, cube pieces that break off. This is used in the rear and side windows of cars.Laminated glass is made by putting a layer of plastic between two layers of glass.This makes it very strong and resistant to cracking.This is used in the front windshields of cars.