 Properties must be determined to identify the source of evidence  Physical Property – describes a substance (uses the sense)  Ex: weight, boiling point, ______________________  Chemical Property – describes how a substance reacts with other substances  Ex: heroin turns purple when added to the Marquis reagent, _____________________________

 Matter is anything that has ______ and takes up ________.  Elements are the building blocks of matter. They cannot be broken down into smaller pieces by chemical reactions.  Atoms are the smallest particle that can exist and keep the properties of the element.  Ex: a gold atom is still metallic and shiny

 Vertical columns – groups or families. All the elements have shared properties  Horizontal columns - series

 When two or more elements combine they form compounds  How many and what types of atoms are in each of the following compounds?  CO 2  CaCl 2  C 6 H 12 O 6

 Three physical states of matter:  SOLID, LIQUID and GAS  Solid – particles are held very closely together.  Shape and volume are _______  Liquid – particles can flow past each other  Volume is ________ but shape is ____________  Gas – particles are spread very far apart and are not attracted to each other  Shape and volume are _____________

 Matter can change from one state to another  Ex. Ice melts, from solid to liquid  This DOES NOT change the properties, only changes the way it looks  What are the following changes called?  Solid to liquid ______________  Liquid to solid ______________  Gas to liquid _______________  Liquid to gas _______________  Solid to gas ________________

 Phases occur when two substances are added to each other but will not mix  Ex. Oil and water  You can clearly see where one substance ends and the other begins

 Light is a wave  Light behaves as a continuous transverse wave  It has wavelength, and frequency  When white light passes through a prism it is dispersed into all the colors of visible light, which are ROYGBV  This occurs because light changes speed as it enters and leaves the prism. This is called refraction

The only difference between all of these types of waves is the frequency and wavelength of the wave.

 Lasers  Lasers produce coherent light, where the waves are all in unison with each other  This kind of light is very strong and intense

 Light is a Particle  Light behaves like a stream of energy particles called photons

 Some of the physical properties commonly used by forensic scientists to identify evidence:  Temperature  Weight and mass  Density  Refractive index

 Temperature measures the average kinetic energy of the molecules in a substance. The more heat they contain, the faster they move.  There are 3 difference temperature scales, Kelvin, Fahrenheit, and Celsius  We will primarily use Celsius

 Weight  How much gravity pulls down an object  Frequently measured in pounds  Depends on the gravity being exerted on the object  Ex: your weight is 1/6 of what it usually is when you’re on the moon  Mass  How much matter an object contains  Usually measured in grams or kilograms  Is the same no matter WHERE you are

 D = m / V  Density is an intensive property – it is the same for an object no matter what sample size is tested  The density of liquids and gases can change depending on what temperature they are at  Why? _________________________________  Density of a solid can be compared very easily with a gas or liquid. If it floats, it is less dense than the gas or liquid. If it sinks it is more dense.

 If a liquid has a volume of 620 mL and a mass of 480 g, what is its density?  The density of a piece of brass is 8.4 g/cm 3. If its mass is 510 g, find its volume.  What is the mass of water that occupies 150 mL? (Hint: Remember the density of water is 1 g/mL)  A brick has a density of 1.9 g/mL. Will it float in water? Why or why not?

 Refraction is when light bends as it changes from one substance to another. It does this because it travels at a different speed.  The refractive index of a substance tells us how much the speed changes and how much the light bends.

 Crystalline solids  Have a very orderly arrangement of atoms, forming a specific geometric pattern  All samples have the same arrangement  These refract a beam of light in two different rays. This is called double refraction  Birefringence – the difference in the two indexes of refraction for the two rays

 Amorphous solids  Have a random arrangement of atoms throughout  Might be a different arrangement for each sample  Glass is an amorphous solid  This is why different pieces of glass have different densities

 There are several steps to analyzing glass  Determine the composition of the glass  Compare glass fragments to each other and known sources of glass – see if broken edges match  Measure and compare the density of the glass  Determine and compare the refractive index of the glass  Classify the glass sample  Analyze glass fractures  Collect and preserve the glass evidence

 Glass is made by mixing sand with different metal oxides. There are many different types of class.  Float glass – molten glass is ‘floated’ on top molten tin. This is typically used for windows  Tempered glass – stronger than ordinary glass because it is rapidly heated and cooled while being made. It does not shatter into little pieces when broken  Laminated glass – a piece of plastic is layered in between two pieces of window glass

 Flotation method  A standard/reference piece of glass is places in a mixture of two liquids. The ratio of the mixture is adjusted until the glass is suspended in the middle. This means it has the same density as the liquid mixture.  Unknown glass chips of about the same size and shape as the reference are added to the liquid. If they are suspended with the reference sample then they have the same density. If they sink, they are more dense. If they float, they are less.

 Immersion method  Glass is sunk into a liquid.  The refractive index of the liquid is adjusted (usually by changing the temperature) until the glass and the liquid have the same refractive index.  You can tell because the glass pieces seem to disappear. Page 135 Figure 4-15

 When an objects hits a window, the glass bends. When it bends too far, the external side of the glass cracks first into radial fractures  Radial fractures are lines that ‘radiate’ from 1 spot  As the object keeps moving through the glass, the internal side of the glass breaks into concentric fractures  Concentric fractures circle a hole in the glass  See page139

 The hole created by an object moving at a high speed (bullet) is always wider on the exit side.  Stress markings also reveal which way an object went through the glass. (p 141 Figure 4-20)  3R rule. Radial cracks form a Right angle on the Reverse side of the force  Which hole happened first? Later radial fractures will end when they run into to previous radial fractures. p 141, Figure 4-21

 If the glass MIGHT be able to be pieced back together then ALL of it needs to be collected  Glass should be packaged in a solid container to keep it from breaking more  Clothes and/or shoes may be individually wrapped in paper and sent to the lab to look for glass fragments