Properties of Matter

Physical 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.

We 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 System Scientists have used this system for over a century Created in 1791, it is based on units of 10

The English system is not based on any unit. It is based on things that change 1 foot changed depending on whose foot it was It is only used in the USA The metric system is used by every other country in the world In 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

Nature of Matter Matter = anything that has mass and takes up space. Matter is made of atoms Atoms are the simplest form of any element Elements are only made of one type of atom Everything that is matter is made of two or more of these elements http://www.ptable.com/ Periodic table = a chart of all of the known elements arranged in a systematic fashion

Vertical columns are called groups or families Things in the same column have similar properties Each element has a letter or letters as a symbol Many of the element’s symbols are in Latin EX) Gold = Au = Aurum (Latin for gold) When we combine elements, we get compounds Most everything on the planet is a compound or is made of compounds

Carbon dioxide is written as CO2, which means it has one atom of carbon and two atoms of oxygen. Carbon Dioxide is a new substance Carbon is a solid and Oxygen is a gas Carbon dioxide is a gas that does not act like either of these. -------------------------------------------------------------- States of Matter There are three states of physical matter – solid, liquid, gas

Solids The molecules in a solid are very tightly packed in a 3-D form The molecules are moving, but just barely by vibrating This gives solids a definite shape and a definite volume Liquids The molecules in a liquid move much faster than in a solid.

They move so fast that the 3-D form breaks down into chains of molecules They have no definite shape, but do have a definite volume Gases The molecules are now moving very quickly The liquid chains now are moving so fast that they break apart into individual molecules The have no definite shape and no definite volume.

Changing 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 H2O Sometimes a solid can turn directly into a gas. This is called sublimation

EX) 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 dangerous When there is a definite boundary between two substances it is called a phase - Ex) oil and water

This is one way forensic scientists can tell what a substance will be. --------------------------------------------------------------- Theory of light Knowing 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 particle Wave theory This says light travels in waves, like water

It 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 (.0000001) Frequency = how many times a wave passes a point in a given amount of time Its symbol is (f) f = c÷ʎ - OR: frequency = the speed of light divided by wavelength

Visible 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 dispersion The spectrum of visible light has 7 main colors: red, orange, yellow, green, blue, indigo and violet When light goes through something (glass, water, etc) is slows down.

Depending on what it is, it may slow down a little or a lot The is called Refraction When light bounces off something it is called Reflection Everything 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.

Light absorption is an important part of forensics. Certain chemicals will absorb and reflect certain colors. --------------------------------------------------------------- The electromagnetic spectrum This includes every wavelength that comes from the sun. Every wavelength from the sun travels at the speed of light (300 million meters/second)

This ranges from things that have a high frequency and short wavelength, to low frequency and long wavelength The highest frequencies belong to gamma rays These kill life because they have so much energy X-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

Ultraviolet 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 ----------------------------------------------------------------

Normally, 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 room We have found a way to make the rays stay in step with each other. This creates a light with only one wavelength This is a laser = light amplification by stimulated emissions of radiation. ----------------------------------------------------------------

Light as a particle In space, light acts like a wave. When it is absorbed by something, it acts like a particle Photon = energy particles of light Each photon has a specific amount of energy E = hf E is the energy of the photon h is Plank’s constant f is the frequency of the wave

In 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. ---------------------------------------------------------------

Refractive Index When light rays change speed, it will bend EX) quarter in a pool Light bounces off the quarter, through the water, and into the air When it hits the air, it speeds up a lot, and bends This 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.

The 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 589.3 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.

If 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.

Knowing if what you are looking at is a crystal or not will change how you figure out the refractive index. --------------------------------------------------------------- Forensic analysis of glass We 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.

Glass Composition Glass 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.

This 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”

These 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.