properties of matter. physical properties = a property that describes the behavior of a substance...

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

volumeLiquids• 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 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 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

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• 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 bendEX) 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.