Criminalistics: Chapter 10 - Matter, Light, and Glass Examination

Forensic Scientist's Role: Must determine properties that give matter distinguishing characteristics and unique identity.
Physical Properties: Describe a substance without reference to any other substance.
- Examples include weight, volume, color, boiling point, and melting point.
Chemical Property: Describes the behavior of a substance when it reacts or combines with another substance.

Matter: Anything that has a mass and occupies space.
Element: The simplest known substance and the fundamental building block of all matter.
- All elements are listed by name and symbol in the periodic table (Refer to Figure 10–1).
Compound: Formed when two or more elements combine.
- It is a pure substance composed of one or more elements.
- Atom: The basic particle of an element.
- Molecule: The smallest unit of a compound.

Matter can be classified by its physical form:
- Solid: Possesses a definite shape and volume.
- Liquid: Has a specific volume, but takes the shape of its container.
- Gas/Vapor: Has neither a definite shape nor a definite volume.
Phase Changes: Substances can transition from one phase to another without forming a new chemical species; it's a change in physical state.
Visible Boundary: Different phases exist wherever a substance can be distinguished by a visible boundary.

Metric System: The universal system of measurement used by scientists.
- Basic units of measurement:
  - Length: Meter ( ext{m} )
  - Mass: Gram ( ext{g} )
  - Volume: Liter ( ext{L} )
- Common Prefixes:
  - deci ( 10^{-1} )
  - centi ( 10^{-2} )
  - milli ( 10^{-3} )
  - micro ( 10^{-6} )
  - nano ( 10^{-9} )
  - kilo ( 10^{3} )
  - mega ( 10^{6} )
- Equivalencies: For length, 2.54 centimeters ( ext{cm} ) = 1 inch ( ext{in} ).

Definition: A measure of heat intensity, indicating the hotness or coldness of a substance.
Celsius Scale: The most commonly used temperature scale in science.
- Freezing point of water is assigned 0^ ext{o} ext{Celsius} .
- Boiling point of water is assigned 100^ ext{o} ext{Celsius} .

Weight: The force with which gravity attracts a body.
Mass: Refers to the amount of matter an object contains, independent of gravity.
- Determined by comparison to the known mass of standard objects.

Definition: Mass per unit volume.
- Expressed by the formula: ext{Density} = rac{ ext{Mass}}{ ext{Volume}}
Intensive Property: Density remains the same regardless of sample size.
Characteristic Property: It is a distinct property that aids in the identification of a substance.
- A simple procedure to determine density involves measuring mass on a scale and volume by water displacement (Refer to Figure 10–2).

Light Behavior: Light waves travel at a constant velocity in air but slow down and bend when penetrating another medium (e.g., glass, water).
Refraction: The bending of light waves due to a change in their velocity.
Refractive Index (RI): The ratio of the velocity of light in a vacuum to its velocity in the medium under examination.
- Expressed by the formula: ext{Refractive Index} = rac{ ext{Velocity of light in vacuum}}{ ext{Velocity of light in medium}} (Refer to Figure 10–3).
- Example: At 25^ ext{o} ext{Celsius} , the refractive index of water is 1.333 , meaning light travels 1.333 times faster in a vacuum than in water.
Intensive Property: Like density, refractive index is an intensive property and is characteristic for a substance.
Crystalline Solids: Have definite geometric forms due to ordered atomic arrangement.
- Refract a beam of light into two different light-ray components, leading to double refraction.
- Birefringence: The numerical difference between these two refractive indices.
Amorphous Solids: Do not have a crystalline structure (e.g., glass, which has a random atomic arrangement).

Models of Light: Two main models describe light's behavior:
- Continuous Wave Model: Describes light as a continuous wave.
- Discrete Energy Particle Model: Depicts light as a stream of discrete energy particles.
Dispersion of White Light: When white light passes through a prism, it is dispersed into a continuous spectrum of colors (Refer to Figure 10–5).
Electromagnetic Spectrum: The entire range of radiation energy, from highly energetic cosmic rays to less energetic radio waves.
- Visible light is only a small portion of this spectrum.
- Visible light ranges in color from red to violet.
Wave Description: Waves are characterized by:
- Wavelength: The distance between two successive crests (or troughs).
- Frequency: The number of crests ( or troughs) passing a given point per unit of time (Refer to Figure 10–6).
- Relationship: Frequency and wavelength are inversely proportional to one another.
Particle Description: Once electromagnetic radiation is absorbed by a substance, it is best described as discrete particles of light known as photons.

Definition: A hard, brittle, amorphous substance composed primarily of silicon oxides (sand) mixed with various metal oxides.
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