Forensic Chemistry Basics

Forensic Chemistry

• First account of forensics: 1248, China, Song Ci
• Weapon used in first account: Sickle
• Song Ci's advances: Distinguished drowning from strangulation; identified murder, suicide, and accidents.

Chemical Analysis in Forensics

• Arsenic detection: Zinc and sulfuric acid are used.
• Poisoning analysis: Marsh test detects arsenic, antimony, and germanium.
• Arsenic detectability: 1700s

Chemistry Fundamentals

• Chemistry: Study of matter's composition, properties, and behavior.
• Matter: Anything with mass and volume. Defined by composition.
• Composition: Chemical makeup of something.
• Elements: All matter is made of elements.
• Elements on the periodic table: 118
• Forms of Matter:
  • Solid: Definite shape and volume.
  • Liquid: Indefinite shape, definite volume.
  • Gas: Indefinite shape and volume.
• Mixtures:
  • Heterogeneous: Components separable, identifiable.
  • Homogeneous: Uniformly distributed; components indistinguishable.
• Properties of Matter: Physical and chemical.
• Physical Properties: Observable without reaction.
  • Types: Intensive (independent of amount) and extensive (dependent on amount).
• Chemical Properties: Measurable only through a reaction.
• Hypothesis: Precise statement of a question and expected outcomes. Testable.
• Controls: Rules for experiment reproducibility.
• Types of Evidence: Physical and testimonial.
• Physical Evidence: Measurable or quantifiable data.
• Testimonial Evidence: Observations of a scientist or witness.
• Reconstructive Evidence: Notes taken at a crime scene after.
• Biological Evidence: Identification of human tissues.
• Trace Evidence: Microscopic physical evidence.
• Fingerprint Evidence: Latent (invisible) or patent (visible) prints.
• Impression Evidence: Impressions in softer materials.
• Firearm/Tool Mark Evidence: Marks left by tools impacting each other.
• Botanical Evidence: Fragments like wood, sawdust linking to a location or individuals.
• Document Evidence: Handwriting or typewriting for authentication.
• Qualitative Data: Observations.
• Quantitative Data: Raw numerical data.
• Derived Units: Based on base quantities via equations.

Units of Measurement

• Length: Meter (m)
• Mass: Kilogram (kg)
• Time: Second (s)
• Electrical Current: Ampere (A) - 1 coulomb per second.
• Temperature: Kelvin (K).
• Celsius to Kelvin Conversion: Add 273.15
• Amount of a Substance: Mole (mol) - 6.022 x 10²³
• Luminous Intensity: Candela (cd) - measure of light brightness

Mass and Weight

• Mass and Weight Interchangeability: Limited to Earth.
• Mass: Quantity of matter.
• Weight: Measure of gravitational pull.
• Units of Mass: Milligram (mg), Centigram (cg), Decigram (dg), Kilogram (kg).

Significant Figures

• Rules: Non-zero digits; zeros between non-zeros; trailing zeros after decimal points; leading zeros are non-significant.

Measurement Analysis

• Accuracy: 100 - ((|measured value - true value|)/(true value)) x 100%
• Standard Deviation: Quantifies data spread.
  • Small standard deviation: Values closely grouped, precise.
  • Large standard deviation: Values spread out, less precise.
  • Dimensional analysis: converting units.

Atomic Structure

• Democritus: Matter composed of tiny indestructible atoms.
• John Dalton's Postulates:
  • All matter is made of atoms.
  • Atoms of an element are identical.
  • Compounds are formed by combining atoms.
  • Chemical reactions rearrange atoms.
• Subatomic Particles:
  • Electrons: Negatively charged.
  • Protons: Positively charged, heavy.
  • Neutrons: No charge, heavy.
• Atomic Number: Number of protons.
• Isotopes: Atoms of the same element with different neutron counts.
• Protium, Deuterium, Tritium: Isotopes of hydrogen (varying neutron numbers).
• Atomic Mass: Sum of protons and neutrons.
• Finding Neutrons: Atomic mass - number of protons.
• Electron Location: Electron cloud around the nucleus
• Ion: Atom with unequal protons and electrons
  • Anion: More electrons than protons
  • Cation: More protons than electrons
• Neutral Atom: Equal numbers of protons and electrons.
• Shells: Regions where electrons are located in the electron cloud.

Chemical Bonding

• Chemical Bonds: Hold molecules together through electron sharing or charge differences.
  • Covalent: Shared electrons.
  • Ionic: Charge differences.

###Atomic Theory

• Monatomic Elements: Noble gases (elements that exist as individual atoms)
• Neils Bohr: Energy levels; Electrons are located around the nucleus.
  • Absorbance
  • Emittance
• Photon: Energy particle, carries light energy.

Light and Atoms

• Wavelength: Distance between wave crests.
• Frequency: Number of waves per unit time.
• Quanta and Quantum: Small bursts of emitted radiant energy; individual burst.
• Photoelectric Effect: Light on metal surfaces liberating electrons.
• Electron Liberation: Ultraviolet photons' energy releases electrons.
• Light Intensity Effect: High intensity means more released electrons, but not higher electron energy.

Explore the fundamentals of forensic chemistry, including historical cases and modern chemical analysis techniques. Understand how arsenic is detected and distinguish between different forms of matter. Dive into the role of chemistry in forensic investigations.