INTRODUCTION TO FORENSIC CHEMISTRY

• 1.1 Welcome• 1.2 Chemistry, Crime, & the Global Society• 1.3 Physical Evidence: Matter & Its Forms• 1.4 The Periodic Table• 1.5 Learning the Language of Chemistry• 1.6 The Most Important Skill of a Forensic

Scientist: Observation• 1.7 Scientific Method• 1.8 Case Study Finale: Whose Side Are

They On?

INTRODUCTION TO FORENSIC CHEMISTRY• Forensics means “of the forum” – for public debates and

trials – can be introduced into legal procedings

– Forensic Science requires knowledge of biology, physics, geology, psychology, and chemistry, in particular, and more.

• Physical Evidence: Matter & Its Forms– Matter exists as solids, liquids, or gases

• Liquids resist being compressed

• Gases are compressible

The universe is composed of matter and energy.

Matter is composed of mixtures and pure substances.

In matter: There are two kinds of pure substances and two kinds of mixtures.

Matter is composed of mixtures and pure substances.• Mixtures involve a physical blending of two or more

“pure substances.”– mixtures can be separated into their components by physical

means such as evaporation or filtering – Homogeneous mixtures have uniform properties and

composition, for example, solutions (KoolAid).– Heterogeneous - variable composition, and often show

visible differences (Chocolate chip cookies).

1.3 PHYSICAL EVIDENCE: MATTER AND ITS FORMS

• Pure substances have uniform composition (elements and compounds)

– their components can’t be separated by physical means such as distillation.

• Pure substances are composed of:– Elements. These contain only one type of atom. Fe, Na, As, etc.– Compounds. These contain two or more types of atoms. H2O,

NaCl, KNO3, etc.• Compounds are of two types:

– Molecular (covalent bonding), such as water, alcohol, sugar, or CO2.

– Ionic, such as salt, NaCl, or baking soda, NaHCO3.

1.3 PHYSICAL EVIDENCE: MATTER AND ITS FORMS

A lead (Pb) bullet, a homogeneous

mixture, contains traces of impurities

such as bismuth, Bi, and antimony, Sb.

Add in the dirt here, and the whole

sample becomes a heterogeneous

mixture.

Differences are usually visible.

Figure 1.2 (c), pg. 7

Investigating Chemistry, 2nd Edition

© 2009 W.H. Freeman & Company

Can you sort the elements, compounds and mixtures?

Pure: a, b, d Element: b Compound a, dMixture: c, e Heterogeneous: c Homogeneous: eSolutions are homogeneous.H2, Fe, salt water, wet sand (SiO2), pure baking soda (NaHCO3), gasohol, ice-water (s + l).

Identify each of these as a pure substance or a mixture • then as either an element or a compound or as a homogeneous or heterogeneous mixture.

Introduction to the Periodic Table

• Symbols for the chemical elements are usually the first letter or the first and second or first and third letters.

• Examples include H for hydrogen, C for carbon, Ca for calcium, Zn for zinc, He for helium, and Mg for magnesium.

• Some elements were named by alchemists using Latin:

(These elements were known from antiquity.)

– Na for sodium, K for potassium, Au for gold, and Ag for silver, Sb for antimony.

– Hg for mercury, Fe for iron, Pb for lead, Cu for copper, Sn for tin, etc.

• Copper, silver, and gold still occur free in nature.

• You are responsible for knowing the symbol and name for elements 1-95.

• The table can be divided into metals, nonmetals, and metalloids.– The metals predominate. They conduct heat and

electricity well. Mercury is the only liquid at room temperature.

– The nonmetals are poor conductors, except for graphite, C.

– Metalloids include: boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine. They conduct electricity at high temperatures.

Introduction to the Periodic Table

THE MOST IMPORTANT SKILL OF A FORENSIC SCIENTIST: Observation and the Scientific Method• Observation is the most

important skill:– It is the first step in the

scientific method.

• It requires good judgment and experience to select the key evidence at a crime scene. Critical thinking is essential.

• It means being logical, rational, impartial, and analytical.

2. How are gases characterized?

A) By small distances between particles that are moving at low speeds

B) By small distances between particles that are moving at high speeds

C) By large distances between particles that are moving at low speeds

D) By large distances between particles that are moving at high speeds

4. A molecule is defined as an atom.

 A)True

 B) False

6. Sugar in tea is an example of what?

 A) A complete mixture

 B) An incomplete mixture

 C) A heterogeneous mixture

 D) A homogeneous mixture