2. protons (nucleus) – positively charged particles
neutrons (nucleus) – particles with no charge
electrons ( in orbit) – negatively charged particles
All matter is composed of atoms
The Atom
3. The Periodic Table
element – a substance that cannot be chemically broken down
atomic number – number of protons and electrons an element possesses
mass number – sum of protons and neutrons in a particular element
4. Compounds
- a substance made up of two or more elements
H2O
CO2
O2
NH3
O
O O
O O
C
N
O
O O
CO O
N
N
18
44
32
17
5. Compounds
O O
N
Two types:
Organic Compounds – chemical compounds composed mostly of carbon and
hydrogen (may contain N, O, S, P and other atoms as
well)
All of the chemical compounds we will talk about in
forensics this term will be organic compounds.
Inorganic Compounds – chemical compounds resulting from reactions of any
and all the other elements on the periodic table
Of the 22 million compounds known to man, 20 million of them are organic.
6. Chemical Bonding
Two types:
Ionic Bonding – attraction between a positive atom (ion) and a negative atom
(ion); many inorganic substances interact via ionic bonds
Covalent Bonding – where two atoms share electrons; organic compounds
always share electrons to make bonds
Most of the chemicals we will talk about in forensics will involve covalent
bonds!
Na + Cl
_
O
7. Important Chemical Properties
Electronegativity – the degree to which atoms attract electrons (increases
up and to the right on the periodic table)
fluorine, oxygen, nitrogen, chlorine, bromine - some of the most electronegative
8. Important Chemical Properties
Electronegativity within compounds leads to a concept called polarity.
Polarity is an imbalance in the position of electrons in a compound due
to differing electronegativities of the individual atoms; the electrons
are attracted to one side (top vs bottom, left vs right) of a compound
more than the other.
The way they are drawn, which of the following compounds are polar?
O
CO O
N
Cwater
carbon dioxide
methane
ammonia
9. Important Chemical Properties
Polarity leads to a phenomenon known as intermolecular forces.
Intermolecular (IM) forces are the forces that attract one molecule to
another – an attraction between molecules.
There are three types of IM forces that we will consider in forensics:
a. Dipole-dipole
b. Hydrogen bond ( a type of dipole-dipole)
c. London forces
Polarity influences the way chemicals interact (their behavior) through
IM forces.
10. Chemical Reactivity
There are two factors that affect the reactivity of a chemical compound
(two, at least, that we will consider in this class):
a.shape of the molecule
b. the energy of the reactants vs the energy of the products in
a reaction
Reactants Products
Oklahoma City 1995
