Download ATOM (Ch 3)

ATOM (Ch 3)
• Smallest, most fundamental particle that
retains all physical and chemical
properties of an element.
• Atomic diameter = @1.0E-10 m
• Microscopic pictures show a range of
ways atoms arrange themselves: from
highly ordered crystals to disordered
amorphous solids.
MOLECULE (Ch 3)
• A molecule is a unit of matter that results
when 2 or more atoms are bonded
together.
• Can be separated into its constituent
atoms by chemical means, not physical
means.
• Has characteristic phys/chem properties.
• Most elements exist as single atoms, but
others exist as diatomic molecules (O2, H2)
CHEMICAL SYMBOLS
MOLECULAR FORMULAS
• The Periodic Table lists all known
elements in a shorthand notation called
chemical symbols (1- or 2- letter symbols).
• Compounds and molecules can also be
described in a shorthand notation called
molecular formulas. These include the
chemical symbols for the atoms and
numeric subscripts for the number of
atoms.
Examples of Chemical Formulas
• Atoms: H (hydrogen), He (helium), Ag (silver),
Hg (mercury), Cl (chlorine)
– All atoms are elements
• Molecules: H2 (hydrogen), Cl2 (chlorine), N2
(nitrogen)
– Some elements are molecules at room T, P
• Molecules: CH4 (methane), COCl2 (phosgene),
NaOCl (bleach), CH3CO2H (acetic acid), N2O
(laughing gas), NO2 (nitrogen dioxide), C9H8O4
(aspirin)
COLLOIDS
• Heterogeneous mixture in which particles
(size = 10-6 to 10-9 m) of one substance is
dispersed in another.
• The two substances in a colloid are not
soluble in each other and will separate
unless stabilized by emulsifiers.
• Table 1.2
STATES OF MATTER
• Solid: atoms are closely packed and are
relatively stationary; a solid maintains its own
shape and volume, and is incompressible.
• Gas: atoms are far apart and very mobile; a gas
takes the shape and volume of the container,
and is compressible.
• Liquid: has intermediate properties; a liquid
maintains its own volume but takes the shape of
the container, and is incompressible.
STATES OF MATTER AND
TEMPERATURE
The atoms of a solid at low temperature
remain fixed due to attractive forces. As
the temp. is raised, these attractive forces
are overcome by thermal motion and the
atoms move away from each other thereby
forming the liquid state. If the temp.
continues to increase, all attractive forces
are disrupted and a gas forms.
BEHAVIOR OF GASES
• Consider properties of gases: P, V, T
• How does V depend on T at constant P?
or V = f(T) stated mathematically.
As T  , then V ?
• V = f(P) at constant T? As P  , then V?
• Model of Ideal Gas: molecules (O2) are in
constant motion, collide elastically, move
faster as T  .
LIQUID CRYSTALS
• Liquid Crystals (0.05% of known cmps) have
properties intermediate between solids (highly
ordered) and liquids (flow slowly)
• Typical chemical structures are long organic
molecules that can line up in the presence of an
electric voltage or T change
• Typical applications are: LCD displays, dyes
(cholesterics), advanced materials (Kevlar,
Vectra), membranes, T measurement (by
changing colors), solvents for chemical analysis
METALS
• 75% of elements; all solid at room T and P
except mercury (liquid)
• Shiny, conductors of electricity and heat
(copper wire), malleable (gold leaf),
• Mercury: Hg, Z = 80, d = 13.6 g/mL,
deadly, UMD Chemistry eliminated nearly
all Hg from teaching program
• Hypoallergenic jewelry
METAL ALLOYS
• Alloy: mixture of metals to realize desired
properties: strength, hardness, resistance
to other cmps, malleability, weight
• Gold: Au, Z = 79, most malleable, very
soft, all refined gold = 60 cu ft volume
– Pure gold is 24 carat = 24K
• There are many alloys of gold with copper
(Cu), silver (Ag): 50% gold is 12K, 58% is
14K, 42% is 10K
METAL ALLOYS
• Stainless Steel: 74% Fe (iron), 18% Cr
(chromium) and 8% Ni (nickel)
• Steel: 99% Fe and 1% C (carbon)
• Aluminum cans: Al and Mn (manganese)
• Dental fillings: Hg and Ag amalgams