Download Chapter 1 The Nature of Chemistry Why Care about Chemistry

Why Care about Chemistry?
John W. Moore
Conrad L. Stanitski
Peter C. Jurs
Chemistry
The science of matter and the transformations it can
undergo.
http://academic.cengage.com/chemistry/moore
Chapter 1
The Nature of Chemistry
Stephen C. Foster • Mississippi State University
Why should you study it?
• It helps us understand our surroundings and the
way we function.
• It plays a central role in medicine, engineering and
many sciences.
Consider how chemistry impacts the availability of
clean drinking water.
Cleaning Drinking Water
Cleaning Drinking Water
In the 1960s UNICEF installed wells in Bangladesh:
This problem was recognized in the early 1980s:
• Surface water sources were often contaminated with raw
sewage.
• Dysentery and cholera were widespread.
Adding wells halved the mortality rate for children…
• Bacterial contamination was avoided.
…BUT replaced one problem with another
• Sediments just below the surface contain arsenic.
• Groundwater in the region is often contaminated with
arsenic.
Cleaning Drinking Water
In 2005 the U.S. National Academy of Engineering
announced a competition:
• Develop a method to reduce arsenic in drinking water to
safe levels.
• The prize: $1 million.
• 2007 winner: Chemist Dr. Abul Hussam (George Mason U.)
The winning SONO filter removes all common forms of
arsenic (As):
• H3AsO3
• H2AsO4• HAsO42-
• Symptoms of arsenic poisoning were noticed.
In the late 1990s:
• A major well-water testing program began.
• About 15% of tested wells were contaminated.
• In some places >80% of the wells were unsafe.
It’s a widespread problem in that part of the world:
• >100,000,000 people are exposed to arsenic-contaminated
drinking water.
Cleaning Drinking Water
A SONO filter
The red bucket contains three layers:
• 10 kg coarse river sand
• 5 - 10 kg CIM (composite iron matrix)
• 10 kg brick chips and coarse river sand.
The blue bucket contains:
•
•
•
•
10 kg coarse river sand
Charcoal (adsorbs organic material)
9 kg fine river sand
3.5 kg brick chips.
Clean drinking water emerges from the blue bucket.
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Cleaning Drinking Water
How Science is Done
In the red bucket:
• Atmospheric O2 converts H3AsO3 to H2AsO4- and
HAsO42• The CIM binds As to surface iron (=Fe):
=FeOH + H2AsO4- → =FeHAsO4- + H2O
=FeOH + HAsO42- → =FeAsO42- + H2O
• Observations are made.
The SONO filter:
• works well.
• does not further pollute the environment.
• costs very little.
• Experiments generate:
• A hypothesis is proposed.
• A tentative idea to explain the observations.
• Suggests further experiments to check if correct.
• A hypothesis: “arsenic can be removed by a filter”.
Qualitative data – no numerical information, or
Quantitative data - contains “numbers”
How Science is Done
How Science is Done
Qualitative or Quantitative?
A law summarizes a large number of experiments.
A SONO filter removes almost all arsenic from water.
Qualitative
A theory is a unifying principle to explain a body of facts
and the laws based on them.
Water processed by a SONO filter contains < 1 ppm
arsenic.
Quantitative
Identifying Matter: Physical Properties
Physical properties can be measured without
changing the composition of a substance.
A theory:
• is not contradicted by any known experiments.
• can predict unknown results.
• may be disproved in the future…
Physical Change
The same substance is present before and after a
physical change.
• physical state may change.
Examples
Temperature
Pressure
Mass
Volume
State (solid, liquid, or gas)
e.g. ice melts (solid water → liquid water).
Melting point
Boiling point
Density
Color
Shape of crystals
• gross shape may change.
e.g. a lump of lead is hammered into a sheet.
• size may change.
e.g. a piece of wood is cut in two.
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Melting and Boiling Point
Melting and Boiling Point
Temperature (T)
Measures relative energy (E) content of an object.
• E transfers from high-T to low-T objects.
U.S.:
Elsewhere:
often in degrees Fahrenheit (°F).
degrees Celsius (°C).
Water freezes
Water boils
Normal body T
T (°F)
32
212
98
T (°C)
0
100
37
water
boils
T (°C) = [T (°F) – 32] x 100
180
100°C
212°F
or
T (°C) = [T (°F) – 32] x 5
9
100
steps
180
steps
and
T (°F) = 9 [T (°C)] + 32
5
0°C
32°F
water
freezes
Density
Density
A physical property.
Density at 20°C
Substance
density =
mass
Volume
m
d=
V
d (g/mL)
ethanol
0.789
water
0.998
magnesium 1.74
aluminum
2.70
titanium
4.50
copper
8.93
lead
11.34
mercury
13.55
gold
19.32
A piece of metal (mass = 215.8 g) is placed into a
measuring cylinder where it displaces 19.1 mL of
water. Identify the metal.
Density at 20°C
Substance
Probably lead.
Water, copper and mercury
Dimensional Analysis
Example
Determine the mass of 3274 mL of mercury.
m = V x d = 3274 mL x 13.55 g = 4.436 x 104 g
1 mL
d (g/mL)
magnesium 1.74
aluminum
2.70
titanium
4.50
copper
8.93
lead
11.34
mercury
13.55
gold
19.32
d = m = 215.8 g = 11.3 g/mL
19.1 mL
V
Dimensional Analysis
Since 1 lb = 453.59 g we can write:
453.59 g = 1
1 lb
and
1 lb
=1
453.59 g
Example
What is the mass in grams of a 2000. lb car?
A proportionality (or conversion)
conversion factor was used..
2000. lb x 453.59 g = 9.072 x 105 g
1 lb
known units x desired units = desired units
known units
Multiplication by 1!
The quantity doesn’t change – just the units!
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Chemical Changes and Chemical Properties
Chemical Properties
Chemical property
A chemical reaction that a substance can undergo.
Describe these changes as a chemical or physical:
Chemical Reaction?
Reactants change into different substances.
(a) A cup of household bleach changes the color of
your favorite T-shirt from purple to pink.
Chemical change
(b) Fuels in the space shuttle (hydrogen and oxygen)
combine to give water and provide energy to lift
the shuttle into space.
Chemical change
Sucrose will caramelize, then form carbon on heating.
sucrose
reactant
heat
carbon + water
products
Classifying Matter: Substances & Mixtures
Mixtures are either:
• homogeneous
• two or more substances in the same phase.
• completely uniform.
(c) An ice cube in your glass of lemonade melts.
Physical change
Classifying Matter: Substances & Mixtures
Sample
heterogeneous
homogeneous
blood
air
apple
oil & vinegar dressing
• heterogeneous
• properties vary from point to point.
• may need a microscope to see variation.
milk
filtered ocean water
Blood appears homogeneous to the unaided eye, but not under a microscope.
“Homogenized” milk appears homogeneous, but not under a microscope.
Separation and Purification
Mixtures can be separated by physical methods.
e.g. magnetic separation of iron filings from sulfur
powder.
Classifying Matter: Elements & Compounds
Elements
Cannot be decomposed into new substances
Compounds
Can be decomposed
• Sucrose is composed of carbon, hydrogen and oxygen.
Have specific composition
• Sucrose is always 42.1% C, 6.5% H and 51.4% O by mass.
Have specific properties
• Water always melts at 0.0°C and boils at 100.0°C (1 atm.)
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Types of Matter
Nanoscale Theories and Models
Matter (may be solid, liquid, or
gas): anything that occupies
space and has mass
Heterogeneous matter:
nonuniform composition
Physically
separable into
macroscale objects are large enough to be seen,
measured and handled without any aids.
Homogeneous matter:
uniform composition throughout
Substances: fixed
composition; cannot
be further purified
Physically
separable into
Solutions: homogeneous
mixtures; uniform compositions
that may vary widely
microscale objects require a microscope to view
them.
nanoscale objects have dimensions ≈ an atom.
Chemically
separable into
Compounds: elements
united in fixed ratios
(nano: SI prefix for 10-9, so 1 nm = 1x10-9 m)
Elements: cannot be subdivided
by chemical or physical changes
Combine chemically
to form
Metric Units
States of Matter: Solids, Liquids & Gases
A decimal system.
Prefixes multiply or divide a unit by multiples of ten.
Prefix
kilo
deci
centi
milli
micro
nano
pico
Meaning
k
d
c
m
μ
n
p
103
10-1
10-2
10-3
10-6
10-9
10-12
Example
1 kilometer (km) = 1 x 103 meter (m)
1 decimeter (dm) = 1 x 10-1 m
1 centimeter (cm) = 1 x 10-2 m
1 millimeter (mm) = 1 x 10-3 m
1 micrometer (μm) = 1 x 10-6 m
1 nanometer (nm) = 1 x 10-9 m
1 picometer (pm) = 1 x 10-12 m
States of Matter: Solids, Liquids & Gases
KineticKinetic-Molecular Theory
“Matter consists of tiny particles in constant motion”.
Solid
• Closely-packed particles often in regular arrays.
• Fixed locations.
• Vibrate back & forth.
• Rigid materials.
• Small fixed volume.
• External shape often reflects inner structure.
The Atomic Theory
Liquid
• Particles are close, but farther apart than solids.
• Slightly larger, fixed volume than a solid.
• More randomly arranged than a solid.
• Constant collisions with neighbors.
• Less confined, can move past each other.
• All matter is made up of extremely small atoms.
atoms
Gas
• Continuous rapid motion.
• Particles are widely spaced.
• Travel large distances before colliding.
• No fixed volume or shape.
• Chemical reactions join, separate, or rearrange
• All atoms of a given element are chemically
identical.
• Compounds form when atoms of two or more
elements combine.
• usually combine in the ratio of small whole numbers.
atoms.
• Atoms are not created, destroyed or converted into
other kinds of atoms during a chemical reaction.
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The Chemical Elements
• Elements have unique names and symbols.
• From people, places, mythology…
The Chemical Elements
Element/symbol Discovery
Origin of Name
Carbon (C)
Ancient
L. carbo (charcoal)
Curium (Cm)
Seaborg et al.
1944
In honor of Marie and Pierre Curie
Nobel prize winners
Hydrogen (H)
Cavendish
1766
Gr. hydro (water) + genes (maker)
Mercury (Hg)
Ancient
Mythology: messenger of the gods
Gr. hydrargyrum (liquid
Titanium (Ti)
Gregor
L. Titans (1st sons of the earth)1791
Neon (Ne)
Ramsay & Travers Gr. neos (new)
1898
Polonium (Po)
M. & P. Curie
1898
• Symbols start with a capital letter.
• Extra letters are lower-case.
• Most symbols are obvious abbreviations
• Helium = He
Hydrogen = H
• Titanium = Ti
Zinc = Zn
• “Old”-element symbols come from ancient names.
• Gold = Au (aurum)
Tin = Sn (stannum)
• Silver = Ag (argentum)
Lead = Pb (plumbum)
Types of Elements
More than 110 elements are currently known
• 90 occur naturally on earth.
• the rest are man-made (synthetic).
• most are metals (only 24 are not).
Metals
• solids (except mercury – a liquid).
• conduct electricity.
• ductile (can be drawn into wires).
• malleable (can be rolled into sheets).
silver)
In honor of Poland
Types of Elements
Nonmetals
• Occur in all physical states.
• solids: sulfur, phosphorus, carbon.
• liquid: bromine
• gases: oxygen, helium, nitrogen.
Sulfur
• Do not conduct electricity.
• graphite (a form of carbon) is an exception.
Chlorine
Bromine & Iodine
Types of Elements
Six are metalloids:
metalloids
• boron
• silicon
• germanium
• arsenic
• antimony
• tellurium
They exhibit metallic and nonmetallic properties:
• Look like metals (shiny).
• Conduct electricity (not as well as metals).
• semiconductors.
Elements that Consist of Molecules
Most nonnon-metal elements form molecules.
molecules
A chemical formula shows the composition:
Diatomic examples:
H2
O2
N2
F2
Cl2
Br2
l2
Polyatomic examples:
O3
P4
S8
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Allotropes
Allotropes
Different forms of an element (same phase, same T, P)
Diamond
Graphite
Oxygen (gas):
• O2 (oxygen)
• O3 (ozone)
Carbon (solid):
• C (diamond)
• C (graphite)
• C60 (buckminsterfullerine) & other fullerines
• C (nanotubes)
Buckminsterfullerine
Communicating Chemistry: Symbolism
Chemical formulas show:
• Number and type of atoms in the molecule.
• Relative ratio of the atoms in a compound.
C12H22O11
sucrose
CH3OH
methanol
NaCl
table salt
Chemical equations show:
• How reactants convert into products.
C12H22O11
sucrose
heat
12 C
+ 11 H2O
carbon +
water
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