Intensive Chemistry
Day 2: Properties of Matter
Katy Johanesen
Ph.D. Candidate, USC Department of
Earth Sciences
This talk has two basic parts:
Properties of Matter
Physical Reactions
Properties of matter
• All matter has mass, volume, density, and
certain physical and chemical properties
• Dictated by the atomic or molecular structure
• Matter can be malleable, ductile, sectile,
magnetic, conduct heat or electricity, react
with water or oxygen…
• Color, phase at room temperature,
and hardness are also properties
Properties of compounds
• A compound does not have the same
properties as the elements that make it up.
• Table salt (NaCl) is edible and dissolves in water
• Sodium (Na) and Chlorine (Cl) are both poisonous
• Na metal reacts strongly with water
(our bodies are full of water)
• Cl2 was used as a poison gas in WWI
• http://www.youtube.com/watch?v=9bAhCHedVB4
Density
• Density = mass/volume
• Atomic mass of elements in the compound (mass)
• Phase/crystal structure of the compound (volume)
• CAUTION: weight ≠ mass!
• Weight is a force
• weight = mass times acceleration due to gravity
• Two minerals… use density and the periodic
table to determine which is which.
• Formulas: PbS and FeS2
Phases of matter
• Phase = a volume of space where all physical and
chemical properties are uniform
• Solid, liquid, gas, plasma
• Supercritical fluids and degenerate gases are other strange phases
of matter that do not naturally exist on Earth’s surface
• Form of matter depends on space between
molecules and energy of the system
• Energy = heat
Common phases of matter
• Solid = molecules are close together and ordered in a
crystal; energy of the system is the lowest
• Liquid = molecules are close together but are able to
move and switch places; energy in the system is
higher than in solid
• Gas = molecules are widely separated, move around
freely, move at high speeds; energy in the system is
the highest of all three
– Ideal gas law: PV=NkT
• http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=25
Definitions modified from http://www.enchantedlearning.com/physics/Phasesofmatter.shtml
Not so common phases of matter
• Plasma = gas composed of positively charged ions +
electrons; energy is so high matter becomes ionized;
makes up 99.9% mass of the solar system
• Ex: the sun, stars, fluorescent lamps, arc welding, lightning, plasma TV
• Supercritical fluid = when a liquid or a gas is
compressed and heated enough, their densities
become equal; no distinction between liquid and gas
beyond this pressure and temperature
• Found: deep within Earth, other planets
• Degenerate gas = gas compressed so hard that
atoms are touching; behaves like a solid
• Ex: white dwarf stars, neutron stars, metallic hydrogen (Jupiter, Saturn)
Definitions modified from http://www.enchantedlearning.com/physics/Phasesofmatter.shtml; background from dailymail.co.uk
Solids: crystal structure
• Atoms or molecules organize into regular,
repeating structures
• NaCl is ionically bonded
• CaCO3 contains ionic and covalent bonds
(CO32- is a covalently bonded ionic compound)
• Graphite and Diamond are both covalently bonded, but
have different properties due to the crystal structure
– Color
– Hardness
– Crystal shape
Solids: crystal structure
• Metals and Alloys: + ions bonded by
delocalized valence electrons
• Ductile: can be drawn into a wire (Cu, Au, Ag)
• Malleable: can be hammered into a sheet (Au, Pb, Al)
• Sectile: can be cut with a knife (Na, Au, Paper)
• Electric conductivity- electrons are free to move
through the material
Physical Reactions
•
•
•
•
Reversible
Change in state or phase
Change in shape or crystal structure
Mixture of two or more substances which can
be separated again
• What are some physical reactions you can
think of?
Phase transitions
• Matter can change
between phases with
enough change in energy
or pressure
• Each element (and
compound) can have a
different boiling point
(ptable.com)
Phase Diagram
Figures modified from Wikipedia
Ping-pong ball model of matter
• Balls represent atoms or molecules
• Shaking the container represents energy
(heat)
• What would happen if the same number of
molecules occupied a larger container?
Solutions
• Solutions are homogeneous mixtures
composed of one phase
• Solutes are dissolved in solvents
• Solutes and solvents can be any forms of
matter
–
–
–
–
–
–
–
Gas in gas (air, O2 in N2)
Liquid in liquid (vodka)
Solid in solid (steel)
Gas in liquid (soda)
Solid in liquid (salt water)
Liquid in gas (water vapor)
etc.
Source: http://commons.wikimedia.org/wiki/File:SaltInWaterSolutionLiquid.jpg
Solutions
• Solutions are physical, not chemical reactions;
can be separated to their constituent parts
– Can boil (or freeze!) seawater to remove water
from salt
– Can let soda go flat to remove carbon dioxide from
soda water
– Can boil amalgam to remove mercury from gold
(used in CA gold rush!)
Source: http://commons.wikimedia.org/wiki/File:SaltInWaterSolutionLiquid.jpg
Solutions: Acids and bases
• Acids and bases are ionic compounds that
dissolve and break apart in water to form
excess H+ or OH- ions
– The strength is based on the concentration of ions
• Acids are in lemons, vinegar, coffee, milk…
• Bases are in peppers, seawater, bleach, soap…
• Acids and bases can be solids, liquids, or gases
• most acids and bases we know are solutions in water
Brønsted-Lowry theory of
Acids and bases
• Acids are H+ donors; bases are H+ acceptors
– Recall that: H2O = H+ + OH– Another way of representing this is:
• H2O + H2O = H3O+ + OH-
• Example: Add HCl (gas, acid) to water:
– HCl + H2O = H3O+ + Cl-
• In this case, HCl is an acid because it donates the H+
to the water molecule, creating H3O+
Brønsted-Lowry theory of
Acids and bases
• Example: Add NH3 (gas, base) to water:
– NH3 + H2O = NH4+ + OH-
• In this case, NH3 is a base because it accepts
the H+ from the water (leaving extra OH- in
solution)
pH
• One way to quantify the
strength of acids and bases is
the pH scale
• pH = potential of Hydrogen
•
•
•
•
is a scale from 0-14
Pure water (neutral) is pH = 7
Acids are < 7
Bases are >7
pH indicators
• Indicators can tell us the pH of a
solution by changing colors when
added
• Litmus paper turns red in acid, blue
in base
• Phenolphthalein solution turns
purple when in a base, colorless in
an acid/neutral
• pH paper strips can accurately
measure pH from 0-14
pH
• Water breaks up to form a very
tiny percentage of H+ and OHions; most stay as bonded H2O
• H2O = [H+] + [OH-]
• Scale is a mathematical
representation of the
concentration of H+ ions
Introduction to Scientific Notation
• Scientific notation is used to represent very
large or very small numbers as exponents
• Often chemistry uses 10 as a base number
• 10,000,000 = 107 or
10×10×10×10×10×10×10
• 0.0000001 = 10-7 or 10/10/10/10/10/10/10
pH
• Normally when pure water
breaks into ions, it forms a ratio
of 10-7 H+ and 10-7 OH- ions for
every water molecule
– Based on the last slide, that
means for every ten million liters
of water, there is one gram of H+
(and OH-)
pH
• pH is a exponential scale based on
the strength of H+ ions
– pH 0 (acid) = [H+] = 100 or 1
• 1 gram of H+ per every 1 L of water
– pH 7 (neutral) = [H+] = 10-7
• 1 gram of H+ per every 10,000,000 L of
water
– pH 14 (base) = [H+] = 10-14
• 1 gram of H+ per every
100,000,000,000,000 L of water
• The higher the pH, the less H+ in
solution
Acids and Bases are useful
• Stomach acids break down our food
(digestion)
• Geologists use acids to digest rocks in the lab
• HF digests silica
• HCl digests iron
• Bases are great for cleaning (lye, bleach,
ammonia, soaps)