Chapter 3
Matter = stuff.
Matter is anything that has volume (takes up
space) and mass. All matter is made of atoms.
The atom is the smallest particle that retains
all physical and chemical characteristics
unique to the element.
Hydrogen
For example…
Every hydrogen atom is fundamentally
identical to every other hydrogen atom,
and fundamentally different from all
non-hydrogen atoms.
A hydrogen atom cannot be broken down
into smaller particles and still retain the
physical and chemical properties unique
to hydrogen..
Matter is described and categorized by its
properties or distinguishing characteristics.
Physical
properties can
be measured
without
changing the
composition of
the matter.
Chemical
properties
describe how
matter acts in
the presence of
other matter
Physical properties
density,
conductivity,
malleability,
hardness,
boiling point,
etc.
Why isn’t mass a
physical
property?
Chemical properties
Is it flammable?
Will it rust?
Does it tarnish?
Matter can divided into two main categories:
Pure substances and mixtures.
Pure Substances
Matter is a pure substance if the composition
does not change.
Common misconception: pure substances
are made of only one kind of atom.
Reality: Elements and compounds are both
pure substances.
Pure Substances
Element
•Made of one type
of atom.
•Cannot be
decomposed into a
simpler form and
still retain the
properties of the
matter.
Compound
Two or more
different elements
(different kinds of
atoms) chemically
bonded together to
form a new pure
substance.
Pure Substances - Compounds
In a compound, the component parts are
chemically bonded together; the atoms
cannot be separated by physical means
(evaporation, boiling, density, sorting, etc).
Na
Cl
Pure Substances - Compounds
A compound is represented by a chemical
formula that indicates exactly how many
atoms of each element form the compound;
it’s like a recipe that never changes.
What’s in your water?
Pure Substances - Compounds
Water is always H2O. Make one little change –
just add an oxygen – and it’s not water anymore.
H2O
H2O2
Pure Substances - Compounds
Composition can also be described as the
percent by mass:
Percent by mass = Mass of element x 100
Mass of compound
Pure Substances - Compounds
In 3.00 g of a compound containing only C and O,
there are 1.29 g of carbon. Determine the mass
percentages of the C and O.
In 5.00 g of a compound containing only C and O,
there are 1.36 g of carbon. Determine the mass
percentages of the C and O.
Are these the same compound?
Pure Substances - Compounds
Compound 1:
Compound 2:
42.9% C , 57.1 % O
27.3 % C , 72.7 % O
Different percent by mass = different composition
→ different compounds.
Pure Substances
Matter may undergo physical or chemical changes.
Physical
May change form,
appearance or state
of matter, but
composition is
unchanged.
Ice-water-steam
are all just H2O.
Chemical
In a chemical change
or chemical reaction,
new substances are
formed that have
different properties
from the original
substances.
Pure Substances – Chemical Changes
Sometimes the properties of the new compound
are VERY different from the properties of the
component elements.
Metal, explodes on
contact with water.
Table salt
2 Na(s) + Cl2(g) → 2 NaCl(s)
Poisonous yellow-green gas.
2 H2(g) + O2(g) → 2 H2O(l)
Pure Substances – Chemical Changes
Evidences that a chemical reaction has
happened are:
 Color change
 Gas release
Temperature change
Formation of a precipitate
Pure Substances – Chemical Changes
During a chemical reaction, matter can not
created or destroyed, although it may
change forms. This is the
Law of Conservation of Mass.
What goes in must also come out.
Pure Substances – Physical Changes
Physical
changes
affect matter
without
changing the
composition.
Pure Substances – Physical Changes
The fundamental difference between a solid,
liquid, and gas is the amount of kinetic energy
the atoms/molecules have.
Remember: Kinetic Energy is the energy of
motion.
Pure Substances – Physical Changes
The differences in KE causes variations in
atomic/molecular motion, packing,
compressibility, shape, and volume that are
characteristics of different states of
matter.
Pure Substances – Physical Changes
We discussed this in Physical Science; please
reacquaint yourself with the material. These will
help:
This website is linked from the class page.
http://www.chem.purdue.edu/gchelp/atoms/states.html
Read in Chapter 12 p. 402-403 “Kinetic
Molecular Theory” (up to “Explaining the
Behavior of Gases”), p. 415 “Liquids”, and p.
420 “Solids” and “Density of Solids” up to
“Crystalline Solids”.
Mixtures
The components are not chemically
bonded.
The composition varies.
The components retain their own unique
properties.
Can be separated using the physical
properties of the components.
Mixtures
In a
heterogeneous
mixture, the
different
components are
more easily
distinguished.
Mixtures
In a
homogeneous
mixture, the
substance
appears to be
uniform. The
component parts
are not easily
distinguished.
Mixtures
Homogeneous
mixtures are
also known as
solutions.