Measuring Matter
Chapter 1
Sections 2 and 3
Mass/Weight
• Your weight is a measure of the force of
gravity on you.
• The mass of an object is the measurement of
how much matter an object has.
• The mass of an object is the measurement of
how much matter it contains.
• Unlike its weight, an object’s mass will not
change if the force of gravity on it changes.
Units of Mass
• To measure the properties of matter,
scientists use a system of units called
the International System of Units (SI)
• For mass the SI unit is kilogram.
• If you weigh 90 pounds on Earth, then
your mass is approximately 40
kilograms.
Volume
• The amount of space that matter occupies is
called its volume.
• It’s easy to see the volume of a liquid but
gases have volume, too.
• Think about a balloon as you blow it up.
• For rectangular objects such as a block of
wood, the volume is found by multiplying
length x width x height.
• Volume is measured in cubic centimeters,
meters, millimeters, etc.
Density
• Density relates the mass and volume of
an object or material.
• To calculate the density of a sample,
divide its mass by its volume.
• Density = mass
volume
Particles of Matter
Chapter 1
Section 3
Atoms
• An atom is the smallest particle of an
element.
• A molecule is a group of atoms that are
joined together and act as a single unit.
• The force that holds two atoms together
is called a chemical bond.
Democritus
• One of the first people known to have thought
that matter is formed of small pieces was
Democritus a Greek philosopher who lived
about 440 B.C.
• He thought that there were smallest possible
“pieces” of everything, and that you could
chop matter into ever smaller pieces until you
got to its smallest piece.
• Democritus called this smallest piece atomos,
which is Greek for “uncuttable”
Dalton’s Ideas
• In 1802, an atomic theory - a theory about atoms was proposed by a British schoolteacher named
John Dalton.
• His main conclusions were that atoms can’t be
broken into smaller pieces.
• Dalton thought atoms were like tiny marbles, or
rigid spheres that are impossible to break.
• In any element all the atoms are exactly alike.
• Atoms of different elements are different.
• Atoms of each element have a unique mass.
• The masses of the elements in a compound are
always in a constant ratio.
Dalton’s Ideas cont.
• Today, scientists have identified some
important exceptions to Dalton’s
statements.
• However, Dalton’s ideas form the basis
of understanding atoms.
Atoms and Molecules
• A molecule is group of atoms that are joined
together and act a single unit.
• The force that holds two atoms together is
called a chemical bond.
• Molecules can contain as many as a billion
atoms or as few as two atoms.
• How small are atoms?
• There are about 2,000 billion billion atoms of
oxygen in one drop of water.
How we can see atoms
• The machine used to magnify things so
that we can capture images of atoms is
called a scanning tunneling microscope.
• Look on page 33, Figure 15, to see the
picture of a model of an atom.