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Science 8: Unit on Matter
Density – a comparison of mass (how much matter something has) and volume (how
much space something takes up)
-
how “compact” something is
the amount of matter for a certain volume of some substance
Density = Mass/Volume (mass ÷ volume)
Units are g/cm³ or g/mL
-
density is a constant property of matter
each pure substance has its own specific density, it doesn’t matter how much
of the substance you have
density of pure water is 1.0g/mL
an object sinks or floats in water depending on its density
Density > 1.0 Sink
Density < 1.0 Float
-
Density of liquids: liquids form layers depending on their densities
 The liquid with the lowest density will float on top
Matter – anything that has mass and takes up space
- made up of constantly moving particles with kinetic energy
- the speed of the particle movement changes with temperature
- as temperature↑ speed of the particles ↑ (adding heat energy)
Phases of matter
1. Solid – matter that has definite shape and definite volume
- examples:
2. Liquid – matter that has no definite shape, but has a definite volume
- examples:
3. Gas – matter that has no definite shape and no definite volume
- examples:
-
Particle Model of Matter – matter is made up of moving particles
Solid
- particles are
tightly packed
Liquid
- particles are
loosely packed
Gas
- particles are
very far apart
- low energy
- medium energy
- high energy
- strong bond
- bond stays connected
but stretches
- bond easily broken
Phase change:
adding heat energy will increase the motion of particles in a substance
(heating)
losing heat energy will decrease the motion of particles in a substance
(cooling)
every substance changes state at temperatures that are unique to that
substance
Melting – change of state from a solid to a liquid
Freezing – change of state from a liquid to a solid
Vaporization – change of state from a liquid to a gas
Boiling – vaporization throughout the liquid
Evaporation – vaporization from only the surface of a liquid
Condensation – change of state from a gas to a liquid on the surface of an
object (dew, clouds, steam, mist)
Sublimation – surface particles of a solid change directly to a gas (dry ice)
THE 'HEAT CURVE' FOR WATER
Properties of Matter
Physical – a property that can be observed without changing the substance into something
else
Examples: Phase of matter
Ability to dissolve
Color, odor, taste
Density
Hardness/texture
Flexibility
Conductivity
Chemical – a property that can only be observed by changing a pure substance into
something else
Examples: Flammability
Reactivity
Physical Change – when matter experiences a change in size, shape or phase
- changing the form or appearance of a substance but not the particles that
make up the substance
- examples:
Chemical Change – a change in matter that produces a new substance
- some evidence of chemical change is the production of heat or light, or the
appearance of gas bubbles
- examples:
Temperature: a measure of how fast the particles of matter are moving (kinetic energy)
Thermal Energy: the total energy of all the particles of matter
Heat: the energy that is transferred between objects because of a difference in
temperature
- High temperature → Low temperature
Thermal Expansion: as temperature increases the particles gain energy and move faster
and farther away from each other
-examples:
Energy and Chemical reactions:
 Exothermic – energy is released and temperature increases
o Heat given off
o Examples: burning

Endothermic – energy is absorbed and temperature decreases
o Examples: photosynthesis
Law of Conservation of Matter (Mass) and Energy: matter and energy cannot be created
or destroyed, they can only change form
Atomic Structure
Atomic Theory – all matter is made up of atoms
The atom is the smallest piece of matter that still has all the properties of
that substance
Particle
Charge
Location
Mass (AMU)
Electron
Proton
Neutron
Negative
Positive
No charge
Cloud
Nucleus
Nucleus
0
1
1_________
AMU = Atomic Mass Unit = 1.66 x 10 -24 grams
The atomic nucleus has a positive charge with tightly packed protons and
neutrons held together by a very strong bond
Element
Matter made of only one kind of atom
Cannot be broken down into any other substance by physical or chemical
means
Represented by a chemical symbol
o Gold – Au
o Oxygen – O
o Carbon – C
o Sodium – Na
Compound
A substance made up of two or more elements that are chemically
combined (bond) in a specific ratio
Represented by a chemical formula with subscripts
o Carbon Dioxide – CO2 1 carbon: 2 oxygen
o Carbon Monoxide – CO 1 carbon: 1 oxygen
Molecule
A particle of matter made up of two or more atoms held together by a
sharing of electrons
Mixture
Made up of two or more substances – elements, compounds, or both – that
are physically combined
Each substance keeps its characteristics
Each substance can be separated out by magnetism, filtering, vaporization
or distillation
Atomic Number
The number of protons in an atom of a certain element
The number of electrons in an atom of a certain element
# of protons = # of electrons
# of positive charges = # of negative charges
Atomic Mass
The total mass of the atom
The total number of protons plus neutrons in an atom of a certain element
Each proton and each neutron have a mass of 1 AMU
# of neutrons = atomic mass - atomic number
Periodic Table
Groups: vertical columns form families
o # 1-18
o Similar arrangement of electrons
Periods: horizontal rows
o # 1-7
Shell Diagram – see atom packet for diagram
Valence electrons
The electrons that are farthest away from the nucleus
They have the highest energy
Can be from 1 – 8 in number
The movement of valence electrons forms bonds between atoms by either
sharing the electrons or transferring them
Changing the number of neutrons and electrons
1. Cannot change the # of protons
Atomic # = # of protons
If you change the number of protons, you have a different atom
2. Adding or subtracting neutrons
Changes the total mass of the atom
Isotope – an atom of the same element with a different number of neutrons
3. Adding or subtracting electrons
Gives atoms a charge – positive or negative
Ion – a charged atom
o Positive ion – has lost one or more electrons
o Negative ion – has gained one or more electrons
Metals – have common physical properties
Hardness
Shininess/luster
Malleability – ability to be shaped
Ductile – can be pulled into wire
Conductivity – ability to transmit heat and electricity
Magnetism
…..and chemical properties
Reactivity – tendency to give up (lose) electrons and chemically combine with
other atoms
Non-metals – generally have physical properties opposite of metals
…….and chemical properties
Reactivity – tend to take up (gain) electrons or are non-reactive (Group #18)