Chapter 3
Properties
and Changes of Matter
Review of 7th Grade
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An atom is a particle that cannot be
divided further without changing it’s properties
Elements
n
Elements are materials that cannot be
broken down into simpler materials without becoming a different kind of atom
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Simple definition – the different types of
atoms
Inside an Atom
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Nucleus – the center of an
atom
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Proton has a positive
charge and a mass of “1”
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Neutron has no charge and
a mass of “1”
n
Electrons have a negative
charge, orbit the nucleus, and have essentially no mass
Reading the Periodic Table
n
Atomic number tells the number of protons
and the number of electrons in a neutral atom of that element
n
Ex:
Atomic number for neon is 10, so it has 10 protons and 10 electrons
Reading the Periodic Table
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Atomic Mass: this is the total mass of the
atom and helps you figure out how many neutrons there are.
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Round the atomic mass (20 for neon)
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Subtract the atomic number (20-10 = 10) to
get the number of neutrons
Compounds
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A compound is a
substance whose smallest unit is made up of atoms of more than one element (can
be a molecule)
n
Written in formulas
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The subscript number tells
how many atoms of the preceding element are in the compound
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Ex: CO2
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No subscript is used when
only one atom of the element is present
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Ex: HCl
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A given compound is always
made of the same elements in the same proportion
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Ex: Water is always H2O, never HO2
or H3O
Physical Properties
n
A physical property is a
characteristic that can be observed without changing the composition of a
substance
n
5 general kinds
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Appearance
n
State of matter
n
Measurements
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Melting & Boiling Point
n
Magnetism
Appearance
n
Appearance
includes things that can be observed with the senses (touch, taste, smell,
sound, see)
n
Ex: The apple feels firm, tastes sweet, smells
like an apple, is very quiet, and looks red
States of Matter / Solubility
n
Solid
n
Liquid
n
Gas
Measurements
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Volume = amount of space
something occupies
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Mass = amount of matter in
an object
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Density = the amount of
mass in an object per unit volume
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D=M/V
n
It’s all about love
Melting & Boiling
n
Melting point – the temperature at which a solid changes to a liquid
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Boiling point – the temperature at which a liquid changes to a gas
Magnetism
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Describes how substances
can attract certain metals
Chemical Properties
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A chemical property is a
characteristic that cannot be observed without altering the substance
n
3 types
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Ability to burn
n
Tendency to rust
n
Reaction to other substances
Ability to Burn
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This depends on what the
material is made of and how unstable it is
n
You can’t tell until if it
is flammable for sure until you try – then the material is changed
Tendency to Rust
n
Iron is a major component
of steel
n
When iron is mixed with
oxygen (especially in the presence of water), it turns to iron oxide
n
But you can’t tell for
sure until you try
How it Reacts
n
Certain substances change when combined
n
Ex:
adding strong acids to bases causes a lot of heat to be released
Law of Conservation of Mass
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Matter – anything that takes up space
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Particles of matter are
not created or destroyed as the result of physical or chemical changes
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You cannot create matter
out of nothing or destroy matter
n
When you boil water, it
changes to steam, but the AMOUNT OF MATTER STAYS THE SAME
n
When you burn paper, you
produce ash, carbon dioxide, water vapor, smoke and you can see aflame, but the
AMOUT OF MATTER STAYS THE SAME
Physical Change
n
A physical change
occurs when the form or appearance of matter changes, but composition stays the
same
Physical Change
n Change the shape of a substance
Physical Change
n
Dissolving a solid into a liquid is a physical change
Physical Change
n
Changing states of matter
n
Solid à liquid
(melting)
n
Liquid à solid
(freezing)
n
Liquid à gas
(vaporization)
n
Gas à liquid
(condensation)
n
Solid à gas
(sublimation)
Chemical Change
n
Chemical change
results in a change in the substance’s composition
n
It becomes something new
n
Hard to reverse
Signs of a Chemical Change
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Changing the color
(not always)
Signs of a Chemical Change
n
Energy may be gained or released during a chemical change
Signs of a Chemical Change
n
Substances may change odor
as a result of a chemical change
Signs of a Chemical Change
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Formation of a gas or the
precipitation of a solid can indicate a chemical change
Chemical vs. Physical Change
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Chemical changes alter the composition
of a substance
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Part of substance or whole
substance becomes something new
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Ex: Burn a marshmallow
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Physical changes DO NOT alter the
composition of a substance
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All that happens is that
you change the appearance of the substance
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Ex: Squish a marshmallow
Word Equations (Chemical
Formulas)
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A word equation (also
known as a chemical formula) is a shorthand way of describing a chemical
reaction
n
They look like this:
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Listen + do assignments à pass
science
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6O2 + C6H12O6
ßà 6CO2
+ 6H20 + (energy)
Symbols Used
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There are some symbols you
need to understand to write chemical formulas
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“+” means that the two things listed
before this sign are combined with each other
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Ex: listen and do assignments
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“à” means “results in” or “produces.” In other words whatever the arrow points to
is what is produced in the chemical reaction
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Ex: results in passing the
class
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So how do you read:
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6O2 + C6H12O6
ßà 6CO2
+ 6H20 + (energy)
More Symbols
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( )
things in parenthesis are needed for the reaction to happen, but do not
actually take part in the reaction.
Generally this is going to be some form of energy.
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ßà A two-way arrow means that the reaction is
reversible
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6O2 + C6H12O6
ßà
6CO2 + 6H20 + (energy)
Products & Reactants
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Reactants are the substances that you start with in a chemical reaction
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Products are the new substances formed by the chemical reaction
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Example:
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Oxygen + food à carbon
dioxide + water + (energy)
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What are the products?
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What are the reactants?
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This is the chemical
reaction that describes how you digest your food and get energy from it
Examples
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If hydrogen peroxide is exposed to a
catalyst, it turns to oxygen and water
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What are the products?
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What are the reactants?
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How do you write the chemical formula?
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Hydrogen peroxide + (catalyst) à oxygen + water
Examples
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Magnesium dropped in hydrochloric acid
produces magnesium chloride and hydrogen gas
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What are the products?
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What are the reactants?
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What is the chemical formula?
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Magnesium + hydrochloric acid à magnesium chloride + hydrogen
Energy in Reactions
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Endothermic reaction – a chemical reaction
in which energy is absorbed as the reaction continues
n
Example:
Photosynthesis
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Carbon dioxide + water + (light energy) à sugar + oxygen
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Energy is needed for entire reaction
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What are the products?
n
What are the reactants?
Energy in Reactions
n
Exothermic Reactions – a chemical reaction
in which energy is released
n
Example:
burn fuel
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Oxygen + fuel à carbon dioxide + water + (energy)
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What are the products?
n
What are the reactants?
Examples
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Respiration
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Food + oxygen à water +
carbon dioxide + (energy)
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Burn magnesium
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Magnesium + oxygen à magnesium
oxide + (energy)
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Making aluminum requires
continually heating aluminum oxide
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Aluminum oxide + (energy) à aluminum +
oxygen