Science question of the day…
 Why does cutting onions make you cry?
Answer!!!
 When you cut into an onion, a powerful acid sprays up
into the air. If your eyes are in the way of the spray
(which is likely if you are cutting onions), the acid,
while not damaging to your skin, will cause your eyes
to sting. Immediately, your lacrimal glands or tear
glands, go into overdrive. Your eyes start to tear, and
tears continue in excess until they’ve successfully
gotten rid of the irritation. Cool, huh?
Physical Properties of Matter
 Although everything is made of matter, they
all have different properties.
 Remember our metals vs. non-metals
experiment?
 Some properties we can test are physical
properties – properties that can be observed
or measured without changing the object, or
any of the materials it’s made of.
Physical Properties
 Some physical properties can change like mass and size
depending on how much of the object you have.
 Some physical properties never change like color, smell,
magnetism, and melting and boiling points.
 Take these items for example. What are the physical
properties you notice that are alike and different?
Physical Properties
 Texture is how the surface of the object feels.
 Malleability is the ability of a substance to be bent or
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hammered into sheets without breaking.
Ductility is the ability of the substance to be made into
thing threads without breaking.
Mass and Volume can be measured. We will learn how to
do this later. This is not necessarily the weight!
Density is the amount of mass that fits in a given volume.
Buoyancy is the ability to float in a liquid or rise in a gas.
Time for a little practice…
 Read “Physical Properties of Matter” and answer
questions 1-4 for homework. Number 5 is bonus. This
is due tomorrow!
Experiment: Volume, Mass, Density
 Click on the link entitled “Volume, Mass, and Density
Lab” located on my Science webpage.
 Use my login and password and follow the directions
to find the Density Lab Gizmo.
 Use the lab sheet and directions to find the volume,
mass, and density of the 12 items.
 Answer all questions and be ready to discuss your
results in class tomorrow!
Science question of the day…
 Contrary to popular adult belief, kids do not make your
hair turn gray, but what does?
Answer!!!
 It’s hard to imagine that those lovely locks of blond or
brunette hair on your head may someday change color so
dramatically. But your hair doesn’t turn white from a
lifetime of watching really scary horror movies. Instead, it’s
actually revealing its natural beauty. Hair loses much of its
color because it’s losing its melanin or carotene, which are
your body’s natural coloring substances (also known as
pigments). As you grow older, the pigment production in
hair follicles slows down and may eventually stop, cutting
off your hair’s supply of coloring and making it appear gray
or white. But your entire head of hair won’t turn gray
overnight; after all, this is a process that takes about 10-20
years.
Physical Changes
 Sometimes substances physical properties might change,
but this does not make it a different substance.
 Some physical changes are irreversible like cracking an egg
or breaking glass.
 Is this a physical change?
Physical Changes
 Inset Video Here
Time for a little practice…
 Read “Physical Changes of Matter” and answer
questions 1-4 for homework due tomorrow!
Science question of the day…
 Why is our galaxy called the “Milky Way?”
Answer!!!
 The Milky Way Galaxy is named for its milky
appearance. There’s a Greek poem that describes the
galaxy as “that shining wheel, men call it Milk.” To the
Greeks, the galaxy was called “Galaxias kuklos,” or
“Milky Band.” To the Romans, it was “Via Lactea,” or
“Road of Milk.” The Greek word for milk is “gala,” and
the word galaxy is derived from it. Human cultures
have different names for the Milky Way, like “Celestial
River” or “Celestial Road or Path.” It’s not really milk u
up there though. It is mostly noble gasses that have
accumulated together and reflect back light!
Physical Characteristics
 Last chapter we talked about physical characteristics
and using them to classify elements into their families.
 Much like physical characteristics, we can also classify
elements by their chemical characteristics.
 Which chemical characteristic did we test last week?
 I’ll give you a hint. It’s in your stomach, and it can also
be used to make lemonade. Gross…
Physical and Chemical
Characteristics and Changes
 These different characteristics tell us what kind of
reactions substances will have when energy is added or
taken away.
 Here is my example…
 We know that water will boil when we add the right
amount of heat. This is called the boiling point, and it
is a physical characteristic of water.
 This is a physical change in the substance.
Chemical Reactions and Changes
 There are several physical changes that substances can
go through. Let’s talk about this egg for example. What
kinds of changes could it go through?
 Which of these changes, if any, are irreversible?
 How else could we change this egg?
What do I need for a chemical
change to occur?
 Most chemical changes either require energy or release
energy.
 When the egg cooked, it required energy in order to
transform.
 When we burn a candle, it releases two kinds of
energy. What two kinds of energy are being released
from my candle?
Chemical Properties: Changes
 Just like physical changes, substances can undergo
chemical changes as well.
 You know you have a chemical change when new
substances are formed.
 This happens when the atoms are rearranged. The
same atoms are there, they are just put together
differently.
 Take the egg for example. When we cooked it, what
observations can you make about this cooked egg?
Chemical Reactions
 When we have a chemical change (like cooking the egg
to form a new substance) we create a chemical
reaction.
 The heat caused the chemicals in the egg to react and
become a solid.
 Does this type of reaction require energy or release
energy?
 It is called an endothermic reaction. It absorbs energy
from its surroundings.
Chemical Reactions
 We have another chemical reaction with my burning
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candle.
The wick lights and burns the wax, and part of the wax
becomes a gas.
Does this type of reaction require energy or release energy?
It is releasing energy! The wax requires energy to melt and
become a gas (physical change), but the wick is creating
energy to burn the wax
A reaction that creates energy is called exothermic.
Can you think of any other words that use the prefix ‘exo’?
How do I know it’s a chemical
change and not a physical change?
Physical
Chemical
 Observable and Measurable
 Buoyancy
-Mass
 Malleability -Volume
 Texture
-Density
 Shape
-Melting Point
 Ductility
-Boiling Point
 color
 New substance formed (not a
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change of state!)
Release or absorption of
energy
Color change
Light or heat given off
Bubbles
Physical vs. Chemical Changes
Next week…
 Next week you and a partner will determine what
physical and chemical changes can occur! You will be
given a bag of several items and you will experiment to
determine how you can change them.
 You will then create a Prezi to share with the class to
show your chemical and physical changes.
 Think about some ingredients and substances at home
this weekend that could be used to create physical and
chemical changes.
Time for a little practice…
 Read “Physical Changes vs. Chemical Changes” and
answer questions 1-4. Number 5 is bonus!
Science question of the day…
 Why is there no gravity in space?
Answer!!!
 Oh, but there is gravity in space! Astronauts only FEEL
like there is no gravity because they are continuously
falling as if there weren’t. You see, if there were no
gravity in space, the astronauts in their space ships
would fly off into space and not be able to come back!
 Imagine you have a piece of string with a ball on the
end. In this example, YOU are the EARTH, the
STRING is GRAVITY, and the BALL is a SPACE SHIP.
Now start swinging the ball around in a circle. You see
that the ball is pulling on you as you are pulling on the
ball. If you were to cut the string (that is, if there were
no gravity), then the ball would fly off into space.
 The difficult thing to realize is this: if you are
constantly pulling on the string — which you are as
you swing it around — why doesn’t the ball come to
you as it swings? It is because the ball is already in
motion around you. This is like the space ship; it is in
motion around the earth, and is continuously “falling”
towards the earth as the earth’s gravity pulls on it.
Characteristics of Chemical Change
 Whether or not a substance can go through a chemical
change is dependent on its chemical properties.
 The ability to burn is called combustibility.
 Wood, coal, candles, paper, etc. all have this chemical
property, and therefore can go through chemical
changes by being set on fire!
Characteristics of Chemical Change
 Another chemical property of elements is reactivity.
 Reactivity is how volatile an element is with other
elements.
 For example, the first column of the periodic table
contains highly reactive elements. They are looking to
pick fights with other elements and create explosions!
Characteristics of Chemical Change
 Another chemical property is stability.
 Stability is used to describe elements that do not react
easily with other substances.
 The noble gases in the far column of the periodic table
are examples of stable elements.
 Stable elements very rarely go through chemical
changes.
What are chemical reactions?
 There are four types of chemical reactions that occur
to create a chemical change: combustion,
decomposition, double replacement, and oxidation.
Chemical Reactions: Combustion
 A combustion reaction is an exothermic reaction in
which a substance combines with oxygen.
 It produces heat and light, like when a log is lit by a
match.
 The heat ignites the oxygen and other elements in the
wood which then burns and creates a new substance:
ashes.
Chemical Reaction: Decomposition
 A decomposition reaction is when a substance is
broken down into simpler substances.
 We see this when old trees rot in the woods. They
break down into the simpler elements they are made
of.
 Another example if when an electric current is passed
through water. The electricity (energy) breaks the
water down into hydrogen and oxygen.
 Don’t try that at home!
Chemical Reactions: Double
Replacement
 A double replacement reaction happens when ionic
compounds exchange ions with each other.
 This happens when two ionic compounds combine to
form one substance like sodium and hydrogen
chloride.
 They combine and form sodium chloride.
 Without this kind of reaction we wouldn’t have water!
Hydrogen and hydroxide ions combine to form
molecules in H2O!
Chemical Reactions: Oxidation
 An oxidation reaction occurs when a substance loses
electrons .
 This can happen in several ways, but we see this most
commonly when metals react with hydrogen and
oxygen in air and water.
 This is what produces rust on nails and the green
tarnish on copper.
Time for a little practice…
 Read “Chemical Changes and Chemical Properties”
and answer questions 1-4. Number 5 is not bonus
because we will be doing this in class.
Time for an Experiment…
 You will be analyzing substances to determine how
they can go through physical and/or chemical changes.
 Each group will be given a bag of items and
substances. Experiment with them and hypothesize
what will happen when they are combined or changed
by each other.
 You will use this week to experiment and then present
your information through a Prezi.
 Please see my website for more information!
Science question of the day
 How do glow sticks glow?
Answer!!!
Mixtures
 We have learned that pure substances are made of the
exact same element. No matter how you look at it, it
will always be the exact same makeup.
 But, in Chemistry, we can combine elements to make
compounds. They are no longer pure substances.
 Compounds are formed through chemical changes,
but even more common in nature are mixtures.
Mixtures
 Mixtures are combinations of two or more pure
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substances that are not chemically combined with one
another.
They do not have to be in the same proportions.
No matter how well they are blended together, their
molecules remain unchanged. They do not combine!
Some mixtures are easy to identify because you can see
their individual substances.
Think about the trail mix…
Solutions
 Solutions are a bit different from mixtures.
 In a mixture, the components can be added in
different sizes and proportions.
 In solutions, the components are mixed in equal
proportions.
 For example, if I took my trail mix and added the same
number and weight of raisins, nuts, and M&Ms it
would be a solution instead of a mixture.
Solutions
 Solutions can be made from solids, liquids, or gasses.
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However, the most common solutions are solids that
are dissolved in liquids.
Look at my Stevia. It is a solid.
Look at my water. It is a liquid.
The water is dissolving my sugar as I pour it in. This is
called my solvent. You “slove”nt for the solution!
The sugar that is dissolved is called my solute.
Mixtures and Solutions
Time for a little practice…
 Read “ Mixtures and Solutions” and answer questions
1-4. Number 5 is a bonus question.
Science question of the day…
 Why do fireflies light up?
Answer!!!
Separating Mixtures
 Since substances do not go through chemical changes,
they can be separated quite easily.
 They can be separated because of their physical
properties. To illustrate how mixtures can be separated
using physical properties we will do a little
experimentation!
Experiment
 Each table has some items they will use to separate a
mixture. Follow the directions on your bag and answer
the questions on your experiment sheet.
 You will present your findings on how you separated
your mixture in class tomorrow.
 Think about the physical characteristics at work in
your experiment!