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Introduction to Chemistry

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Title: Introduction to Chemistry


1
Introduction to Chemistry
2
I. Chemistry is the study of all matter
3
Composition of Matter
Chemistry is lego-science. Millions of legos
form very complex structures, but the basic
building block is an individual lego.
So it also is with matter, all of the complex
structures that we see around us are composed of
basic building blocks. What are these called?
Matter and its Properties
Envision a huge box of legos, all the same color,
when we have the same type of atoms all grouped
together, what do we smart science types call
this?
Atoms The smallest unit of an element that
maintains the properties of that element.
Element A pure substance made of only one kind
of atom.
4
Elements
  • Gold
  • Silver
  • Hydrogen
  • Oxygen

5
Most substances on earth are not pure
  • Elements combine to form molecules
  • Salt (sodium chlorine)
  • Water (hydrogen oxygen)
  • Ozone (2 or 3 oxygen atoms together

6
  • ________________ - two or more atoms bonded
    together. Can have the same type of atoms or
    different types of atoms.

Molecules
7
Matter Mass, Weight and Volume
Matter is the basis of most of what we see, feel
and sense.
What matter ISNT
Matter is simply the amount of material (that is
atoms/molecules) that a substance is composed of.
Matter is not the space that an object takes up.
This is the volume of the object.
Matter and its Properties
While matter has volume, volume is NOT matter.
All matter takes up space (has volume) and has
mass.
8
Matter Mass, Weight, and Volume
So to determine the mass of a substance I simply
need to weigh it right?
No - Weight and mass are two different things.
Mass The measure of the amount of matter in a
substance.
Matter and its Properties
Mass is constant, it doesnt change depending on
your position.
Weight is a force, it depends on mass AND
gravitational pull or acceleration.
9
Your weight on other worlds
  • http//www.exploratorium.edu/ronh/weight/

10
What is mass?
  • Mass is the amount of matter in an object
  • Mass is constant

11
  • Weight The measure of the force of gravity on the
    mass of an object
  • Weight changes with gravity

12
Weight formula
  • 1 kg 2.2 pounds
  • Weight is mass times gravity
  • Gravity (g) 9.8 m/s2 - - round to 10
  • Weight Mass x Gravity
  • W m x g
  • Practice http//www.gcse.com/eb/gtest.htm

13
Question 1
  • The strength of gravity at the Earths surface is
    10 Newtons per kilogram. Calculate the weight of
    a car with a mass of 1500 kg.

W M X G
W 1500kg X 10 N/kg
W 15000 Newtons
14
Question 2
  • The strength of gravity on the moon is 1.6
    Newtons per kilogram. If an astronauts mass is
    80 kg on Earth, what would the mass be on the
    Moon?

80kg because the mass is constant. If the mass is
80 kg on Earth then it will be 80kg on the moon.
15
  • What is the difference between weight and mass?
  • Weight is the measure of gravity on an objects
    mass

16
COMPARE AND CONTRAST
  • MASS vs. WEIGHT
  • Amount
    Depends on gravity
  • Does not depend on gravity
    Weightmass x gravity
  • Constant
    Not constant



17
What about volume?
  • If two things weigh the same do they have the
    same volumes?
  • Can two things with the same mass have different
    volumes?

18
  • Volume the amount of space that matter in an
    object occupies

19
Measuring Volume
1. Graduated cylinders can be used to find the
volume of liquids and other objects.
Read the measurement based on the bottom of the
meniscus or curve. When using a real cylinder,
make sure you are eye-level with the level of the
water. What is the volume of water in the
cylinder? _____mL
43
the water molecule are attracted to the glass
molecules
Top Image http//www.tea.state.tx.us/student.asse
ssment/resources/online/2006/grade8/science/images
/20graphicaa.gifBottom Image http//morrisonlabs
.com/meniscus.htm
20
Measuring Liquid Volume
What is the volume of water in each cylinder?
37
52
Images created at http//www.standards.dfes.gov.uk
/primaryframework/downloads/SWF/measuring_cylinder
.swf
23
A
B
C
Pay attention to the scales for each cylinder.
21
Measuring Solid Volume
We can measure the volume of regular object using
the formula length x width x height.
_____ X _____ X _____ _____
Click here for an online activity about volume.
Choose Lessons ? Volume Displacement
22
Determine the volume of this cube.
5.7 cm
5.7 cm
5.7 cm
23
The answer is
Volume length x width x height l
5.7 cm w 5.7 cm h 5.7
cm V 5.7 cm x 5.7 cm x 5.7 cm
V 185.19 cm3
24
  • How do you find the volume of a solid using water
    displacement?
  • Place water in the graduated cylinder, drop in
    the solid object, measure the new water level,
    subtract

25
Lets look back at the questions
  • If two things weigh the same do they have the
    same volumes?

26
What about volume?
  • Can two things with the same mass have different
    volumes?

27
Newtons Laws of Motion
28
Background
  • Sir Isaac Newton (1643-1727) an English scientist
    and mathematician famous for his discovery of the
    law of gravity also discovered the three laws of
    motion. He published them in his book
    Philosophiae Naturalis Principia Mathematica
    (mathematic principles of natural philosophy) in
    1687. Today these laws are known as Newtons
    Laws of Motion and describe the motion of all
    objects on the scale we experience in our
    everyday lives.

29
  • If I have ever made any valuable discoveries, it
    has been owing more to patient attention, than to
    any other talent.
  • -Sir Isaac Newton

30
Newtons Laws of Motion
  • 1. An object in motion tends to stay in motion
    and an object at rest tends to stay at rest
    unless acted upon by an unbalanced force.
  • 2. Force equals mass times acceleration (F ma).
  • 3. For every action there is an equal and
    opposite reaction.

31
Newtons First Law
  • An object at rest tends to stay at rest and an
    object in motion tends to stay in motion unless
    acted upon by an unbalanced force.

32
Newtonss 1st Law and You
Dont let this be you. Wear seat belts. Because
of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 m/hour.
33
What does this mean?
  • Basically, an object will keep doing what it was
    doing unless acted on by an unbalanced force.
  • If the object was sitting still, it will remain
    stationary. If it was moving at a constant
    velocity, it will keep moving.
  • It takes force to change the motion of an object.

34
What is meant by unbalanced force?
If the forces on an object are equal and
opposite, they are said to be balanced, and the
object experiences no change in motion. If they
are not equal and opposite, then the forces are
unbalanced and the motion of the object changes.
35
Some Examples from Real Life
A soccer ball is sitting at rest. It takes an
unbalanced force of a kick to change its motion.
  • Two teams are playing tug of war. They are
    both exerting equal force on the rope in opposite
    directions. This balanced force results in no
    change of motion.

36
1st Law
  • Once airborne, unless acted on by an unbalanced
    force (gravity and air fluid friction), it
    would never stop!

37
1st Law
  • Unless acted upon by an unbalanced force, this
    golf ball would sit on the tee forever.

38
Newtons First Law is also called the Law of
Inertia
  • Inertia the tendency of an object to resist
    changes in its state of motion
  • The First Law states that all objects have
    inertia. The more mass an object has, the more
    inertia it has (and the harder it is to change
    its motion).

39
More Examples from Real Life
A powerful locomotive begins to pull a long line
of boxcars that were sitting at rest. Since the
boxcars are so massive, they have a great deal of
inertia and it takes a large force to change
their motion. Once they are moving, it takes a
large force to stop them.
On your way to school, a bug flies into your
windshield. Since the bug is so small, it has
very little inertia and exerts a very small force
on your car (so small that you dont even feel
it).
40
If objects in motion tend to stay in motion, why
dont moving objects keep moving forever?
Things dont keep moving forever because theres
almost always an unbalanced force acting upon it.
A book sliding across a table slows down and
stops because of the force of friction.
If you throw a ball upwards it will eventually
slow down and fall because of the force of
gravity.
41
In outer space, away from gravity and any sources
of friction, a rocket ship launched with a
certain speed and direction would keep going in
that same direction and at that same speed
forever.
42
Newtons Second Law
  • The net force of an object is equal to the
    product of its mass and acceleration, or Fma.

Acceleration a measurement of how quickly an
object is changing speed.
43
What does F ma mean?
  • Force is directly proportional to mass and
    acceleration. Imagine a ball of a certain mass
    moving at a certain acceleration. This ball has
    a certain force.

Now imagine we make the ball twice as big (double
the mass) but keep the acceleration constant. F
ma says that this new ball has twice the force
of the old ball.
Now imagine the original ball moving at twice the
original acceleration. F ma says that the ball
will again have twice the force of the ball at
the original acceleration.
44
More about F ma
  • If you double the mass, you double the force. If
    you double the acceleration, you double the
    force.
  • What if you double the mass and the acceleration?
  • (2m)(2a) 4F
  • Doubling the mass and the acceleration quadruples
    the force.
  • So . . . what if you decrease the mass by half?
    How much force would the object have now?

45
What does F ma say?
F ma basically means that the force of an
object comes from its mass and its acceleration.
Something very massive (high mass) thats
changing speed very slowly (low acceleration),
like a glacier, can still have great force.
Something very small (low mass) thats changing
speed very quickly (high acceleration), like a
bullet, can still have a great force. Something
very small changing speed very slowly will have a
very weak force.
46
2nd Law
F m x a
47
2nd Law
  • The net force of an object is equal to the
    product of its mass and acceleration, or Fma.

48
2nd Law
  • When mass is in kilograms and acceleration is in
    m/s/s, the unit of force is in newtons (N).
  • One newton is equal to the force required to
    accelerate one kilogram of mass at one
    meter/second/second.

49
2nd Law (F m x a)
  • How much force is needed to accelerate a 1400
    kilogram car 2 meters per
  • Write the formula
  • F m x a
  • Fill in given numbers and units
  • F 1400 kg x 2 meters per second
  • Solve for the unknown
  • 2800 kg-meters/second or 2800 N

50
2nd Law (F m x a)
  • What acceleration will result when a 12 N net
    force applied to a 3 kg object?
  • Write the formula
  • F m x a
  • Fill in given numbers and units
  • 12N 3 kg x a meters per second
  • Solve for the unknown
  • 12N 3 kg x 4 meters per second

51
Check Your Understanding
  • 1. What acceleration will result when a 12 N net
    force applied to a 3 kg object?
  • 12 N 3 kg x 4 m/s
  •  
  • 2. What acceleration will result when a 12N net
    force applied to a 6 kg object?
  • 12 N 6 kg x 2 m/s
  • 3. A net force of 16 N causes a mass to
    accelerate at a rate of 5 m/s2. Determine the
    mass.

  • 16 N 3.2 kg x 5 m/s
  •  

52
If mass remains constant, doubling the
acceleration, doubles the force. If force remains
constant, doubling the mass, halves the
acceleration.
53
If mass remains constant, doubling the
acceleration, doubles the force. If force remains
constant, doubling the mass, halves the
acceleration.
54
Newtons 2nd Law proves that different masses
accelerate to the earth at the same rate, but
with different forces.
  • We know that objects with different masses
    accelerate to the ground at the same rate.
  • However, because of the 2nd Law we know that they
    dont hit the ground with the same force.

F ma 98 N 10 kg x 9.8 m/s/s
F ma 9.8 N 1 kg x 9.8 m/s/s
55
Newtons Third Law
  • For every action there is an equal and opposite
    reaction.

56
What does this mean?
For every force acting on an object, there is an
equal force acting in the opposite direction.
Right now, gravity is pulling you down in your
seat, but Newtons Third Law says your seat is
pushing up against you with equal force. This is
why you are not moving. There is a balanced
force acting on you gravity pulling down, your
seat pushing up.
57
Think about it . . .
What happens if you are standing on a skateboard
or a slippery floor and push against a wall? You
slide in the opposite direction (away from the
wall), because you pushed on the wall but the
wall pushed back on you with equal and opposite
force.
Why does it hurt so much when you stub your toe?
When your toe exerts a force on a rock, the rock
exerts an equal force back on your toe. The
harder you hit your toe against it, the more
force the rock exerts back on your toe (and the
more your toe hurts).
58
Other examples of Newtons Third Law
  • The baseball forces the bat to the left (an
    action) the bat forces the ball to the right
    (the reaction).

59
3rd Law
  • Consider the motion of a car on the way to
    school. A car is equipped with wheels which spin
    backwards. As the wheels spin backwards, they
    grip the road and push the road backwards.

60
3rd Law
The reaction of a rocket is an application of the
third law of motion. Various fuels are burned in
the engine, producing hot gases. The hot gases
push against the inside tube of the rocket and
escape out the bottom of the tube. As the gases
move downward, the rocket moves in the opposite
direction.
61
Review
Newtons First Law
Objects in motion tend to stay in motion and
objects at rest tend to stay at rest unless acted
upon by an unbalanced force.
Newtons Second Law
Force equals mass times acceleration (F ma).
Newtons Third Law
For every action there is an equal and opposite
reaction.
62
Vocabulary
Inertia the tendency of an object to resist
changes in its state of motion
Acceleration a change in velocity a
measurement of how quickly an object is changing
speed, direction or both
Velocity The rate of change of a position along
a straight line with respect to time
Force strength or energy
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