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Eighth Grade Review
Matter is anything that has mass and
occupies space. All matter is made up of
small particles called atoms.
Matter can exist as a solid,
liquid, gas or plasma
Matter can be classified as elements,
compounds, and mixtures
The
atoms of
any
element
are alike
but are
different
from
atoms of
other
elements
Mixtures also consist of two or
more substances, but the substances are
not chemically combined.
. Compounds consist of
two or more elements that
are chemically combined in a fixed ratio.
Compounds
• Compounds can be classified in
several ways, including:
• acids, bases, salts
• inorganic and organic compounds.
(All organic compounds contain
carbon).
Matter can be described by its physical properties that
include, but are not limited to, shape, density solubility, odor,
melting point, boiling point, and color
• Acids make up an important group of
compounds that contain hydrogen
ions. When acids dissolve in water,
hydrogen ions (H+) are released into
the resulting solution. A base is a
substance that releases hydroxide
ions (OH–) into solution.
• pH is a measure of the hydrogen ion
concentration in a solution. The pH
scale ranges from 0–14. Solutions
with a pH lower than 7 are acidic;
solutions with a pH greater than 7
are basic. A pH of 7 is neutral.
Neutralization Equation
Kinetic Theory of Matter
Equal volumes of different
substances usually have different
masses
Matter can be described by its
chemical properties that
include, but are not limited to,
acidity, basicity, combustibility,
and reactivity (including the
ability to rust).
Atoms of the same element
are alike
The atom is the basic
building block of matter
Atoms and molecules are
perpetually in motion
Dalton
• Chemical elements are made from atoms
Thomson
• Electrons are around a positively charge
pudding like substance.
Rutherford
• The atom is mostly space, there is a
positively charged nucleus in the center.
Bohr
• The Bohr model is a model used to
describe the atom but it does not depict
the three dimensional aspect of an atom
The electron cloud model
represents our current theory of the
atom which shows that the
electrons are not in a fixed orbit but
an electron cloud
Schrödinger
Protons are positively charged, found in
the nucleus, and = the number of
electrons
• Neutrons are neutral particles and are found
in the nucleus
Electrons are negatively charged
particles found spinning around the
nucleus
Atomic Number:
• The number of
protons in an atom
determines what
element it is.
• Add or subtract even
one proton from an
atom of any element
and you no longer
have the original
element in any form.
Now you have a
different element!
• It is also the number
of electrons in a
neutral atom
• Atomic mass is the
average mass of all
the isotopes of an
element
• Neutrons can be
determined by
subtracting the
atomic mass from the
atomic number.
Atomic Structure: Isotopeshave the number of protons but
different number of neutrons
How many neutrons in the
following isotopes?
Hydrogen – 1
Helium – 4
Lithium – 6
Sodium – 22
The number of electrons in the
outermost energy level determines an
element’s chemical properties and
chemical reactivity
The information within the boxes on the periodic table can
provide you with the atomic symbol, atomic number, atomic
mass, state of matter at room temperature
The periodic table of elements is an
arrangement of elements according
to atomic numbers and properties
Metals, nonmetals, and
Metalloids
Periodic Table Basics:
Essential Question: What are Horizontal Rows called?
Answer: PERIODS
Electron Configuration
• The “Period” number
is equal to the
number of energy
levels in an atom
• Remember:
The number of
electrons are equal to
the number of
protons in a neutral
atom
What are Groups on the
Periodic Table?
Essential Question: Groups are also known as Families of Elements.
They share chemical properties. WHY?
Answer: They have the same number of valence electrons.
Electron Configuration
• For Groups IA – VIII
the group numbers
are equal to the
number of outer shell
electrons or valence
electrons
• Group “IA” has ONE
valence electron
• Group “IIA” has TWO
valence electrons;
etc.
Name that GROUP:
The Alkali Metals
IA = one outer shell
electrons
Name that GROUP:
The Alkali Earth Metals
IIA = two outer shell electrons
Name that GROUP:
The Noble Gases
VIIIA = eight outer shell electrons
(except Helium which has 2 but is
FULL)
Name that GROUP:
The HALOGENS
The Salt Formers
VIIA = SEVEN outer shell electrons
therefore Oxidation state?
-1
Name that GROUP:
The Transition Metals
3-12 usually 1 or 2 outer shell electrons
Lanthanide and actinides all have 2
valence electrons
Atoms react to form chemically stable
substances that are held together by
chemical bonds and are represented by
chemical formulas
• C + 02
CO2
To become chemically
stable, atoms lose, gain, or
share electrons
Chemical Bonding
When a metallic element reacts with a nonmetallic element, the metallic element’s atoms
gain or lose electrons forming ionic bonds
When two nonmetals react, atoms
share electrons forming covalent
molecular bonds
Metal to nonmetal ionic bond
Nonmetal to nonmetal covalent bond
Recognizing chemical
equations
• Combustion Reaction
• Organic gas and oxygen
• CH4 +
O2
CO2 +
H2O
• Combustion Reactions always have
carbon dioxide and water as products
When matter undergoes physical change,
the chemical composition of the
substances does not change.
When matter undergoes a chemical
change, different substances are formed
The Law of Conservation of Mass states that in a
chemical reaction, the starting mass of the
reactants equals the final mass of the products
A chemical equation represents the change that
takes place in a chemical reaction
• In a chemical equation, the chemical formulas of the
reactants are written on the left; an arrow indicates a
change to a new substance; and the chemical formulas of
the products are written on the right
Chemical Equations
•
•
The number of atoms on the left side of the equations
must equal the number of atoms on the right side of the
equation.
The equation must be balanced using coefficients - a
number placed in front of the molecule or atom
He
four atoms
HO
2
nine atoms
CO
2
six atoms
A subscript is the number behind the chemical symbol, it never changes.
Balancing
H2 + O2
Left side:
H2O unbalanced
Right Side
H2 + O2
Left side:
H2O balanced
Right side:
Balancing Simple
Equations
•
Aluminum + Oxygen
• Al + O2
• Left side:
•
Al + O2
• 2 Al + O2
• Left side:
•
Al + O2
• Left side:
Aluminum Oxide
Al2O3
Right side:
Al2O3
Start over…
Al2O3
Right Side:
Al2O3
Right side:
Uneven
number
must be
made
even to
balance
Chemical reactions are classified into two broad
types: ones in which energy is released
(exothermic) and ones in which energy is
absorbed (endothermic)
Nuclear reactions produce a large
amount of energy but there are
potentially negative effects of using
nuclear energy such as disposal of
nuclear waste, fission has more waste
than fusion
• Fission (I break) breaks a
radioactive nuclei into new products
and energy (Nuclear power plant
and atomic bomb)
• Fusion ( You make) takes 2 nuclei
and fuses them into one (power of
the sun and stars)
Energy exists in two states:
potential and kinetic
•
•
Potential energy is energy stored in
an object. Energy can be stored
chemically or based on position.
Kinetic energy is energy of motion.
The amount of energy depends on
the mass and velocity of the
moving object
Energy Transformations
• Energy in the form of heat is one of
the by-products of most energy
transformation
Heat and Temperature
• Heat and temperature are not the
same thing. Heat is the transfer of
thermal energy between substances
of different temperature. As thermal
energy is added, the temperature of
a substance increases.
Kinetic Energy
• Temperature is a measure of the
average kinetic energy of the
molecules of a substance.
Increased temperature means
greater average kinetic energy of the
molecules in the substance being
measured, and most substances
expand when heated.
The temperature of absolute zero (273 degrees celcius/0 Kelvin) is the
only situation where theoretically
there is no atomic/molecular
motion
The transfer of heat occurs in
three ways: conduction,
convection, and radiation
There is no change in temperature during
a phase change; only a change in
heat energy (freezing, melting,
condensing, vaporizing, sublimation)
Heat Transfers
• Heat engines
• Thermostats
• Heat pumps
• Refrigeration
Sound
• Sound is produced by vibrations and is a
type of mechanical energy. Sound travels in
compression waves and at a speed much
slower than light. It needs a medium (solid,
liquid, or gas) in which to travel.
Sound travels in compressional waves
and at a speed much slower than light
In a compressional wave, matter vibrates in the
same direction in which the wave energy travels
Sound needs a medium (solid,
liquid, or gas) in which to travel
• Sound travels
fastest in solids
• Sound travels a
little slower in
liquids
• Sound travels
slowest in gas
All waves exhibit certain
characteristics: wavelength,
frequency, and amplitude
From A to f is a wavelength or from D
to I is a wavelength
Resonance
• The natural frequency of an object.
As wavelength increases
frequency decreases
Reflection and interference
patterns are used in
ultrasonic technology,
including sonar and medical
diagnosis
Light
•
•
Light is a form of radiant energy
that moves in transverse waves
Transverse waves move at right
angles to the direction the energy
travels.
• All transverse waves exhibit certain
characteristics: wavelength, crest,
trough, frequency, and amplitude. As
wavelength increases, frequency
decreases.
There is an inverse
relationship between
frequency and wavelength
• As wavelength increases, frequency
decreases
Light travels in straight lines
until it strikes an object where
it can be reflected, absorbed,
refracted, or transmitted
• Mirrors, opaque, translucent, and
transparent materials
As light waves travel through different
media, they undergo a change in
speed that may result in refraction
(bending of the wave).
Mirror images
•
Images in convex mirrors
are always smaller
Images in concave mirrors
are always bigger (close)
Lens images
•
• Concave lens
Convex lens
Electromagnetic waves are
arranged on the electromagnetic
spectrum by wavelength
All types of electromagnetic radiation
travel at the speed of light but in
different wavelengths
Radio waves are the weakest energy and
have the longest wavelength and the
lowest frequency.
Gamma rays are the strongest energy
waves and have the shortest wavelength
and the highest frequency
•
Visible light lies between infrared and
ultraviolet waves and makes up only a
small portion of the electromagnetic
spectrum (ROY G BIV).
Several factors affect how much electricity
can flow through a system: Resistance is a
property of matter that moves against the
flow of electricity and thus some
substances are more resistant than others
Friction can cause electrons to be
transferred from one object to another.
These static charges can build up on an
object and discharge slowly or rapidly
•
•
•
Electricity can produce a magnetic field and
cause iron and steel objects to act like magnets.
Electromagnets are temporary magnets that lose
their magnetism when the electric current is
removed
The strength of an electromagnet depends on
the number of wire coils wrapped around the iron
core
Both a motor and a generator have
magnets (or electromagnets) and a coil
of wire that creates electricity
• A conductor is a material that
transfers an electric current well. An
insulator is material that does not
transfer an electric current. A
semiconductor is in-between a
conductor and an insulator.
• The diode is a semiconductor device
that acts like a one way valve to
control the flow of electricity in
electrical circuits.
• Solar cells are made of
semiconductor diodes that produce
direct current (DC) when visible light,
infrared light (IR), or ultraviolet (UV)
energy strikes them.
• Light emitting diodes (LED) emit
visible light or infrared radiation
when current passes through them.
An example is the transmitter in an
infrared TV remote or the lighting
course behind the screen in an LED
TV or notebook computer screen.
• Transistors are semiconductor
devices made from silicon, and other
semiconductors. They are used to
amplify electrical signals (in stereos,
radios, etc.) or to act like a light
switch turning the flow of electricity
on and off.
Motion
• Acceleration is the change in velocity per
unit of time.
• An object moving with constant velocity has
no acceleration.
• A decrease in velocity is negative
acceleration or deceleration.
• A distance-time graph for
acceleration is always a curve.
Objects moving with circular motion
are constantly accelerating because
direction (and hence velocity) is
constantly changing
Speed is the distance per unit
of time.
Velocity is speed in a given
direction
Newton identified three laws that
describe the motion of all objects
Newton’s First law states that an object
in motion (or at rest) will remain in
constant motion (or at rest) unless it is
acted on by an outside force
Newton’s Second law states that
force equals mass times
acceleration (F=ma)
Newton’s Third law states that for every
action force, there is an equal and
opposite reaction force
Weight is a measure of force due to
gravity on the mass of an object
Force and Motion
•
A force is a push or pull. Force is measured in
newtons. Force can cause objects to move, stop
moving, change speed, or change direction.
Speed is the change in position of an object per
unit of time. Velocity may have a positive or a
negative value depending on the direction of the
change in position, whereas speed always has a
positive value and is non-directional.
Work is the force required to move
an object over a distance
• Simple machines have different
purposes: to change the effort
needed (mechanical advantage), to
change the direction or distance to
which the force is applied, to change
the speed at which the resistance
moves, or a combination of these
• Simple machines make work easier
Work Output
•
•
The work put into a machine is
always greater than the work output
due to friction.
The ratio of work output to work
input is called efficiency
Formulas…
•
•
•
•
•
Speed = distance/time (s = d/t)
Force = mass × acceleration
(F = ma)
Work = force × distance (W = Fd)
Power = work/time (P = W/t).
Don’t you feel fabulous?
• Repeat after me…. I am as smart as a sixth
grader, I am as smart as a seventh grader, I
am as smart as an eighth grader……..
• I will do fabulous on the SOL!!!!!!!!