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

. Compounds consist of two or more elements that

are chemically combined in a fixed ratio.

Mixtures also consist of two or more substances, but the substances are

not chemically combined.

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: Isotopes- have 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 non-metallic 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 H2O CO2

four atoms nine atoms six atoms

A subscript is the number behind the chemical symbol, it never changes.

Balancing

H2 + O2 H2O unbalanced

Left side: Right Side

H2 + O2 H2O balanced

Left side: Right side:

Balancing Simple Equations

• Aluminum + Oxygen Aluminum Oxide • Al + O2 Al2O3

• Left side:              Right side:

• Al + O2 Al2O3

• 2 Al + O2 Al2O3

• Left side: Right Side:

• Al + O2 Al2O3

• Left side: Right side:

Start over… 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 Images in concave mirrors

are always smaller are always bigger (close)

Lens images

• Convex lens

• Concave 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 advantagemechanical 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!!!!!!!!