physical science – grade 8

Physical Science – Grade 8Chapters 10,11,12,18, 19

Structure of the Atom

• Matter- anything that takes up space and has mass

– Matter also has inertia

– Atoms are the smallest units of matter

Subatomic ParticlesAtoms consist of a positively charged center, or nucleus, surrounded by negatively charged particles called electrons .

The two major kinds of particles in the nucleus are protons and neutrons.

Protons are positively charged particles.Neutrons carry no charge.

Masses of subatomic particles

Subatomic particle/ charge• Proton

– positive charge (+)

• Neutron– Neutral (0 charge)

• Electron– Negative charge (-)

Mass• 1 atomic mass unit (u)

• 1 atomic mass unit (u)

• negligible

Model of the Atom

• In this model, electrons move around the nucleus in a region called the electron cloud.

• What two subatomic particles are in the nucleus? What are their charges and masses?

Electrons and Their Energy Levels Energy Level of Atom Maximum Number of Electrons

1 (K) 2

2 (L) 8

3 (M) 18

4 (N) 32

Elements and Atomic Number

• Element – A substance made up of only one type of atom

• The atomic number for each element is the number of protons.– The number of protons are = to the number of

electrons (in a neutral atom)

The Mass of an Atom• Protons + Neutrons = the Atomic Mass of the atom

• Isotopes – atoms of the same element with different numbers of neutrons

• The average atomic mass of an element is the average mass of the mixture of its isotopes

Atomic mass – Atomic number = Number of Neutrons in the atom

The Periodic Table• Elements are arranged according to increasing

atomic number

• A Chemical Symbol is a shorthand way of writing the name of the element.

The Periodic Table (continued)

Vertical columns are called Groups (1-18)– Group 18 elements are known as Noble Gases

Horizontal rows are called Periods (1– 7)

Metals, Metalloids & Nonmetals

Chapter 12

Elements and their Properties

Metals & NonmetalsMetals Nonmetals

Located on the left side of the periodic table

Located on the right side of the periodic table

Metallic Luster (Shiny)

Dull

Malleable (can be hammered and shaped)

Brittle

Ductile (can be made into a wire)

Non-ductile

Solid (except for Mercury, which is liquid @ room temperature)

Gases (except for Bromine, which is liquid @ room temperature)

High Melting Point Low Melting Point

Fewer than 3 Electrons in Outer Energy Level

More than 4 Electrons in Outer Energy Level

Coinage MetalsCopper Silver Gold

(Group 11)

Magnetic MetalsIron Cobalt Nickel

(Period 4)

Fun Fact: Did you know that the Canadian nickel can be magnetized?

(The American nickel cannot)

Metalloids• Metalloids are located on the staircase between

metals & nonmetals.

• Metalloids have properties of both metals and nonmetals.

Ex: Silicon has a metallic luster and is brittle

Boron Silicon Germanium Arsenic Antimony Tellurium Polonium

Chapter 11Chemical Bonds

Compounds

A compound is two or more elements chemically combined.

Compounds take on properties that are different than the elements that they consist of.

The compound sodium chloride (salt)

consists of the elements sodium & chlorine.

Na + Cl Sodium Chloride

Chemical Formulas• A Chemical Formula is a shorthand for the

compounds. – Subscript: Number “Written Below” that tells how

many atoms of that element are present in the compound

1. How many atoms of Hydrogen are present in this chemical formula?2. How many atoms of Oxygen are present?

Question Answer

Why do elements form compounds? They want to become chemically stable.

What is a chemically stable atom? For the atoms of most elements, the outer energy level is completely filled with 8 electrons.

Which elements are most stable? The noble gases, because their outer energy levels are full.

Are there any exceptions to the Rule of 8? Yes! Helium!(Helium has 2 electrons, but it only has 1 energy level)

Kinds of Chemical Bonds

• A chemical bond is a force that holds together the atoms in a substance.

COVALENT

Formed by the sharing of electronsMolecule- smallest part of a covalent compound

Kinds of Chemical Bonds

• A chemical bond is a force that holds together the atoms in a substance.

IONIC

Formed by the transfer of electronsProduces IonsIon- an atom with either a positive or negative charge

CHAPTER 18

WAVES AND SOUND

CHARACTERISTICS OF WAVES

• Waves- are rhythmic disturbances that carry energy through matter or space

• Medium- A material through which a wave transfers energy

• Transverse Waves – The medium moves at right angles to the direction the wave travel

Parts of a transverse wave• Crest – The highest point in a wave• Trough- the lowest point in a wave• Wavelength - the distance from one successive crest to

crest or trough to trough • Amplitude – the distance from the rest position to the

crest or the rest position to the trough

Measuring Transverse Waves

Frequency – is the number of wave crests that pass one place each second– Frequency is measured in Hertz (Hz)

Wave Velocity- how fast a wave moves forward

velocity = wavelength x frequency

V = x F

DIAGRAM OF A TRANSVERSE WAVE

Equilibrium position = Rest Position

Compressional Waves

• Compressional Wave – matter vibrates in the same direction as the wave travels

• Sound travels in compressional waves• A compressional wave is composed of a

compression and rarefaction

Comparing Transverse & Compression Waves

TRANSVERSE COMPRESSION

WAVELENGTHCrest to Crest ORTrough to Trough

1 compression + 1 rarefaction

FREQUENCY# of crests that pass a point in 1 second

# of compressions that pass a point in seconds

AMPLITUDEHeight (distance from rest position to crest or to trough)

Amount of Compression

VELOCITY V = x F V = x F

Comparing Transverse & Compressional Waves

Moving Through Media

The speed of sound waves depends on 2 things:– Medium through which waves travel– Temperature of the medium

*Types of Media:1. solids2. liquids (best conductors of sound)3. gases

Speed of Sound = 761 m/hSpeed of Light = 186,000 m/s

Which one do you think travels faster?

Decibel ScaleLoudness is the human perception of sound intensity.

-The higher the intensity and amplitude, the louder the sound.

The intensity level of a sound is measured in units called decibels (dB).

Sounds with an intensity level about 120 dB may cause pain & permanent hearing loss.

Frequency and Pitch

Pitch – the highness or lowness of a sound

The higher the frequency, the higher the pitchThe lower the frequency, the higher the pitch

The Doppler Effect is defined as the change in frequency & pitch of a sound as a result of motion.

The pitch of the emergency vehicle’s siren is higher when the vehicle is approaching because the wave crests are closer together.

Why does the sound have a lower pitch after the vehicle has passed?

Using Sound Waves!

• Ultrasonic (above 20,000 Hz)– high-frequency waves – Used in sonar (sound navigation ranging)– Medical uses

• Infrasonic (below 20 Hz)– Heavy machinery– Thunder– Body rumblings

Fun FactBats can detect sounds as high as 100,000 Hz

Music to Your Ears

Music- created using specific pitches- sound quality followed by a regular pattern

Noise- no set pattern, no definite pitch

Music… Continued• Resonance- the vibrating of an object at its natural

frequency • Sound Quality- the difference among sounds of the

same pitch and loudness

• Interference- ability of 2 or more waves to combine and form a new wave

• Reverberation- many reflections of a sound

• Acoustics- the study of sound

Chapter 19 - LIGHT

Electromagnetic Radiation

• Electromagnetic Waves are transverse waves produced by the motion of electrically charged particles

• Electromagnetic Radiation is the transfer of energy by electromagnetic waves.

- These can travel through a medium- These waves can also travel through a vacuum at

300,000 km/s (186,000 m/s)

Electromagnetic Spectrum

• Electromagnetic Spectrum- the arrangement of waves according to wavelength & frequency

• Photons- tiny, particle-like bundles of radiation

Types of RadiationRADIATION USES

Radio Waves Communication, TV, phone, medicine

Micro Waves Type of Radio Wave used in cooking

Infrared Waves Military, Police, Medicine, Heat Detection

Visible Radiation (Visible Light) Allows the human perception of objects

Ultraviolet Waves Enables Skin Cells to Produce Vitamin D, Kills Bacteria, Tanning Salons (despite negative effects)

X-Rays Medicine

Gamma Waves Cancer Treatment

Gamma Waves have the highest frequency and are the most penetrating.They can cause cancer and they can cure cancer.

Do you ever wonder….

how popcorn kernels pop so quickly in the microwave???

Light & MatterType of Material Properties

Opaque Allows no light to pass through

Transparent Allows all light to pass through

Translucent Allows some light to pass through

ColorsWhy does grass appear green?Why is the sky blue?

The color that you see is the wavelength of the colors that are reflected to your eye.

The remainder of the colors are absorbed by the object.

White = reflection of all colorsBlack = absorption of all colors

Kinds of LightingIncandescent Bulbs Fluorescent Bulbs-Produces a lot of heat

-Contains tungsten filament

- Produces light without excessive heat- Contains argon gas

Green Fact:The country is now turning over to LED Lighting, due to less

energy use and more brightness.

Properties of LightREFLECTION REFRACTION DIFFRACTION

Bouncing of light waves

Bending of light waves

Bending of waves around a barrier