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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.
IONIC COVALENT
Formed by the transfer of electronsProduces Ions
Formed by the sharing of electrons
Ion- an atom with either a positive or negative charge
Molecule- smallest part of a covalent compound
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
• Transverse Waves – The medium moves at right angles to the direction the wave travels
• 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:solids, liquids (best conductors of sound)gases
Speed of Sound = 761 m/hSpeed of Light = 186,000 m/s
Which one do you think travels faster?
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
Decibel Scale
Loudness is the human perception of sound intensity.
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.
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?
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
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