Physical Science Chapter 10 PDF

Preview

Summary

Christian Draper...

Description

Chapter 10 Mechanical waves 

a disturbance traveling through a medium



they carry energy away from a source



the disturbance moves along, the material does not

Compression/Longitudinal 

Come’s from compressing molecules closer together then pulling them apart



Can travel solids, gases, and liquids

Shear/Transverse 

Comes from pulling molecules perpendicular to the bonds that exist between molecules



Requires rigid bonds



Only travels through solids

Surface Wave 

The surface moves in a circular pattern when a surface wave passes through it



A circle is a combination of compression and shear motions

Wave Characteristics 

Wavelength o Distance between wave crests



Amplitude o Amount of displacement from the rest position o Directly related to the energy carried by the wave



Frequency o Number of wave crests which pass a point per second o Sound: pitch: 20 to 20000 Hz o Light: color: 10^15 Hz

o Earthquake: 10 to 1000 Hz o Radio: set the dial: kHz to MHz 

Speed o Rate that a particular disturbance travels o Speed = frequency X wavelength o Speed is unique for the wave type and the medium the wave travels through o The speed of sound in air is 340 m/sec

Sound 

Compression wave in air



Long wavelength = low pitch



Short wavelength = high pitch



Large amplitude = loud



Small amplitude = soft

Light 

A transverse wave



Speed stays the same (speed = frequency X wavelength)



If frequency goes up, wavelength goes down



Red = long wavelength, Blue = Short wavelength

Reflection 

Waves bounce off interfaces



Ex: echo (reflected sound)

Refraction 

Waves bend when they enter a medium of different density



Speed changes

Diffraction



Waves fan out or disperse when they encounter an obstacle or opening



Amount of dispersion depends on the relatives size of the wavelength and the opening o Large when wavelength is similar to opening o Small when wavelength is much smaller than opening



Ex: sound through doorway

Interference 

The addition or subtraction of energy when two or more waves overlap



Constructive interference: Crests add to crests, troughs add to troughs



Destructive interference: Crests and troughs overlap and cancel each other out

Standing Waves 

When a wave combines back on itself by reflecting or wrapping around



Can be 1, 2, or 3 dimensional

Doppler Shift 

Wave frequency and wavelength change when the wave emitter or receiver is moving



Shorter wavelength when it comes closer



Longer wavelength when it moves away

Chapter 11 Speed of Light 

Olaus Romer in 1676 was looking for a precise celestial clock to use in navigating at sea



He timed the eclipses of Jupiter’s moons and got a different time than predicted, depending on the season



The difference was caused by the Earth’s position with respect to Jupiter



The first precise measurement was made in 1850 by Fizeau and Foucault



They found about 300,000,000 m/sec or 3X10^8 m/s



The currently accepted value is 299,792,458 m/s



1 light year = 6 trillion miles

Waves or particles 

light transports energy o it could do so as an ergy wave or as a stream of particles o we know of nothing else it does



Properties of waves o Reflect, diffract, refract, interfere



Waves diffract and interfere, particles do not

Light is an electromagnetic wave

Accelerating Electrons 

Electromagnetic radiation is giver off whenever charged particles accelerate



Causes other electrons to accelerate (TV, Microwave)

Subset of a Larger Family 

Wavelnghts of E&M radiation go from 0 to infinity



Radio (lowest energy)



Microwave



Infrared (William Herschel)



Visible (red and blue)



Ultraviolet



X-rays (Wilhelm Röntgen)



Gamma-Rays (highest energy)

Photo Electric Effect



Won Einstein the noble prize



Einstein placed electrons on a piece of metal o Tried to knockoff those electrons using light o Turned up the amplitude but nothing happened o Einstein tried a UV light and the electrons went flying off o UV light has a higher frequency the visible light

Wave Particle Duality 

Light is both a wave and a particle o It behaves like a wave when unobserved 

It travels through both slits like a wave

o It is detected like a particle 

It hits the screen as individual dots

Chapter 12 States of Matter 

Solid o Resists changes in their size and shape



Liquid o A fluid o They assume the shape of the container but do not fill the volume



Gases o Also a fluid o Expand to fill the size and volume of their container



Plasmas o A gas consisting of charged particles that are free to move

Density 

Remember this is equal to mass/volume



Unique for every material



Changes of state usually involve abrupt changes in density



Nearly all substances are more dense as solids (water is an exception)

Color 

White light contains all colors



Materials take on the color that they reflect the most



A rainbow or spectrum of all colors is called continuous



If only some portions of light are present the spectrum is called discrete or emission line



If a continuous spectrum is missing some portions of light it is called an absorption line spectrum



Each different material has a unique spectrum

Responses to Force 

Three types of force o Compression o Tension o Shear



Two types of response o Permanently deform----Plastic o Bounce Back-----Elastic

Electrical Conductivity 

Conductor o Electric current flows easily



Nonconductor o Resists flow of current (insulator)



Semiconductors o Allow current under special conditions



Ionic materials

o Nonconductors that become conductors when liquid or dissolved in water (table salt)

Chapter 13 What is a model? 

A useful analogy we can relate to



They are almost never 100% correct



Different models are used to describe the same thing at different levels of detail

Molecular Model 

All matter is made of distinct, tiny particles which are: o To small to see with an optical microscope o Different for different materials o In constant motion o Governed by newton’s laws of motion o Are indivisible



Brownian Motion o The erratic, jittery motion of a dust speck in a fluid is strong evidence supporting the molecular model

Temperature Explained 

According to this model, temperature is a measure of the average kinetic energy of the molecules o T ~ K.E. = ½ mv^2 o Hotrapidly moving o Coldslowly moving o Absolute zero no motion at all

Distribution of Molecular Speeds 

The same kind of molecules at different temperatures



Distribution of speeds increases with increasing temperature



K.E. related to temperature

Same temperature = same kinetic energy 

K.E. = ½ (molecular mass)(average speed)^2

Molecular Model Can Explain Different States of Matter 

Solids o The molecules are frozen in place but still vibrate



Liquids o The molecules move past each other but still have a weak attraction



Gases o Molecules move so fast the force from collisions is greater than gravity or mutual attractions – they fly



Plasmas o Molecules now collide so hard they break into + and – fragments. This is a breakdown of the model

Changes In State 

Temperature is molecular kinetic energy. Internal energy includes this plus electrical potential energy from how the molecules are arranged



Look at how temperature changes when changing ice into water vapor

Gas Pressure Explained 

Gas pressure is caused by molecular collisions with the walls of the container. Like throwing zillions of balls against a wall. o Remember Newton’s Third Law o The wall exerts a force on the ball o The ball exerts a force on the wall

Conduction Explained 

Low temperature = small jiggling motion



High temperature = wild jiggling motion

Evaporation Explained 

Temperature is a measure of the average speed. Some molecules go faster and some go slower. The fast ones escape as a gas even when the average temperature is below boiling.

Chapter 14 J.J. Thomson and Plasma Tubes 

Start with a neutral gas, heat it with an electrical current, and it breaks into positive and negative fragments



Negative particles are identical o Small mass; called electrons



Positive particles differ depending on gas o Large mass; called ions



Molecular model doesn’t break into positive and negative pieces

Plum Pudding Model 

Atoms consist of a thin positive fluid, which contains most of the mass, with embedded point-like negative electrons to balance the charge. o Positive “pudding” on the outside o Negative electrons throughout

Positive Fragment – ions 

The “pudding” part was hypothesized to be more massive but not very dense



It’s extent defined the atomic diameter



Positive fragments were called ions and had nearly all the mass of the original atom

Death of Plum Pudding 

Ernst Rutherford o Colleague of J.J. Thomson



Set about to find out how dense the positive pudding was by firing newly discovered alpha particles at a thin gold foil



The idea was to measure how much they deflected as they passed through

A Surprise 

As expected, most went right on through



But unexpectedly a few bounced back



Nothing in the model was dense enough to reflect alpha particles

Solar System Model 

Rutherford proposed replacing it with the “solar system” model. o The positive portion is concentrated into a tiny nucleus at the atomic center o The negative electrons orbit about the nucleus. The orbital radii define the atomic diameter instead of the positive pudding.

Problems at the start with Rutherford’s solar system model 

Accelerating (orbiting) electrons should continually radiate, loose energy, and spiral into the nucleus. We don’t see this in their spectra



However if electrons are stationary they would fall into the nucleus too



There was no fix for this. The model was created with flaws and soon died.

The Bohr Model 

The solar system model + a patch

o In the atom electrons move about the nucleus but only in very specific circular orbits 

The energy each electron has depends on its orbit o Smaller radius = less energy o Just like gravitational potential energy



To move from one orbit to another an electron must either gain or lose that exact amount of energy between the two levels



Electrons radiate when they jump to an allowed orbit of lower energy



Electrons absorb energy when they jump to a higher energy orbit

Energy and Wavelength 

Remember each wavelength of light has a specific amount of energy in its photons



Therefore transitions between orbits correspond to specific wavelengths of light

Absorption and Emission 

Comparison of emission and absorption spectra o White light passing through a gas has colors of certain wavelengths removed o That same gas when heated to high temperatures will emit photons of light of the color it absorbs

Problems with the Bohr Model 

Why are only certain orbits possible?



Why doesn’t the undisturbed atom radiate?



Why don’t the electrons fall into the nucleus?

Chapter 15 Matter Models continued 

Two puzzles remain at this point:

o The wave-particle duality of light o The physical basis for the Bohr model 

In 1923 a graduate student named Louis deBroglie proposed that moving matter also has a wave-particle duality defined from wavelength = h/(mass X speed) where h or Planck’s constant is 6 X 10^-34

Davisson-Germer Experiment 

Do a “double slit” experiment using the spaces between atoms in a crystal



An interference pattern is clearly seen. Electrons are waves

Probability 

Laws of probability predict the overall distribution of many results.



These laws do not predict what any specific result will be before it is tabulated, just the range in which it will fall

Reconciling Wave and Particle 

When we detect it, it does have a specific position but not necessarily the middle of the probability distribution



Repeat the experiment a million times and the entire curve will be filled.

Heisenberg Uncertainty Principle 

The wave nature makes it impossible to know with infinite precision how atomic matter moves



Specifically: To know a particles motion we must know its position and velocity at the same time



But how do you locate the position of a wave/particle electron



Electrons: fuzzy position and fuzzy wave properties



The uncertainty in position times the uncertainty in momentum (mass X velocity) is greater than Planck’s constant

Important Tie-in to atoms 

An electron orbiting a nucleus has its position determined to within the diameter of the atom



But its momentum is therefore made so uncertain we CANNOT know how it orbits

Chapter 16 Standing Waves 

These are standing waves created using a jigsaw and a stretching band



Why do we get a standing wave? Where are the nodes?

2 Dimensions 

It is easy to create standing waves in 2 dimensions

Wrap standing waves around a point 

These are patterns or orbitals



Examples o One wave o Two waves o Three waves

But it turned out to describe what we observe 

De Broglie’s idea explained the Bohr orbitals



The quantized orbits of the Bohr model are predicted perfectly by requiring electrons to exactly wrap 1, 2, 3, etc. waves around the nucleus

The Quantum Model of the Atom 

Electrons are found in 3-D electron probability waves surrounding the nucleus



They do not orbit

o Exist trapped in the locations given by standing wave clouds o Wave clouds = orbitals 

Do not orbit like a planet

Three Dimensional Atomic Orbitals 

The shape and energies of the actual orbitals depend on the number of standing waves in the pattern. The are found from solving the Shrödinger Wave Equation

Orbital Patterns 

One wave – first level: o Electrons will resonate in one pattern, called an “s” orbital



Two waves – second level: o Electrons will resonate in two patterns, “s” and “p” orbitals.



Three waves – third level: o Electrons will resonate in “s”, “p” and “d” orbitals

S orbitals 

All numbers of standing waves have “s” orbitals



They are all round but their interiors are different



Still, in each case there is just one orbital

Orbital Patterns 

The pattern continues on as s, p, d, f, g, h, I, j, etc.



Each new orbital set has two more orbitals than the previous one

The Pauli Exclusion Principle 

At most two electrons can occupy the same orbital. If two electrons are in the same orbital, they must have different spins

Absorption line spectra revisited



The outer electron of any atom can jump up to higher orbitals creating a unique absorption spectrum for that element

Emission line spectra revisited 

It can then fall down creating the emission spectrum for that element

Chapter 17 Designating a Specific Atom Reading the Periodic Table 

Atomic number = number of protons



Mass number = number of protons and neutrons



Ionic State = total charge of atom = number of extra or missing electrons. If they are missing the number is positive. If there are extras the number is negative

Elements 

I can take two substances that are very different, and get the exact same elements o Example (rust, magnetite)



Substances that would not break down further were called elements o Example (Fe and O)

Law of Constant Composition 

Early Chemists discovered that certain substances always broke down into the same ratios of the same materials. “Laws of Constant Mass” and “Laws of Constant composition”

Mendeleev found periodicity in the behavior of elements 

Dmitri Mendeleev o Father of the periodic table



Ordered the elements of atomic weight (mass number)

o Established that there were re-occurring patterns in the ways that elements combined with other elements 

Order the elements by atomic number and you get a periodicity

Chemical Families or Groups: Alkalai Metals 

At the left of the periodic table are the alkalai metals: o Lithium (Li), Sodium (Na), Potassium (K), etc.



All react energetically with water

Halogens 

The second column f...