section a1: physical properties we characterize atoms or matter according to a couple of different...
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Section A1: Physical Properties
We characterize atoms or matter according to a couple of different properties
1. Physical Property: A characteristic we can measure without changing the substance under examination
• eg: Temperature, mass, density, melting point2. Chemical Property: The ability of a substance
to change into another substance• eg: Hydrogen gas has the chemical property of
reacting with oxygen to make water
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Physical Properties
• When we measure a physical property, we report the results in a standardized format– SI (Systeme Internacional) units will always be
used in this class
• Let’s look at the Physical Property: Mass
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Mass
• A lump of iron has a mass of 15 kg• Originally, a gram was defined as:
“The absolute weight of pure water equal to the cube of the hundredth pat of a meter and at the temperature of melting ice (4° C)”
• Hmmm. That’s not very handy.
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Mass
• It is now defined as on thousandth of a kilogram (the SI unit of mass)– In Sevres, France, there is a block of
platinum/iridium alloy that is the standard mass of 1 kilogram
– All other 1kg blocks in the world come from this mass template.
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SI Units and the Metric SystemYou must memorize these!
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Working with units
• DO NOT GET CARELESS…EVER!– Always keep track of your units
• I will take points off of anything you give me if you leave the units off
• I will stare at you when you give me an answer without units until you put them in your answer
• IT REALLY IS THAT IMPORTANT!!!!
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Dimensional Analysis
• You will frequently have to convert between units during your life (Yes, your entire life!)
• To do this, we will need to employ DIMENSIONAL ANALYSIS
• Step 1: What do you have? What do you need?
• Step 2: What is the conversion factor?• Step 3: Setup a calculation that cancels your
given units and puts your target units on top.
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Dimensional Analysis: Example
• How many centimeters are in 29 inches?
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Dimensional Analysis: Example
• How many ounces are in 750 kg?
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Dimensional Analysis: Example
• A sample of an alloy has a density of 7.9 kg/cm3. What is the density in kg/m3?
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Properties dependent upon the mass of the sample
• Intensive property: A property that is independent of the mass of the sample
• Extensive property: A property that depends in the mass of the sample.
Temperature is an ________ property
Volume is an ________ property
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Density
• The density of a sample is an intensive property that is calculated by dividing on extensive property (mass) by another extensive property (volume)
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What does density really tell us?
• How tightly packed the atoms are in a given space.
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Significant Figures
• Simple rule for my class: Take the value with the lowest number of significant figures and report your answer that way.
• See the rules in Appendix 1C of your text.– I won’t kill you on this (but I might just hurt you a little bit)
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Accuracy and Precision
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A.2: Force
• Force is defined as an influence that changes the state of motion of an object
• Newton’s Second Law:– An object experiencing a force undergoes an
acceleration
Force acceleration
F a– The proportionality constant is mass
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Force and Acceleration
• You flick a marble with your finger. What happens?
• You flick a bowling ball with your finger. What happens?
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A.3: Energy
• Energy is the key to everything:Shape, motion, chemical reactions, color,
sound
• But what is it really?
• We will define energy as the capacity to do work.– Work is defined as motion against an
opposing force
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Energy: Examples
• Energy is required to lift a book from the floor
• Energy is required to move electrons through a wire
• Energy is required for your cells to import glucose (to make more energy!)
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The SI unit of energy is the joule (J)
Defined as “the work done by a 1 Newton force in moving an object 1 meter”
A Newton is defined as "the force necessary to accelerate a 1 kg object at 1 meter per second per second”
Multiplying the Force times the distance it is exerted (1 m)
gives the units of a Joule as kg m2/s2
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Types of energy
• There are three types of energy:1. Kinetic energy: Energy associated with
motion
2. Potential Energy: Energy related to position
3. Electromagnetic Energy: The energy of an electromagnetic field
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Law of Conservation of Energy
• The total energy of a particle is the sum of its kinetic and potential energies
• Energy can neither be created nor destroyed
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B: Elements and Atoms
• Approximately 5000 years ago, philosophers wondered what would happen if they cut matter down into ever smaller bits– Like those Matryoshka dolls
• What is the smallest point they could reach before whatever they were cutting was no longer recognizable as the starting material
• The word “atom” comes from the Greek words “atomos” which means not divisible
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Dalton and the Concept of the Atom
• In 1807, John Dalton looked at many different compounds ands determined that they had regular patterns
• Water had 8g of oxygen for every 1g of hydrogen
• Hydrogen peroxide had 16g of oxygen for every 1g of hydrogen
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Dalton’s Atomic Hypothesis
1. All atoms of a particular element are identical
2. Atoms of different elements have different masses
3. A compound is a specific combination of atoms of more than one element
4. In a chemical reaction, atoms are neither created nor destroyed; they exchange partners to produce new substances
These tenets were first proposed 202 years ago and they are all true!
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All matter is made up of various
combinations of the simple forms of
matter called the Chemical Elements. An
element is a substance that consists of
only one kind of atom.
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The Nuclear Model of the AtomFirst proposed by Rutherford based upon his alpha particle experiment in 1911
Helped to explain his observation that 99% of alpha particles passed through gold foil without hitting anything
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Atomic Number
• The Atomic Number, Z, of an element is the number of protons in the nucleus.
Hydrogen: Z=1, therefore it has _ protons
Oxygen: Z=8, therefore it has _ protons
Cesium: Z=55, therefore it has _ protons
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Mass of an Atom
• Using mass spectrometers (we’ll discuss later), we have determined the mass of individual atoms of most elements.– We can use the values to determine how
many atoms are in a sample.
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Isotopes
• Mass spectrometers also allowed us to observe that every element had a couple of different masses in the sample.
• This observation led to the discovery of chargeless particles in the nucleus called neutrons
• Except for the lack of charge, neutrons and protons are nearly identical.
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• The sum of the number of protons and neutrons is the Mass Number, A, of the atom.
• Example: Neon
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Examples: Atomic and Mass Numbers
• How many protons, neutrons and electrons are in a sample of Oxygen-18?
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The Organization of the Elements
• As of today, there are 117 known elements– Some are manmade, with Technetium
created in 1937.– Some exist for a few microseconds.
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The Periodic Table
• In 1869, Dmitri Mendeleev discovered that the elements show PERIODIC trends in properties.– He organized the elements based upon
these observations and today, we have the…
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The Periodic Table
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Metals, Nonmetals and Metalloids
• Most elements are solid at room temperature and pressure– 11 are gases (N, O, Fl, Cl, H, Noble gases)– 2 are liquid (Br, Hg)
• Metals: Conduct electricity, are malleable and ductile
• Non-metals: Do not conduct electricity, are not malleable or ductile
• Metalloids: Have some physical properties of metals, but behave chemically as a non-metal