Take simple review notes in book not
copying the entire PPT
Will be on Mr. K’s sharepoint site for
review and study tonight!
Engage
Hydrogen POWer
Paragraph 2:
Chemical reactions involve inputs and outputs (also called
products and reactants).
When a chemical reaction occurs, the new chemicals created
have different properties than the original chemicals.
An example is when a candle burns. A candle is made of
paraffin. When it is burned, it uses up oxygen, and produces
carbon dioxide and water. The properties of paraffin and
oxygen (inputs) are very different than the properties of carbon
dioxide and water (outputs).
Another example is when you mix salt and water. Saltwater
(output) is very different than either salt alone or pure water.
Paragraph 3:
Conservation of matter means that matter is neither created
nor destroyed…it just changes form.
For example, when I mix salt and water, the salt seems to
disappear. But the sodium and chloride atoms are still present,
just in a different form.
Energy is also present and it changes form, too. Some
reactions break chemical bonds apart. In this case, the energy
is used to form the new chemicals, or released as heat or light
or sound.
Explore
You already know quite a bit about density.
Density = mass/volume
Materials with lower density ‘float’ on top
of materials with greater density. This is
true
in liquids
in solids
& in gases
Examples:
Helium balloons float in air.
Hydrogen filled zeppelins (the Hindenburg) float in air.
*Helium and Hydrogen are both gases that are less dense
than air when all are at the same temperature and pressure.
1) Can you think of any gases that are more dense than air?
2) What is wrong with the phrase:
“can you think of any gases that are heavier than air?”
Your turn:
the density of air vs. Carbon Dioxide
Remember that dry ice is frozen carbon-dioxide. It goes
directly from it’s solid (frozen) state into a gaseous (vapor)
state. This is called sublimation.
Dry ice sublimates at −78.5 °C (−109.3 °F) at atmospheric
pressure. In other words, if dry ice exists as a solid, it is at
LEAST minus-109.3 °F . This extreme cold makes the solid
dangerous to handle without protection due to burns caused
by freezing (frostbite).
Compare this to water ice, which melts at positive-32 °F.
In other words… don’t touch the stuff!
The Periodic Table
& Molecular Masses:
The atomic mass is the total mass of protons, neutrons and electrons in a
single atom. It is usually expressed in units called atomic mass units (amu).
The Periodic Table
& Molecular Masses:
Examples:
NaCl
Na =
Cl =
NaCl =
H2O
H=
O=
H2O =
Your Turn
CH4
C=
H =
CH4 =
CO2
C=
O=
CO2 =
NO (~air)
N=
O=
NO
Using this information, which bubbles should float in air, and which should sink???
The Periodic Table
& Molecular Masses:
Density Layers in stars indicate the
presence of several elements…
Explain
But first… Remember 5 important points:
1) Protons and neutrons have roughly the same mass.
2) Electrons are relatively light compared to protons and
neutrons (it takes about 1836 electrons to equal the mass
of a single proton).
3) The atomic number tells us how many protons are in an
atom.
4) An atom that is “electrically neutral” has the SAME
number of electrons as it has protons.
5) The number of PROTONS determines the type of element.
Several Isotopes of Selenium
Notice they can have different colors and textures!
But first… Remember 3 important points:
1) An atom does NOT have to have an equivalent number of
neutrons for each proton.
2) The number of NEUTRONS determines the “flavor” of
element… called an ISOTOPE.
3)
We can determine the number of neutrons by looking at the
atomic mass and the atomic number of an element:
For instance, carbon has an atomic number of 6. This means
it has SIX protons. It also has an average atomic weight of
12.0107. This means it’s average weight is 12 “ amu”. Which
implies that carbon has about 6 neutrons on average.
Summary, p. 1/3
Hydrogen is the lightest element.
Astronomers have determined that stars have elements other than just
hydrogen.
H is used in nuclear reactions to make new elements (with different properties!)
Helium is next most common.
The energy released by stars is a result of nuclear reactions.
Stars are NOT big bonfires, like a planet on fire! They are a ball of gas, held
together by gravity and releasing energy because of all the nuclear reactions
occurring. If they were really “on fire”, they would need a lot of oxygen. Check
out the table on the next page to see how much oxygen there is in our Sun…
Summary, p. 2/3
Here is a table of the 10 most common elements in our Sun:
Abundance
(% of total
number of atoms)
Abundance
(% of total
mass)
Hydrogen
91.2
71.0
Helium
8.7
27.1
Oxygen
0.078
0.97
Carbon
0.043
0.40
Nitrogen
0.0088
0.096
Silicon
0.0045
0.099
Magnesium
0.0038
0.076
Neon
0.0035
0.058
Iron
0.030
0.014
Sulfur
0.015
0.040
Element
Charges Must be Balanced Too!
Take-home message:
A positive charge plus a negative charge = neutral charge.
In the high-energy environment of the stars, protons and
electrons can combine!
Isotopes: Nuclear Symbols
Take-home message:
The # of electrons = # protons in a neutrally charged atom.
Chemical reactions involve electrons, and do not depend
upon the number of neutrons.
So, the chemical properties of isotopes are the same.
So, carbon-13 reacts chemically the same way that carbon14 reacts. But carbon-14 is still heavier.
These “isotope symbols” are most often called
“Nuclear Symbols”.
Isotopes Day 3: Nuclear Symbols
Explain
Star Power
My Notes: Fusion
pages 223-225
1) Fusion reactions fuel stars.
2) The carbon on Earth comes from those fusion reactions in the
stars.
3) Centers of stars can be 10 million degrees Celsius. A candle, by
comparison, is about 400 degrees Celsius.
4) Four Hydrogen protons fuse to make one helium. Two of the
protons from the hydrogen atoms join with 2 electrons and
become 2 neutrons. So, ONLY 1 helium atoms are formed and
the additional neutrinos are emitted along with a lot of energy!
5) Some mass is converted into energy.
6) For example, 454 g of hydrogen fuses to make only 451 g of
helium. The “lost” 3 grams (1%) is converted into energy… like
heat and light from the sun.
Continued, next slide…
My Notes: Fusion
pages 223-225
7) The strong force holds protons and neutrons together.
8) The electrostatic force is the force between electrons and
protons. It is not as powerful as the Strong force. Scientists
know it is weaker because the electrostatic force is responsible
for chemical reactions, which require less energy than nuclear
reactions (influenced by the strong force).
My Notes: Radioactive Decay
pages 225 - 227
1) Fusion is not the only way nature alters a nucleus.
2) Some nuclei break apart on their own. This is called radioactive
decay.
3) An alpha particle is a helium nucleus, with 2 protons and 2
neutrons.
4) Charge is conserved, and mass numbers are the same.
5) Beta and gamma particles are also types of radioactive decay
particles.
6) All radioactive decay processes are random… you cannot tell
exactly which particle will decay at any given moment. But you
can tell the RATE of decay of a group of particles.
Continued on next slide…
My Notes: Radioactive Decay
pages 225 - 227
7) The half-life is unique to each type of particle. It tells us how
much radioactive material will be present at a given time. For
instance, it 100 g sample of Iodine-131 has a half-life of 8 days,
then after 8 day there will be 50 grams left.
8) Half-lives vary from 4.5 billion years for Uranium-238 to just
fractions of a second for some elements such as most isotopes
of gold
(
My Notes: Fission
pages 228 - 229
1)
2)
3)
4)
5)
6)
Fusion involves putting nuclei together.
Fission involves taking nuclei apart.
Both involve changing the nuclei.
In fission, nuclei split into approximately equal parts.
Nuclear power plants use fission reactions to produce energy.
Sample reaction:
Notice that the mass numbers (top boxes) equal the same numbers
on the left as on the right side. The mass is conserved.
Notice that the atomic numbers also balance in fission reactions.
Continued on next slide…
My Notes: Fission
pages 228 - 229
7) Chain reactions in power plants occur when a reactant collides
with another particle, causing a 2nd fission, etc.
8) The minimum amount of material needed to produce an atomic
explosion is called the critical mass. For some bombs, it only
takes about 45 lbs of material to set off an atomic bomb.
9) Controlled fission does not explode.
10) Water coolants surrounding the material also absorb some of
the extra neutrons.
11) Energy from the fission is used to boil water, which turns
turbines and produce electricity.
12) Some of the products are radioactive isotopes with very long
half-lives; they last a long time. They are difficult to dispose of
safely. We currently bury them in containers.
My Stop & Think Answers: Fission(p. 229)
1) Fission and fusion are alike because:
* both involve nuclei changing
* both require fast moving particles to collide
* both involve the conversion of matter into energy
2) Fission and fusion differ in the following ways:
* fusion involves combining two or more nuclei into larger, more
massive nucleus; fission breaks up a nucleus into 2 smaller nuclei or 1
smaller nucleus & other particles.
* fusion powers the Sun; fission does not!
3)
Continued on next slide……
My Stop & Think Answers: Fission(p. 229)
4) Fusion reactions in stars are not necessarily chain reactions, as they are
in nuclear power plants.
In power plants, humans initiate a chain reaction by getting one particle
to fuse with another. Then the reactant produces a particle that
subsequently initiates the next reaction [kind of like in billiards when
one ball hits several other balls, then they all go off hitting even
more]. This occurs until the reactant concentrations become very
small or zero.
In stars, the fusion products might go off and initiate it’s own chain, but
there is so much energy in a star that thousands of fusion reactions
are starting spontaneously. Many of these reactants are involved in
other nuclear processes, not just the “chain” of fusion events.
5) 72 days = 3 half lives. So, we start with 100 grams, then “half” it three
times: 100  50  25  12.5 grams of Thorium remaining.