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[♪ introductory music]
(water droplets)
[♪]
♪ Simply Science
Turning all of these parts into a high tech mountain bike is a bit of a puzzle.
But at least I know what it's supposed to look like when I'm finished.
Imagine getting boxes of parts and having no idea
what the finished product was going to be.
Now there's a challenge.
[♪ music]
Early scientists didn't have an easy job.
They were trying to make sense of mountains of spare parts
in the form of observational evidence.
Nobody knew the structure of the atom or the periodic table,
so they started by asking some good questions:
What's the significance of patterns among the elements?
Can the theory of the atom explain the organization of the periodic table?
and, what does the periodic table allow us to predict
about the elements and chemical reactions?
Questions like these are simply the nuts and bolts of science.
[♪ music]
Sarah: The first part of the puzzle was to find patterns
among the elements and arrange them in a logical way.
In 1864, a scientist named John Newlands stated the periodic law:
♪ Science rules.
♪
Sarah: [reading]
Julien: In 1872,
Dmitri Mendeleev organized the known elements into the first usable periodic table.
Laureen: It works like this:
Elements are listed from left to right,
in order of increasing atomic mass relative to hydrogen.
Julien: But Mendeleev breaks them into a new row when chemical properties repeat.
Laureen: Like sodium and potassium for instance.
Julien: Yeah, they have similar physical and chemical properties
so they belong to a vertical group of similar elements.
Laureen: And since properties repeat periodically,
we call this the Periodic Table.
Male narrator: Mendeleev's table had gaps in it,
and he predicted that these were unknown elements.
One of these elements he called "eka-silicon."
So when elements like Germanium,
which follow Silicon,
were discovered and matched the properties Mendeleev predicted,
he became famous.
Mendeleev had found patterns among the elements,
but at the time,
nobody could explain the big picture.
[♪ music]
By the early 1900s,
Scientists had found a critical part of the puzzle:
the nuclear model of the atom.
[♪ music]
Male narrator: Ernest Rutherford discovered that the atom had a tiny nucleus
containing positively charged protons
with an equal number of negatively charged electrons orbiting around it.
Most of the atom was empty space,
but the tiny nucleus had a huge mass.
According to Rutherford's calculations,
the nucleus of the atom was about one-ten-thousandth
of the total size of the atom.
Female narrator: Soon after,
a student of Rutherford's,
H. G. J. Moseley,
demonstrated that as we move from one element
to the next in Mendeleev's table,
the positive charge in the nucleus generally increases by one unit.
He called this the "atomic number,"
the number of protons contained in the nucleus.
That solved the problem of some elements not lining up with their families
when they were ordered according to increasing atomic mass.
And that's why we now order the elements
using atomic number instead of relative atomic mass.
[♪ music]
Where protons couldn't account for the total mass of the atom
and electrons have practically no mass at all,
so Rutherford predicted, and James Chadwick proved,
that neutrons also exist in the nucleus.
These are heavy, neutrally charged particles
that account for the missing mass.
By scientific convention,
the mass of a proton, or a neutron,
is defined as one-twelfth the mass of a carbon-12 atom.
This is called an "amu,"
an atomic mass unit.
The total mass of an atom is the sum of the amu
of all the protons and neutrons in the nucleus.
[♪ music]
Julien: [reading]
Sarah: the number of protons in the atom of an element is constant
but the number of neutrons can vary.
The atoms of elements with variations in the number of neutrons are called isotopes.
Sarah: Carbon, in its most common form,
has six protons and six neutrons in the nucleus.
so we call it carbon-12.
But there are also less common carbon isotopes
with one or two extra neutrons.
called carbon-13 and carbon-14.
Isotopes like these have variations in their mass.
because of the extra neutrons.
[♪ music]
Julien: [reading the above text]
In spite of all of these discoveries,
the atomic models couldn't explain why elements had repeating chemical properties.
There was still work to be done.
♪
Mountain bikers are looking for very light-weight bikes.
They want to be able to ride their bikes fast,
and they want to be able to get up hills fast
so the lighter the bike, the faster they'll go.
The materials the industry is using right now are:
chromoly,
aluminum and carbon fibre.
and chromoly being the most popular.
Chromoly is a type of steel.
It's quiet a bit stronger than steel--
It's about ten times stronger than steel
and it's also much lighter.
so they use chromoly because it's also cheaper than using aluminum or carbon fibre.
If you're riding one of our chromoly bikes,
they weight in at between twenty-seven pounds
and as light as twenty-five pounds... twenty-four pounds...
That's very light for a chromoly bike.
The aluminum bikes weight from twenty-four to twenty-six pounds
and the carbon fibre bikes can weigh as little as eighteen pounds
[♪ transition music]
In 1913,
a scientist named Niels Bohr put together a number of existing ideas
in a totally new way.
Now, the Bohr model of atomic structure
was the first to explain reactivity
and periodicity on the periodic table.
It's all about the interaction.
of energy,
and electrons.
Julien: Bohr's model of electrons shows us that electrons exist
in specific orbits or energy levels.
Laureen: The electrons in the outer level have the most energy.
If that other level is filled,
the atom is stable.
Julien: If the outer level isn't filled,
then the atom is reactive,
because it's trying to reach a stable state.
Bohr made use of the theory that energy exists
in tiny packets.
Each small bundle of energy is called a quantum.
If an electron absorbs a quantum of energy,
it could move to a higher orbit--
a higher energy level.
If it releases a quantum of energy
it can move to a lower energy level.
Bohr also found that the first three orbits around the nucleus
contain two...
eight...
and eight electrons.
Electrons in the highest energy level,
farthest away from the nucelus,
are invovled in chemical reactions and bonding.
Julien: We call these valence electrons.
♪ Science Rules.
Sarah: In chemical reactions,
metals are electron donors.
They try to give away all valence electrons
to get to a stable state--
a completed inner-level.
Non-metals are electron acceptors.
They try to gain extra velence electrons to fill their outer-level
and reach a stable state.
When chemicals react,
existing bonds are broken and new ones are formed.
But what are the different kinds of chemical bonds?
Sodium chloride (table salt) is an example of a compound
which exhibits an ionic bond.
Laureen: Metallic and non-metallic atoms combine
by transferring valence electrons.
We call these ionic bonds.
Julien: By transferring electrons,
both atoms end up with a full outer level,
which makes them stable.
And, as a result,
the two atoms are changed to ions which have opposite charges.
Metals form positively charged ions
and non-metals form negatively charged ions.
Julien: Opposite charges attract,
so the ions are attracted to one another.
Laureen: We call the result an ionic compound.
♪
Male narrator: Sulfur dioxide is an industrial emission linked to acid rain.
It's an example a compound exhibiting a covalent bond.
Laureen: Non-metallic atoms combine by sharing the valence electrons.
We call these covalent bonds.
Julien: By sharing electrons,
the atoms manage to fill their outer levels to become more stable.
Laureen: The result is a molecular compound.
In this case, it's sulfur dioxide.
[♪ fast paced industrial rock music]
♪
Laureen: What makes some metals strong, like steel,
and some not so strong, like copper?
Len Thompson: Typically that metal's properties are based on the microstructure of the steel
which we can see at the microscopic level.
Materials like iron and copper are pure metals
and they have a continuous, uniform type of structure.
Alloys are a little bit different.
They have a discontinuous type of structure
Steel for example, is a mixture of iron and carbon.
The carbon forms its carbides and we get hard, brittle material here
mixed in with the continuous structure of steel
which increases the strength and hardness of the steel.
Karen: How are alloys like that used?
Len: Typically they are used based on their properties.
If we look at a stainless steel application in your kitchen for example,
a kitchen sink is made of stainless steel for its corrosion resistance.
Also, a butcher knife blade is made from stainless steel.
for corrosion resistance.
The difference between the two is the kitchen sink
material must be relatively soft and ductile
so it can be formed or pressed out of a single plate.
while a butcher knife blade must be very hard and
resistance to maintain its sharpness after several uses.
[♪ transition music]
Male: Using Bohr's model of the atom,
we can figure out the structure of the elements
and that helps explain why the periodic table works.
Sarah: Let's compare Mendeleev's table with this modern periodic table.
What are some similarities and differences?
Julien: They both organize the elements into vertical groups and horizontal periods.
Sarah: That's true...
Laureen: The elements in the modern table are listed from
left to right in order of their atomic number,
the number of protons in the nucleus.
Julien: That is the change.
Sarah: Right, Mendeleev used relative atomic mass.
Julien: The order of the elements is not that different--
at least in some periods.
Laureen: Yeah, for example, look at period two:
lithium, beryllium, boron, carbon,
nitrogen, oxygen, and fluorine.
It's a perfect match for the modern table.
Julien: Except for neon, which hadn't been discovered yet.
Sarah: Right, a lot of elements weren't known when Mendeleev was doing his work.
[♪ music]
Laureen: The periods on both tables break in the same places.
the chemical properties of the elements repeat.
Julien: There are groups of elements with similar chemical properties.
Sarah: How well do the groups match up?
Laureen: Pretty good...
For instance, this group right here--
fluorine, chlorine, bromine,
iodine, and astatine.
Julien: Mendeleev has fluorine, chlorine,
bromine,
and iodine in the group.
Sarah: And astatine wasn't known at the time.
Laureen: Here's a major difference:
These items here, metals, like iron and copper,
are in the middle of the modern table.
Julien: And another thing--
why are these two rows underneath the main table?
[♪ music]
Sarah: On the modern periodic table,
every element is sequenced by its atomic number.
That puts the shaded, metallic elements from Mendeleev's table
into the center of the modern periodic table.
These are called the transition elements.
Other sections in groups have special names as well.
The elements at both sides of the table are called representative elements
because they follow the periodic law very closely.
These include alkali metals,
alkaline earth metals,
the halogens,
and the noble gases.
These two extra rows at the bottom are the lanthanides
and actinides.
They've only been moved out of the table for convenience,
so they can fit the entire table on a single page.
[♪ music]
Laureen: Another thing we notice is that Mendeleev's table
doesn't have a neat dividing line
between metals and non-metals.
Julien: But in this modern table,
the elements on the left-hand side
are metals.
And the elements on the right-hand side, here,
are non-metals.
Sarah: Good observation.
Sarah: The line dividing metals and non-metals in the modern periodic table
is called the "staircase line" because of its shape.
Note that metalloids straddle the staircase line.
Sarah: One thing the Bohr model allows us to do is draw models of individual atoms.
How would you draw an atom of argon?
Laureen: Well we know argon is a noble gas
Sarah: Which means the outer level is filled.
Julien: And its atomic number is 18,
which means it has 18 protons as well as 18 electrons.
Sarah: And 18 or more neutrons depending on the isotope.
Julien: The nucleus has 18 protons
as well as 18 or more neutrons.
Laureen: And electrons in levels two,
eight,
and eight,
adding up to eighteen.
Sarah: Right, now how did the energy levels of the electrons
fit in with argon's position on the periodic table?
Julien: Well, three energy levels.
Laureen: It's in row three, so that means it's in period three.
Julien: So, the period tells us how many energy levels each element has.
Sarah: You got it. Bohr's model explains why the elements break into periods,
because of the number of occupied energy levels they have.
Laureen: So lithium would have two energy levels.
That's why it's in period two.
Julien: And iodine fits into period five
which means it has five energy levels.
Sarah: Right, that's how it works.
[♪ music]
Female: These multivitamins contain elements from the periodic table...
calcium, iron, potassium...
Why is that?
Alyson: Some of the elements that you may find on the periodic table
are also responsible for helping us maintain good health.
It's best to follow a good, healthy way of eating to get all your nutrients.
You can also get them from supplements such as multivitamin and mineral pills.
So which are the most important minerals for our bodies?
Iron is crucial.
It sits in the middle of our red blood cells and helps us transport oxygen throughout our bodies.
People who don't take in enough iron tend to get iron-deficiency anemia.
Younger people who don't take in enough iron may get attention deficit disorder.
Calcium is also a very important mineral.
As you would guess, it helps us with the structure of our bones and teeth.
But a small percentage is responsible for the contraction of muscle.
People who don't take in enough calcium may get weaker bones as they get older.
That's called osteoporosis.
What about potassium?
Alyson: Potassium and sodium are responsible for the transmission of nerve impulses
and magnesium helps us absorb calcium better.
Should I start taking multivitamins to make sure I get all the minerals I need?
Alyson: It's best to follow a healthy way of eating such as outlined by the Canada Food Guide.
And there still needs to be research before we start recommending micronutrients such as copper and selenium.
But even those are found in a healthy diet.
[♪ music]
When we go from Mendeleev's table to the modern table
we're seeing the discoveries and refinements
that have been made over the last hundred years or so
and Bohr's model helps explain why it works.
[♪ transition music]
The periodic table puts centuries of theoretical ideas and experimental data at your fingertips.
It allows you to make predictions about the elements
and how they react with each other.
Sarah: On the periodic table,
metals become increasingly reactive as they go down and left.
Non-metals become increasingly reactive as we go up and right.
Except at the extreme right where we find the noble gases.
The valence electrons of an element determine its chemical behavior.
You can find the number of valence electrons for any representative element
by the position of its group on the table.
Noble gasses have full outer levels.
Think of them as zero.
For metals, count from the left,
adding one per group to find out how many extra valence electrons the metal has to give away.
For non-metals,
count from right to left.
Noble gases being zero,
to find out the number of valence electrons the element needs to fill in its energy level.
[♪]
Julien: [reading the above text]
Laureen: We've got two sets of representative elements:
magnesium and oxygen
and carbon and chlorine.
Julien: What kind of reactions can we predict for each set using the periodic table of elements?
[♪]
Julien: First, magnesium and oxygen.
Laureen: Magnesium is a metallic element.
When we look on the periodic table, we find that it's somewhat reactive.
Julien: And coming from the left side, it has to give away two valence electrons.
Laureen: We're using an energy level diagram to show why.
Magnesium's atomic number is twelve.
That means it has twelve protons and twelve electrons.
Julien: It has two electrons on its first level,
the second level has eight,
and the third level has two.
twelve electrons all together.
Laureen: So it needs to get rid of these two other electrons.
Julien: Right, to become stable.
Laureen: Then there is oxygen which is a non-metallic element.
Julien: From its position here on the table
we can see that it's probably quite reactive.
And counting from right to left, it needs two electrons.
Laureen: Here's why:
Oxygen's atomic number is eight.
So that means it has two electrons in its first level,
and six electrons in it's second.
Julien: It needs two electrons to fill its outer level.
Laureen: So when these two elements react,
an ionic bond will form.
Julien: One atom from each element is needed for a stable state.
Laureen: Magnesium oxide: MgO.
[♪]
Julien: Second, there's carbon and chlorine.
Laureen: Carbon is on the non-metal side of the table.
It's position here shows it has four valence electrons.
Julien: The energy level diagram for the carbon atom shows us why.
Laureen: It's atomic number is six,
that means it has six electrons,
six protons,
It's first energy level has two electrons,
and it's second has four.
Julien: So it'll share four of it's own electrons
to get four more and fill the second level.
Laureen: Chlorine is a non-metal, too.
From its position here on the table,
we see that it needs one valence electron to fill its outer energy level.
Its atomic number is 17
which means it has two electrons in its first level,
eight in its second,
and seven in its third.
That's 17 .
Julien: So it'll share one of its electrons to get one electron back,
and fill the third level.
Laureen: We predict a covalent bond.
Julien: With every four atoms of chlorine bonding with every one atom of carbon.
Laureen: That should give us carbon tetrachloride,
CCL4, a molecular compound,
Sarah: ... Which is a nonpolar solvent used to prepare other carbon compounds.
Nice job with your chemical predictions!
Julien: If you apply the rules it isn't too hard.
Sarah: That's true,
but it's important to recognize
that we've been applying the simplest rules of chemical behavior.
Laureen: So, there are other possibilities?
Sarah: Absolutely.
Chemical reactions can be very complex.
Many elements, under the appropriate conditions,
can combine in different proportions.
Julien: Like what?
For example,
carbon plus oxygen can react to form carbon dioxide...
or carbon monoxide.
Sarah: Carbon can also combine to form the most fantastic and complex organic molecules...
from sucrose,
to gasoline.
And hydrogen breaks all the rules.
The way it reacts
depends on the chemical situation.
It can form positive ions,
negative ions,
neutral atoms,
or neutral molecules.
Julien: So the simple rules that we used are correct.
Laureen: But they only take us so far.
Sarah: That's true.
The rules of chemical bonding are useful,
but they're never really absolute.
They are the best explanations we have
for what we observe.
Female narrator: The wheels are really light.
They want to make the wheels not only light,
but they want to make them strong as well.
So you won't see any steel wheels.
Steel is very heavy,
Most of the time they'll go to an alloy wheel
which is what this wheel is right here.
It's not only lighter, but it's much stronger and it can be trued.
So we can straighten the wheel,
make it round again,
whereas steel--you just have to throw it away.
It just cannot be straightened anymore.
But they're also making carbon fiber wheels--
using them for race wheels, so they're very, very lightweight.
You wouldn't use this everyday
because it will go through a lot,
but you can use them for a race wheel because they're light and very strong as well.
Male: Are they expensive?
Female: They are.. this wheel right here is worth about $700.
[rustling sounds]
♪
♪ Yo,
♪ let's wrap.
♪ Yo,
♪ let's wrap.
Nature often creates puzzles for us to figure out.
[clicking sound]
Bohr's model of the atom and the modern periodic table
help us explain a lot about the structure and behavior of the elements.
But our theoretical models are based on observation
and often we must adjust our theories
to fit the facts.
It's simply science.
[♪ music]
♪