In This Lesson:
Unit 3
Basic Chemistry
(Lesson 1 of 5)
Today is Tuesday,
October 13th, 2015
Stuff You Need:
Small bit o’
paper towel for
you/your
partner.
Pre-Class:
Suppose I had an atom the size of a professional football
stadium.
How big would the nucleus at the center of that stadium be?
Also: How important is an atom to a living thing?
Today’s Agenda
• Atoms and basic chemistry.
• Properties of water.
• Basically, a review of a lot of stuff you’ve
learned already. Again.
– Plus some stuff you didn’t. Again.
• Where is this in my book?
– Chapters 2 through most of 4.
By the end of this lesson…
• You should be able to describe the major
features of atoms, particularly those within
the first eighteen of the periodic table.
• You should be able to differentiate between
bonds formed among atoms.
• You should be able to identify life-supporting
properties of the water molecule.
Wait just a minute.
• Challenge Questions!
– Grab the whiteboards!
– Exclamation points!
– !!
Science in the Summer
• I teach a summer science course and the oldest
cohort of kiddies that attend are those entering
6th grade.
– The youngest? Entering 3rd.
• Occasionally we’re tasked with teaching them
rather high-level stuff and that can get
challenging.
• I once had to teach them youngins what an
element was. Specifically.
– Here’s how I did it.
Imagine a pizza…
• For those with poor imaginations:
http://www.louimbriano.com/wp-content/uploads/2011/07/cheese-pizza.jpg
Element Pz?
• Imagine your pizza being cut in two.
– Two halves of pizza, and each still has the cheese,
sauce, and crust necessary to call it a pizza.
• Now imagine it being sliced in half, and in half,
and in half, and in half, and in half, and in half,
and in half, and in half, and in half, and in half,
and in half, and in half, and in half, and in half,
and in half, and in half, and in half, and in half,
and in half again.
Elements
• Soon, you’ll have such a small part of that pizza
remaining that you really can’t call it pizza anymore.
• In the same way, an atom is the smallest part of an
element that retains the properties of that element.
– You can split an atom, but it’s not going to behave the
same anymore.
• An element, therefore, is one of 90 naturallyoccurring pure substances that make up ever’thing
and can’t be broken down into component
“ingredients.”
How small are we talking?
• Scale of the Universe!
– Scale of the Universe
Now then…
• I realize that’s not the first time you’ve heard that term
and definition, and that’ll be the same for most of
what we cover.
• As such, this is going to be a fast-moving review of a lot
of already-known information.
• I will also be making the assumption that you know a
fair amount of other information, which I will simply
leave out here.
– It’s nothing your biology teacher would have failed to
teach you.
• You are encouraged to seek more information (from
me or elsewhere) if you find your memory of these
concepts to be a little fuzzy.
Elements
• All elements can be differentiated by the
number of protons in their nuclei.
• No two elements have the same number of
protons as one another.
– A little like competitive exclusion, eh?
• The number of protons in an atom’s nucleus is
equal to the atomic number.
Isotopes and Mass
• Protons are not alone in the nucleus. There are also
neutrons.
– Neutrons and protons both weigh approximately 1 amu
(atomic mass unit).
• Therefore, the number of protons + the number of
neutrons in an atom = the mass number of an atom.
• Atoms of the same element cannot have different
numbers of protons, but they can differ in neutrons.
• Two atoms of the same element with different
numbers of neutrons are different isotopes.
• The weighted average (based on abundance) of all
atoms’ isotopes is their atomic mass.
Elements of Life
• Of those 90 elements, only about 25 occur in living
things in any meaningful amount:
– Carbon (C)
– Hydrogen (H)
– Nitrogen (N)
– Oxygen (O)
– Phosphorus (P)
– Sulfur (S)
– Potassium (K)
– Calcium (Ca)
~96% of living matter
~4% of living matter
• Remember them by “Chnops, KCaw!” (like a crow?).
Elements of Life
• Elements of Life – NOVA
Aside: Strontium (Sr)
• Between 1959 and 1970, scientists in St. Louis launched the
Baby Tooth Survey in which children’s primary (baby) teeth
were chemically analyzed.
– Over 300,000 by the end of the survey were tested.
• The findings?
– Children born between 1945 and 1965 had 100 times more
radioactive Sr-90 in their teeth than those born before.
– Sr-90 levels in teeth went up and down in conjunction with
nuclear bomb tests (due to spread of radiation through the
atmosphere).
• Ultimate results:
– President Kennedy and the Soviet Union reached a treaty to end
above-ground testing in 1963.
http://beckerexhibits.wustl.edu/dental/articles/babytooth.html
Bonding
• Before we talk about the finer points of bonding,
let’s start with a sort of pseudo-bond.
• To demonstrate this, everyone get out of your seats
and go talk to someone with whom you’d normally
speak if class hadn’t started yet.
• FREEZE!
• Look around the room. We’re not balanced.
• If we count the center of the room as the nucleus,
we clearly have clumps of electrons in certain areas
and not others.
• What does this mean?
Bond…Pseudo Bond
• Well, imagine we have another classroom (read:
atom) just outside our door in the hall.
• If a bunch of you are in a group near the wall, you
have brought a negative charge to that part of the
atom.
• The other atom’s electrons will get repelled by you,
causing them to move to the other side of the atom.
• You, then (being electrons), become attracted to that
other class’s nucleus, sticking our two classes
together.
• The process may even cause a third class to stick as
well.
Van der Waals Interaction
• These are known as van der Waals
interactions and lead to a weak,
temporary “bond.”
• This happens in every atom.
• It also explains how bugs can walk
on ceilings and geckos cling to
smooth glass:
Bonding
• Importantly, only rarely do those most common
elements ever exist in a pure form within the body.
– Typically, they’re stuck to another group of atoms, making
up a compound.
• We’ve talked about protons and neutrons, and while
they give an atom its identity, they don’t give an
atom its “bonding personality.”
– Electrons are the only subatomic particles involved in
bonding.
Electrons and Bonding
• Electrons are organized in various energy
levels moving away from the nucleus.
• The furthest-out electrons around an atom are
the valence electrons and figure in bonding.
• Atoms in the same column in a periodic table
(called a group or family) have the same
number of valence electrons and therefore
the same properties.
Electrons and Bonding
1 ve-
2 ve-
3 ve-
4 ve-
5 ve-
6 ve-
7 ve-
8 ve-
Types of Bonds
• If two elements share/fight-over their valence
electrons, they are engaged in a covalent bond.
– Awkward covalent bond demo! Volunteer?
• If two elements exchange valence electrons, they
are engaged in an ionic bond.
• Either way, the atoms are looking to obtain a full
valence shell, which has a capacity of 8 (or 2 for
Hydrogen).
• Let’s explore these two types of bonds by looking
at…the ocean.
First, the salt…
• The most common salt in the ocean is, well, sea
salt.
– Sodium chloride, or NaCl.
• From the periodic table, since Na is in the first
group, it has 1 valence electron.
• Cl has 7 valence electrons.
• So chlorine is looking for a valence electron, while
sodium is looking to get rid of one.
– Match.com!
– They form an ionic bond through a chemical reaction.
• Once the ionic bond has formed, the atoms are
referred to as a formula unit.
NaCl: Ionic Bond
• The exchange of an electron causes the sodium atom to
become a 1+ ion.
– Na+
• Similarly, the chlorine atom becomes a 1- ion.
– Cl-
• The positively and negatively charged ions then attract,
forming an ionic bond.
Chemical Reaction Video
• Chemical Reactions – NOVA
Covalent Bonding
• Of course, the salt is simply dissolved in the
ocean water.
– That makes the salt a solute – something that is
dissolved.
– The water, therefore, is the solvent – something
into which another substance is dissolved.
• While the salt is bonded ionically, the water
molecule is held together with covalent
bonds.
H2O: Covalent Bonds
• Oxygen has how many
valence electrons?
– 6.
• So it’d really like to gain two
more.
• The two hydrogen atoms each
need one valence electron.
• They can’t give them up
ionically or there’d be nothing
holding them together.
– Instead, they share valence
electrons. Co-valent.
Another Covalent Bonding Example
• Methane – CH4 – 1 Carbon, 4 Hydrogen
• Note that though only one bond is formed between
each hydrogen and the carbon, two electrons are
shared. A molecule is formed.
• When only one pair is shared, it’s a single covalent
bond.
Double and Triple Bonds
• When more than one pair of electrons is
shared, you have more than a single bond.
• Double bonds share two pairs of electrons.
• Triple bonds share three pairs of electrons.
The Catch: Polarity
• Another property emerges from covalent bonding
that is not present in ionic bonds.
• When electrons are shared between atoms,
they’re not necessarily shared evenly.
• If they are shared evenly, the bond is non-polar.
– There is no imbalance in negative charge density.
• If the atoms can’t play nice, however, the bond is
polar.
– One end of the resulting molecule has a slight negative
charge, the other is slightly positive.
This is a polar
molecule, because
the pulls do not
cancel each other.
This is a non-polar
molecule, because
the pulls do cancel
each other.
A figurative look at it?
• Think of when a child pulls on his/her parent’s
arm to lead him/her somewhere:
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Kid
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Other Kid
Polar and Non-Polar
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0m/section_12/679fdbbd60e31f9fd4067f5f482a8f2c.jpg
Dogs Teaching Chemistry
• Dogs Teaching Chemistry – Chemical Bonds
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Polarity and Hydrogen Bonds
• Did you notice how the other water molecules stuck
to the original one through a hydrogen bond?
• Concept first, then definition:
– Remember that kid that never shared toys, even when
s/he was supposed to? We’ll call him/her Selfish Sam.
– Let’s suppose you’re supposed to share a toy (electron)
with Selfish Sam.
– However, Selfish Sam is keeping it all to him/herself.
– Bored, you decide you’re going to go share a toy with
someone else, even though Sam is still your “partner”
(bonded atom).
Hydrogen Bonds
• A hydrogen bond occurs when one molecule
has an H bonded to an O, N, or F, and another
molecule has an O, N, or F.
• Oxygen, nitrogen, and especially fluorine are
all very selfish atoms, so when H is supposed
to share with them, it gets shortchanged.
– Consequently, a neighboring molecule attracts it.
• By the way, the “selfishness” of an atom is its
electronegativity.
Hydrogen Bonds
• Hydrogen bonds are
considered an
intermolecular force.
• Key: Hydrogen bonds occur
BETWEEN molecules and
therefore are different from
covalent and ionic bonds.
• Key: Hydrogen bonds are a
result of polarity.
• Key: Water is polar.
Water: The Elixir of Life
• Let’s use this opportunity to transition into
water’s properties.
• Water is unique as a molecule because of a
specific set of properties.
• Other molecules have some of these, but
none have all and are as plentiful as water is.
• Let’s look at a summary slide and then explore
them individually.
Properties of Water: Summary
• It has a high specific heat, so it takes a LOT of
energy to get it to go up or down in temperature.
• Water cools surfaces from which it evaporates.
• Water is pH neutral.
• It’s polar so:
– Its density is lower as a solid than a liquid.
– It can stick to itself.
– It can stick to other stuff.
– It can dissolve other polar stuff.
Specific Heat
• Specific heat is the amount
of energy it takes to raise the
temperature of one gram of
a substance by one degree
Celsius.
• Water has a particularly high
specific heat, so it does not
easily change temperature.
• At the beach, if the air
temperature is 80°, how
warm is the water?
Specific Heat – Big Picture
• Because water doesn’t swing much in
temperature…
– This is called thermal inertia, by the way.
• …it serves as a regulator for the environment.
• It explains why, if you’ve ever been to the
desert, you need a jacket at night, yet during
the day, it feels like the sun has gotten closer
to the Earth.
http://marool.com/wp-content/uploads/breaking-bad-heisenberg-marool1.jpg
Thermal Inertia
• For example, New Mexico (left) and Hilton Head Island,
SC (right) are the same latitude, yet they have different
climates.
• Having water around prevents the temperature from
swinging dramatically over any given time period.
Evaporative Cooling
• When water evaporates from a surface, it
cools that surface.
– This is known as evaporative cooling and is
caused by water absorbing energy as it turns
into a gas.
– That’s why it’s cold when you get out of the
shower, why you sweat in the heat, and why
animals pant.
• And why vultures “pee” on their legs.
Water is pH Neutral
• The Arrhenius definition of acids and bases says
that acids produce H+ (hydrogen) ions in solution
and bases produce OH- (hydroxide) ions in
solution.
– Key: H+ ions are really just protons.
• When water dissociates (splits apart), it makes
one H+ ion (acid-making), and one OH- ion (basemaking).
– So the acid and base parts of H2O balance one
another, keeping water at a neutral pH of 7.
• At 25° Celsius.
Water is pH Neutral
• Heads-up: Sometimes that H+ ion (proton) joins
with another water molecule and makes
hydronium (H3O+).
– Hydronium is just as acid-causing as H+, in a way.
• So if H+ (or H3O+) causes acidity and OH- causes
basicity, then…
– …if [H+] > [OH-], or [H3O+] > [OH-], it’s acidic.
– …if [OH-] > [H+], or [OH-] > [H3O+], it’s basic.
– …if [H+] = [OH-], or [H3O+] = [OH-], it’s neutral.
• [X] means “concentration of X.”
Acids, Bases, and You
• One quick note:
• Your blood must maintain a pH between 7.35 and
7.45, but lots of edible things have pH values
outside that range.
– So how does a juice box not kill you?
• Your body uses buffers, which are substances
that minimize the impact of an acid or a base on
pH level.
• Human blood buffers are bicarbonate and
carbonic acid. They work in tandem.
Common Acids and Bases
Good to know…
• Acids:
– Gastric fluids (hydrochloric acid – HCl)
– Urine (uric acid/urea)
– Fruits (especially citrus)
• Bases:
– Excretory Waste (ammonia – NH3)
– Intestinal fluids
Polarity Product: Density
• As water freezes,
hydrogen bonding
forces it into a
hexagonal shape,
forcing it to expand and
lower its density.
• It’s why soda cans
explode in the freezer
and also keeps lakes
from freezing solid in
winter.
– It’s also why snowflakes
tend to have six sides.
http://cnx.org/resources/2a957225714f4163c049c26fd704a3cd/Figure_44_02_05.png
Polarity Product: Cohesion
• Because of water’s polarity,
water molecules can stick to
one another – cohesion.
• Cohesion allows water to
overfill a glass and, in part, to
suspend itself from a leaky
faucet for a little while before
dripping.
• Cohesion at water’s surface is
called surface tension.
– It’s why belly-flops hurt.
http://3.bp.blogspot.com/-N2-NE8Wm4c8/UEzMbtVULYI/AAAAAAAAABc/6VnqBGu3plo/s1600/pennie+with+water.jpg
http://www.aapt.org/programs/contests/winnersfull.cfm?id=2329&theyear=2011
Cohesion in Space
• If we eliminate gravity from the picture, we
can really see how water behaves, particularly
with regard to cohesion and adhesion.
• In space, with no meaningful gravity, water is
almost entirely bound by intermolecular
forces.
• Let’s take a look…
Polarity Product: Adhesion
• Water’s polarity also
allows it to stick to other
objects.
– Yes, water is very sticky.
• This is the other reason
why a droplet of water
sticks to the underside of
a faucet before it
eventually falls.
Adhesion + Cohesion = Capillary Action
• By themselves, adhesion and cohesion are not incredibly
important.
• Put them together, however, and they make up capillary
action – motion of water in a small tube.
• It explains why water climbs up a straw in a glass.
• It also explains why blood can flow through a small tube
without any pressure, and why transpiration in plants works.
– Ever wonder how water gets to the top of a tall tree?
Capillary Action Video
• Hackman Video Clips
Water Can Dissolve Other Polar Stuff
• Okay, this is the big one for this
unit.
• Remember that, being polar,
water has positive and negative
“ends” to the molecule.
• Water can then stick to other
polar molecules.
– It surrounds them and invades
their space.
– We call this “shell” of water
a…hydration shell.
• It’s like this:
Quick Note: Solutions
• Not everything that’s mixed together is a solution.
It needs to do the hydration shell thing.
– Suspensions are mixtures where one substance will fall
out of solution if not stirred or agitated.
• Like mud in water. The mud settles out after time.
• Blood is a suspension (with respect to red blood cells).
– Colloids are mixtures that don’t settle, but also don’t
have hydration shells.
• Paint is a colloid.
Hydrophilic vs. Hydrophobic
• Key: Polar substances can dissolve in water, thus they
are hydrophilic (water-liking).
• Key: Non-polar substances cannot dissolve in water,
thus they are hydrophobic (water-hating).
http://www.ecofriendlymag.com/wp-content/plugins/wp-o-matic/cache/9e8b0_bp-leak-gusher.jpg
Get it?
Hydrophobic/Hydrophilic
http://static.guim.co.uk/sys-images/Environment/Pix/columnists/2010/5/20/1274366784453/Deepwater-Horizon-oil-spi-006.jpg
Hydrophobic/Hydrophilic
http://www.newsoxy.com/images/0706/tar-balls-3.jpg
Hydrophilic/Hydrophobic
http://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/oil_06_03/o01_23681845.jpg
http://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/oil_06_03/o02_23681001.jpg
http://www.yoganonymous.com/wp-content/uploads/2010/06/save-the-sea-turtles.jpg
Hydrophilic/Hydrophobic
• The behaviors of hydrophilic and hydrophobic
molecules are, quite literally, life-giving.
• We’ll start looking in greater depth with our
next lesson, but for now, remember this:
– Polar = Hydrophilic = Likes Water
– Non-Polar = Hydrophobic = Hates Water
Closure
• TED: Christina Kleinberg – How Polarity Makes
Water Behave Strangely
• Bill Bryson – Atoms