(Lesson 1 of 5) Today is Tuesday, October 17 , 2017 · Science in the Summer ... Baby Tooth Survey in which children’s primary (baby) ... •Oxygen, nitrogen, and especially fluorine

Today is Tuesday,October 17th, 2017

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?

In This Lesson:Unit 3: Cells

Basic Chemistry(Lesson 1 of 5)

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 naturally-occurring pure substances that make up ever’thingand 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)• Remember them by “Chnops, KCaw!” (like a crow?)

~96% of living matter

~4% of living matter

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.

A figurative look at it?

• Think of when a child pulls on his/her parent’s arm to lead him/her somewhere:

ParentKid

This is a polar bond,

because “Parent” is

likely stronger than

“Kid.”

Other Kid

This is a polar molecule, because

the pulls do not cancel each other.

Add another kid with

equal strength and

you have another polar

bond.

This is a non-polar molecule, because the pulls do cancel

each other.

But if “Other Kid” is

ripped, the pulls may not

cancel out.

This is a polar molecule, because

the pulls do not cancel each other.

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

But…since oxygen is such a strong atom, it doesn’t share electrons nicely.Having all that negative charge built up around oxygen causes that end of the molecule to take on a negative charge…

…and all that’s left on the other end are the hydrogen protons, causing that end of the molecule to take on a positive charge…

…which causes neighboring water molecules to form hydrogen bonds with the first one.This is the source of cohesion/surface tension, and why it hurts to do a belly-flop.

In a diagram…

HH

O-

Meet water: (say hi)There are 8 total valence electrons in the molecule.

- - ---

--

-

++-

++ -+ +

Hydrogen Bond

Covalent Bond

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 anothermolecule 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.

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.

http://marool.com/wp-content/uploads/breaking-bad-heisenberg-marool1.jpg

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 (base-making).– 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 BasesGood 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://www.aapt.org/programs/contests/winnersfull.cfm?id=2329&theyear=2011

http://3.bp.blogspot.com/-N2-NE8Wm4c8/UEzMbtVULYI/AAAAAAAAABc/6VnqBGu3plo/s1600/pennie+with+water.jpg

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 incrediblyimportant.

• 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://www.yoganonymous.com/wp-content/uploads/2010/06/save-the-sea-turtles.jpghttp://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/oil_06_03/o02_23681001.jpghttp://inapcache.boston.com/universal/site_graphics/blogs/bigpicture/oil_06_03/o01_23681845.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