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Chapter 4CH1a,1h,2a,2b,2c,2i

Atomic Structure

Chemical History covered Ch 4, sections 1&2 and Ch 5,

section 1http://imagecache5.art.com/p/LRG/6/667/USYC000Z/fedex-field--washington-d-c-.jpg

Has anyone been to a professional football stadium or a major college football stadium?

If the nucleus of an atom was the size of a marble, sitting at the 50 yard line, the electrons would be about the size of really little gnats (bugs) whizzing around the top rows of the upper deck.

So then, most of the atom is just “empty space.”

Just how small is an atom?http://kara.allthingsd.com/files/2009/04/penny.jpeg

Let’s use a penny as an example (picture, in slide show, is approximately life-size). A penny, if made of pure Cu (copper) would have 2.4 x 1022 atoms. That’s 24,000,000,000,000,000,000,000 atoms, btw.

If you lined up 100,000,000 atoms, they would make up a line of approximately 1 cm. So, 2.4 x 1022 atoms, if lined up would make a line that was approximately 2.4 x 109 KILOMETERS long.

Approx. 1 cm from arrow to arrow (in slide show mode)

Some of you are driving me crazy…you can’t see atoms, BUT they do exist. You believe in zombies, don’t you?

What does an atom look like?http://www.lanl.gov/orgs/pa/newsbulletin/images/Isotopes_logo.jpg

In your notes, draw a simple picture of an atom. How about Lithium.

What did you draw?

AAA baseball club Albuquerque Isotopes logo (you need to know what isotopes are!)

Atomshttp://upload.wikimedia.org/wikipedia/commons/thumb/e/e1/Stylised_Lithium_Atom.svg/270px-

Stylised_Lithium_Atom.svg.pnghttp://www.solarsystempictures.net/

Most people probably drew a nucleus of some type with electrons orbiting around it.

Possibly it looks a little like a mini solar system.

Atoms are composed of Protons (in the nucleus).

Mass of 1 amu; charge = +1 Neutrons (in the nucleus).

Mass of 1 amu; charge = 0 Electrons (moving around the

nucleus). Mass of 0 amu; charge = -1

NeutronProtonElectron

Lithium

Sun=Nucleus

Planets=Electrons

Subatomic Particles: Hint, you need to know this!

Particle ACTUAL charge

Relative mass & charge(1 amu = mass of a proton)

Actual Mass of Particle

Proton+1.6 x 10-19

coulombs 1 amu / +1 1.67 x 10-24g

Neutron0 1 amu / 0 1.67 x 10-24g

Electron-1.6 x 10-19

coulombs 0 amu / -1 9.11 x 10-28g

Electrons

Atoms can gain or lose electrons.

Atoms can NEVER gain or lose protons!

If an atom loses an electron, it becomes a positive ION. Atoms can lose 1, 2 or 3 electrons

If an atom gains an electron, it becomes a negative ion. Atoms can gain 1, 2, or 3 electrons

Protonshttp://www.periodictable.com/Items/020.6/index.html

Protons determine the “identity” of an atom.

The number of protons is a property called “atomic number.”

Atomic numbers are on the periodic table. C has 6 protons Ca has 20 protons

Atomic Number

# Protons = # ElectronsIf it is not an ion!

Atoms are NEUTRAL (have the same number of protons and electrons).

If the charges don’t balance each other out, then you have an ion.

Protons MUST equal electrons if the atom has no charge.

Neutronshttp://www.ct.infn.it/~rivel/Archivio/chadwick.jpg

http://kwisp.files.wordpress.com/2009/05/adventures-jimmy-neutron-300-032707.jpg

Neutrons are also located in the nucleus of the atom.

The neutron was the last particle discovered, by James Chadwick, a former student of Rutherford (who discovered what?).

He used paraffin wax to discover neutrons. This was done in 1932.

Atoms can have different numbers of neutrons. These are called ISOTOPES.

Ooops, wrong neutron!

Chadwick

The Nucleushttp://www.chemicalelements.com/bohr/b0019.gif

Since the neutrons are located in the nucleus, with the protons, substantially ALL of the mass of the atom is contained within the nucleus.

Mass of nucleus in diagram 0.0000000000000000000000651 g

Mass of electrons 0.0000000000000000000000000173 g

In other words, if electrons (all 19 of them) weighed as much as a piece of notebook paper, the nucleus’ weight would be equal to 3,763 pieces of paper.

What element is this??

Strong Nuclear ForceUp,Down,Top,Bottom,Strange,Char

mhttp://www.antonine-education.co.uk/Physics_AS/Module_1/Topic_5/strong_force.jpg

Positively charged things repel other positively charged things, right? Why do all the protons stick together in the nucleus?

Why doesn’t it just spontaneously break apart? The answer is strong nuclear force.

It’s the strongest force in the universe. It is far, far stronger than gravity. It only can be

felt when the particles are extremely close together, like when they are packed together in the nucleus.

Protons and neutrons are made of quarks. It is thought that the quarks in neutrons are

different from the quarks in potons, so we think that the neutrons actually help to hold the nucleus together.

The secret’s in the attractions between the quarks…Proton = uudNeutron = ddu

Models of the Atomhttp://www.fiu.edu/~zhangj/cartoon_quantum3.gif

Scientists, starting with Dalton, came up with models of the atom, to help understand it and help to predict its behavior. Solid Sphere Model Plum Pudding Model Nuclear Model Planetary Model Quantum Mechanics

Do you remember who did each one?

ATOMIC NUMBER

The “atomic number” is the number of protons.

We sometimes use a Z to represent atomic number.

Z does NOT equal the number of electrons. Sometimes it does, but that

is coincidence. But Z is always the number

of protons.

So, if “ProtonMan” was a superhero, he’d have a “Z” on his suit??

Do Not Assume the Atom has a CHARGE!

Unless you are TOLD that the atom has a charge, you should assume it has no charge, and therefore, # of protons = # of electrons.

The number of protons cannot change. EVER! If the number of protons changes, it’s no longer the

same element.

Atoms can gain or lose electrons, but they can NOT gain or lose protons in any chemical reaction. This is part of Daltons’s Atomic Theory.

Schwartz’s Law(a law I made up…hey, it’s my class)

To calculate the number of electrons, use this little formula.

# of Electrons = Z – IC Where Z = atomic number and IC = ionic charge

Ex: Suppose we have a sodium ion with a + 1 charge. How many electrons does it have? Atomic number (Z) is 11 (find this on Periodic Table) and ionic

charge is 1. # electrons = 11 - 1 = 10

Ex: Suppose we have a sulfur ion with a - 2 charge. How many electrons does it have? Atomic number (Z) is 16 and

ionic charge is -2. # electrons = 16 - (-2) = 16 + 2 = 18

Finding Neutronshttp://www.atomicarchive.com/Physics/Images/isotopes.jpg

How do we calculate how many neutrons we have?

In order to do that, we need to look at another property, called mass number.

The mass number of an isotope = THE SUM of protons and neutrons.

We will use another formula # Neutrons = A – Z A = Mass Number So, what is Z again?

Hey these are isotopes again. Isotope = same # of protons but a different # of neutrons.

6 neutrons

8 neutrons

Finding Neutronshttp://www.lbl.gov/abc/Basic.html#Nuclearstructure

Let’s look at an example.

An atom of Bromine (Br-80) has Z = 35 and Mass Number = 80. How many neutrons does it have? (Br-80 doesn’t mean bromine with a charge of -80. When they write it like that, it’s a DASH and 80 is the mass number)

# Neutrons = Mass Number - Atomic Number # Neutrons = 80 - 35 = 45

Hydrogen’s Isotopes

An atom of Deuterium has Z = 1, and Mass Number = 2. How many neutrons does it have? Since Z = 1, deuterium must be some

type of hydrogen. We use the symbol D to represent H-2. We also use the symbol T to represent H-

3.

Deuterium is a form of hydrogen. When deuterium reacts with oxygen it forms something called “heavy water.” Heavy water is represented with the

formula D2O. It is still water, but it has different PHYSICAL properties

# of Neutrons = Mass Number - Z = 2 - 1 = 1

Isotopes of hydrogen:

1H = hydrogen

1 proton, 0 neutron

2H = deuterium

1 proton, 1 neutron

3H = tritium

1 proton, 2 neutrons

Hydrogen is the only element with special names for isotopes.

Special note

Heavy Waterhttp://www.damninteresting.net/content/heavy_water_ice.jpg

Here’s an interesting fact…

Ice cubes made out of “heavy water” will not float. They sink to the bottom. So it has different physical properties.

Although it PROBABLY tastes the same, you should NOT drink it though. Too much of it can really mess up your system (and probably kill you).

Isotopes of Goldhttp://www.usagold.com/images/gold-coins-images.jpeg

http://finestimaginary.com/shop/images/medium/jewellery/au_MED.jpg

Look at gold (Au) on the periodic table. It says that the mass = 196.967. Since mass number and atomic

number are ALWAYS whole numbers, how do we get .967?

The answer is that the atomic masses on the periodic table are averages.

Isotopes differ from each other in the number of neutrons. They behave the same CHEMICALLY because all isotopes of the same element have the same number of protons.

Carats of Goldhttp://www.usagold.com/images/gold-coins-images.jpeg

http://finestimaginary.com/shop/images/medium/jewellery/au_MED.jpg

10K and 14K gold are not different isotopes of gold.

They are different ALLOYS. 10K and 14K are

homogeneous mixtures of copper and gold.

K = 24 x (Massgold / Massalloy) 10K = 41.67% gold 14K = 58.33% gold 24K = 100% gold Current price = $42.60/g

Average Atomic Mass

How do we calculate the average atomic mass?

To do so, you need to know 2 things: All possible isotopes for an element The percent abundance for each (in other

words, how much of the whole is represented by each isotope).

Math Alert

Average Atomic Mass

Let’s look at an example: Chlorine has 2 isotopes

35Cl which is 75.77% of the total amount of chlorine.

37Cl which is 24.23% of the total amount of chlorine.

What is the average atomic mass of Chlorine?

Math Alert

Proper Rounding of Atomic Masses on Periodic Table

In our class, we are always going to round average atomic masses to 1 decimal place.

So, we’ll round 35.49 to 35.5 and that’s the average atomic mass of Chlorine that we’ll use.

Why can’t you just average 35 and 37 (the two isotopes) and get 36 as the average atomic mass? Why is that wrong?

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The End

Next you should look at the Chapter 5 power point.