Daniel R. Barnes Init: sometime about a year before 10/4/2006.

Daniel R. BarnesInit: sometime about a year before 10/4/2006

. . . describe what atoms are made of, in terms of size, mass, electric charge, location, and motion.

“SWBAT = “Students will be able to”

. . . explain how theories and laws evolve over time.


When you click the link above and play with the slider on the scale of the universe thingie, make sure to go all the way down to the size of molecules, atoms, the nucleus, and individual protons, neutrons and electrons. You really need to see just how small that stuff is.

http://scaleofuniverse.com/

Thank you, Francisco Lerma and Aranza Guzman for helping me fix the link! DRB 9/8/2014

http://scaleofuniverse.com/

What does “subatomic” mean?

A submarine goes underwater.

109876543210-1-2-3-4-5-6-7-8-9

-10

“Sub-” means “below” or “under”.

When you start giving number values to altitude, whether you’re talking about airplane altitude or the number of the floor in a building, “under” starts to mean . . . “less than”.

On the vertical number line to the right, “2” is below “3” because 2 is less than 3.

A subatomic particle is a speck of matter that is less than an atom.

109876543210-1-2-3-4-5-6-7-8-9

-10

109876543210-1-2-3-4-5-6-7-8-9

-10

“Sub-” means “below” or “under”.


If the number line to the right were a thermometer, temperatures below zero would be called . . . . . . “sub-zero” temperatures.

“Sub-zero” is below zero.

“Sub-zero” is less than zero.


A “subatomic particle” is less than an atom.

There are three subatomic particles you have to get to know . . .

A “subatomic particle” is just a part of an atom.

mass = 1.007 amu

mass = 1.009 amu

mass = 0.000549 amu

charge = + 1

charge = 0 = “neutral”

charge = -1

repulsion

repulsion

attraction

You’re rePULsive!

You’rerepulsive!

no reaction

no reaction

no reaction

* Bringing a charged object near a neutral object can cause the neutral object to develop + & - zones, which can make the neutral object attracted to - & + objects, so my jury is not yet out on neutrons . . .

mass = 1.007 amu

mass = 1.009 amu

mass = 0.000549 amu

charge = + 1

charge = 0 = “neutral”

charge = -1

Which two particles are the heaviest?

mass = 1.007 amu

mass = 1.009 amu

mass = 0.000549 amu

Who discovered the electron?

He didn’t do all the work, though.

Joseph John Thomson, 1897

Crookes tube

William Crookes1832-1919

NOTE: A normal dry cell (“battery”) only provides 1.5 volts. This experiment required thousands of volts.

magnet

Electron momentum or radiometric effect?

This is more or less a picture of Thomson’s “plum pudding” model of the atom.

It’s an improvement over Democritus’ and Dalton’s models in that it states that an atom CAN be broken into pieces.

Who discovered the nucleus?

ErnestRutherford,1911

1909

HansGeiger

ErnestMarsden

omfg!

ZnS

Imagine a marble on the 50-yard line.

That’s how small the nucleus of an atom is compared to the atom as a whole.

This cartoon drawing of an atom is largely based on the “solar system” model of the atom that Rutherford came up with after the gold foil experiment.

It’s full of flaws, but it was an improvement on Thomson’s “plum pudding” model.

Note that the nucleus in this cartoon is shown as being far too . . .

BIG.

(Remember the marble on the 50 yard line!)

Got graph paper?

Materials reminder:

You’ll need it next week

real rabbit

cartoon rabbit

real atoms

cartoon atom

(same picture as page 103 in section 4.1 of your book)

Cartoon electron orbit More realistic electron orbit

So, what’s wrong with the way I drew this atom?

The nucleus is far too large. Let’s shrink it.

Is that small enough?

Okay. Let’s shrink it again, then.

Is that small enough for you?

Okay. Is THAT small enough?

Let’s shrink it again, then.

Why not?

Yep. If you can see it, I drew it too big.

An atom may be tiny, but it’s gigantic compared to the nucleus in its center.

That’s pretty strange, considering that the nucleus is where over 99% of the atom’s mass is.

Atoms are made mostly of . . .

And you’re made of atoms, so . . .

. . . YOU’RE made mostly of empty space.

Hey, Mr. Barnes! I

got a question!

If I’m made mostly of

empty space,

And you’re made mostly

of empty space . . .

How come it hurts so bad when I kick you in the

nuts?

Since we’re made mostly of empty space, you’d think we’d just pass through each other like ghosts.

Instead, we bounce off of each other like billiard balls.

Why is that?

Ask me again when we’ve

done the static electricity lab.

Okay. Can we go to the “Did you get it” questions, then?

We HAVE done the static electricity lab!

Explain! Explain!

Do you remember what happened when we charged up both balloons and tried to bring them close together?

Think about that for a bit while we imagine me kicking a wall.

An atom in my foot An atom in the wall

As my foot gets closer and closer to the wall, what parts of the atoms come into contact first?

The electrons are on the outside of the atom, so they’re the parts that come closest together. The electrons are the ambassdors of an atom.

Let’s forget about the atoms and just focus on the electrons.

Well, okay, they repel each other. Electrons don’t really have feelings.

An electron in my foot An electron in the wall

How do electrons feel about each other?

They’re both negatively-charged, so . . .

They hate each other.

Yes we do, and you just hurt mine!

I don’t care if you’re sorry.

You’re gonna hear from my

lawyer!

So, anyway, electrons push each other away. They feel an “electrostatic repulsion” for each other.

An electron in my foot

In order for my foot to get closer to the wall, I have to exert force to get my electrons to get closer to its electrons.

The force my muscles exert has to be at least as strong as the repulsion between our electrons.

An electron in the wall

kQ1Q2

R2Fe =


Electrostatic Force

Charge on the first objectCharge on the other object

Distance between the two objects

There’s an equation that predicts the electrical force between two charged objects. It looks a lot like Newton’s law of universal gravitiation.


kQ1Q2

R2Fe =


According to the equation, if the charge of either particle gets larger, the force gets larger also.

When the numbers on the top of a fraction get larger, the value of the fraction gets larger.

( )


kQ1Q2

R2Fe =


According to the equation, if the distance between the objects gets larger, the force gets weaker.

When a number on the bottom of a fraction gets bigger, the value of the fraction gets smaller.

( )


kQ1Q2

R2Fo

rce

(Fe)

Distance (R)

Fe =


If you make a graph of force versus distance . . .

It’s a downward-swooping curve.


kQ1Q2

R2Fo

rce

(Fe)

Distance (R)

Fe =


The closer the two electrons get . . .

the stronger the repulsive force between them gets.


kQ1Q2

R2Fe =


Let’s imagine the electrons getting as close as possible, close enough to touch.What’s the distance between two touching objects?

If two objects are touching, there is no longer any distance between them.

In other words, if two objects are touching, R = 0.

If the number on the bottom of a fraction equals zero, what is the value of the fraction?

=


So, to get my atoms to get close enough to touch the wall’s atoms, I have to exert an infinite amount of force in order to overcome the electrostatic repulsion between my electrons and its electrons.

I’m just not that strong.

It may look like my foot touches the wall when I kick it, but actually, my foot never really does touch it.

My foot gets really close to the wall, but the outside surfaces of my atoms never quite touch the outside surfaces of the wall’s atoms before they bounce back.

Well, that was a fun little mental tangent, but let’s get back on track and see if we’ve lived up to our SWBAT’s for this lesson . . .

Q1: What are the three main subatomic particles that atoms are made of?A: protons neutrons, and electrons

Q2: Where are protons, neutrons, and electrons found?A: Protons and neutrons are found in the nucleus. Electrons orbit the nucleus, grouping into shells.

Q3: Compare the masses of protons, neutrons, and electrons.A: Protons and neutrons have a mass of about 1 amu each. Electrons weigh* much less (only 1/1836th of an amu each).

Q4: Compare the electric charges of our subatomic particles.

A: Protons are +1, neutrons are neutral (zero), and electrons are -1.

Q5: How do the various subatomic particles feel about each other?

A: Protons repel protons and electrons repel electrons. Protons and electrons attract each other. Neutrons don’t care about anyone else, and the feeling is mutual.

Q6: Describe the charge, mass, and volume of the nucleus, in comparisson to the atom as a whole.

A: Although over 99% of an atom’s mass is crammed into its nucleus, the nucleus is so small compared to the atom as a whole that it is like a marble compared to a football stadium. The nucleus is positive because of the protons in it.

TPS2: How did Rutherford’s discoveries build upon what his mentor, J. J. Thomson, had discovered?

Thomson discovered the electron, but he mistakenly believed that the positive charge in an atom was spread evenly throughout its volume. Rutherford showed that the positive charge was concentrated in a very small dot in the center.

TPS1: What did Rutherford discover about the anatomy of an atom, and how did he do it?

A: By shooting alpha particles at gold foil, Rutherford discovered that there is a very small, dense, positively-charged particle in the center of an atom. He called it the “nucleus”.

Don’t move on to the atom-drawing activity until you’ve tried Mr. Barnes’ atom rules determination activity.

http://www.hhscougars.org/ourpages/auto/2009/9/17/50465291/atom%20rules%20determination%20activity%20worksheet%20DRB.pdf

Click the green rectangle to get the worksheet

http://www.hhscougars.org/ourpages/auto/2009/4/24/38513449/atom%20rules%20determination%20activity%20DRB.ppt

Click the orange rectangle to browse the power point

. . . draw atoms correctly.


# = #

Li 3

Li6.94

3

7-34

neutral, so 3

= “Sigma”

Sigma is a symbol used in math & science. It means “sum” or “total”.

# neutrons = mass # - atomic #

mass # = # protons + # neutrons

# = #

Li 3

Li6.94

3

7-34

neutral, so 3

Which two particles are the heaviest?

Where is almost all the mass located?

Got graph paper?

Materials reminder:

User name = hwbrainpop

Password = cougar1

View the “Atoms” and “Atomic Model” cartoons once you’ve logged in.

NOTE: The student account can only be used during the hours of 8AM – 4PM.

# = #

H 1

H1.01

1

2-11

neutral, so 1

2

, so 4 – 2 =

Be 4

Be9.01

4

9-45

2 missing 2

2+

10, so 8 + 2 =

O 8

O16.00

8

16- 88

2 extra

2-

9, so 6 + 3 =

C 6

C12.01

6

13- 67

3 extra

3-13

It ain’t over til the lady with the shoe on her head says it’s over.

It’s over.

Here is the Los Angeles Memorial Coliseum as seen from a satellite.

Click here to go to the website from which this image was taken.

Daniel R. Barnes Init: sometime about a year before 10/4/2006.

Documents

Transcript of Daniel R. Barnes Init: sometime about a year before 10/4/2006.