Today is Thursday,February 19th, 2015

Pre-Class:Exactly how big is an atom, would

you say?

Of what is it made?

Take a laminated periodic table, too!

In This Lesson:Atomic Structure

(Lesson 6 of 6)

Stuff You Need:WorksheetLaminated Periodic Table

Today’s Agenda

• This is a two day lesson!• Day 1:

– Atoms– Subatomic Particles– Notation– Ions

• Day 2:– Isotopes– Calculating atomic mass– Isotope Bean Lab

• Where is this in my book?– P. 101 and following…

By the end of this lesson…

• You should be able to describe the three main components of an atom and what happens when each of these components changes in number.

• You should be able to calculate atomic mass using a weighted average.

How Small Are We Talking?

• http://learn.genetics.utah.edu/content/begin/cells/scale/

• Scale of the Universe.lnk

Aside: You’re a Star!

• Remember the Law of Conservation of Matter?• Here’s a weird thought…since atoms are never

destroyed or created (only “recycled”), the same atoms that were in stars at the beginning of time are partially in YOU right now!

• The same goes for our ancestors.– It’s estimated that around 1 billion of your many atoms

once belonged to Shakespeare. Some of the rest may have come from Henry VIII or Julius Caesar or anyone else that died quite a while ago.

• Also, one more thing – that means that most of the water you drink and in your body is recycled dinosaur urine. Yum!http://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/NGC_4414_(NASA-med).jpg/300px-NGC_4414_(NASA-med).jpg

Atoms and Subatomic Particles

• Atoms are the smallest particle of an element that still behaves like that element.

• Generally, atoms are arranged such that there is a dense center core (the nucleus) surrounded by a diffuse field.

• In (almost) every atom, there are the following three key subatomic particles:– Proton– Neutron– Electron

Aside: Sub-subatomic Particles

• Below the level of protons, neutrons, and electrons are other subatomic particles.

• Without going into too much depth:– Protons are made of three quarks, two “up”

and one “down.”– Neutrons are made of three quarks, two

“down” and one “up.”– Electrons are made of…electrons.

On your worksheets…

• Look to #8.

Subatomic Particles

• Protons– Location: Nucleus– Charge: Positive– Mass: 1 amu– Symbol: p+

– Discovered by: Eugen Goldstein

Subatomic Particles

• Neutrons– Location: Nucleus– Charge: None– Mass: 1 amu– Symbol: n0

– Discovered by: James Chadwick

Neutrons

http://24.media.tumblr.com/tumblr_m095muHVGa1rq6f8po1_500.jpg

Okay, one more…

• Why can’t you believe atoms?– Because they make up everything!

• Ishaan D. (September 2013)

Another, you ask?

• What did one atom say to the other atom?– Do these protons make my mass look big?

Subatomic Particles• Electrons

– Location: A cloud around the nucleus, moving at high speeds• Actually, VERY FAR from

the nucleus, too.– Charge: Negative– Mass: 0 amu (so small it’s

rounded to virtually nothing)

– Symbol: e-

– Discovered by: JJ Thomson

Aside: Empty Space

• Okay, so you notice how most of the atom is empty space?

• It turns out that nothing, really, is solid in our everyday lives. Your chairs, your desks, your notebooks, YOU - they’re all mostly empty space.

• In fact, when two objects come in contact with each other, they actually don’t.– What I’m saying is you’re not actually touching your chairs

right now.• Two objects that “collide” are actually just experiencing

electrons repelling one another.– Without this force, a bowling ball would go through the pins.

Anyway…

• Take a look at your periodic tables.• We’re going to do a little exercise with ‘em.

Dmitri Mendeleev

• The inventor of the modern Periodic Table:

http://reich-chemistry.wikispaces.com/file/view/Dmitri_Mendeleev.jpg/98117907/Dmitri_Mendeleev.jpg

Trimmed his beard and hair

once a year.For reals.

Atomic “Rules”

1. Is there a relationship between the number of protons and neutrons in an atom? What about protons and electrons?

2. Compare atomic number (that’s in the upper-right corner) to the number of protons in the element.

3. What about atomic mass? How might that be calculated?

How Many p+, n0, e-?• Protons (p+)

• Represented by the atomic number.• Neutrons (no)

• Mass number minus atomic number.• Electrons (e-)

• Same as the number of protons in neutral atoms.

• Mass number• Protons + Neutrons• Can be written as either Na-23 or

23Na.

Atomic Number

Mass Number

Atomic Notation

• With all these statistics, the formal notation of these atoms can be confusing. Here’s an example of the nuclear symbol:

http://www.hferrier.co.uk/standard/topic3/nuclide.gif

• How many protons, electrons and neutrons are in the following atoms?

• 9Be– Protons = 4 Electrons = 4 Neutrons = 5

• 20Ne– Protons = 10 Electrons = 10 Neutrons = 10

• 35Cl–Protons = 17 Electrons = 17 Neutrons = 18

How Many p+, no, e-?

17

10

4

On your worksheets…

• Take 6.57 minutes and try #1-3 and 5.– For #1, leave out:

• Atomic Mass• Isotope• Isotope Name

– For #5, leave out:• Isotope Name

• NOTE: “Atomic mass/weight” and “atomic number” are different. DO NOT use atomic mass or atomic weight for now.

For a little practice…

• …we’re going to build some atoms with our computers using one of two methods:– PhET – Build an Atom– ExploreLearning – Element Builder

PhET

• Visit this website (listed in my Chem Links page):– http://phet.colorado.edu/en/simulation/build-an-

atom• Once here, click “Run Now.”• When the applet loads, hit the + signs on the right

side next to “Symbol,” “Mass Number,” and “Net Charge.”

• Then, start building atoms by clicking and dragging subatomic particles to the appropriate places.

Element Builder

• [Log-in Instructions]

Build Your Own Elements

• Build the following elements (don’t forget all the subatomic particles):– Hydrogen, Oxygen, Lithium, Carbon

• Questions to ponder:– What happens when you change the number of protons?– What happens when you change the number of neutrons?– What happens with you change the number of electrons?

Changing Protons

• Changing the number of protons changes the element.

• In other words, the atomic number of an element never changes.– It is always equal to the atomic number.

Changing Neutrons

• Changing the number of neutrons in an atom changes the mass number, creating a new isotope.

• Isotopes are atoms of the same element that have different atomic masses.– Example: Carbon always has 6 protons. Sometimes

it has 6 neutrons, sometimes it has 8 neutrons.– Thus, Carbon (mass 12) and Carbon (mass 14) are

isotopes.

Famous Isotopes: 235U

Famous Isotopes: 14C

http://www.purifiedbyfaith.com/CreationEvolution/Genesis5and11/Images/GeigerCounter.gif

Isotope Names

• Isotopes are often written like this:– Carbon-14 (meaning Carbon with a mass

number of 14).• Or like this:

– C-14 (meaning the same thing)• Or like this:

– 14C (meaning the same thing)

On your worksheets…

• Take 1.1 minutes and try #1, 4, 6, and complete #5.– For #1, leave out Atomic Mass.

Changing Electrons

• Neutral atoms have the same number of protons as electrons, balancing the charges.

• Changing the number of electrons creates an ion.• An ion is an electrically-charged atom and can be positive (+) or

negative (-).• Atoms that lose electrons are called cations and have a positive

charge.• Atoms that gain electrons are called anions and have a negative

charge.

How to Remember

• Cations (positive)– “I like cats” – that’s a positive statement!– CA+ION

• Anions (negative)– A negative ion – anion.

Ions

• If an atom has more electrons than protons, it has a negative charge.

• If an atom has fewer electrons than protons, it has a positive charge.

• Example:– Hydrogen has one proton and one electron. If

we take away an electron, hydrogen becomes positively charged.

Determining Charge

• To figure out the charge on an ion, find the number of protons and electrons.

• Use the following formula:[protons] – [electrons] = CHARGE

• Example:• Lithium (atomic number 3) with 5 electrons:• 3 – 5 = Charge of -2 (Li 2-)

Ions

• Write ions by writing:– Element abbreviation– How positive or negative they are in superscript

• Example: Helium with 4 electrons (instead of 2) is He2-.

• For both negative and positive ions with a difference of one electron, just write + or – appropriately.

Ions

• Example:– Hydrogen normally has 1 electron. If it has no

electrons (positive charge) we would write it as H+.

– If Hydrogen has 2 electrons (negative charge), we would write it as H-.

Building Ions

• Let’s build some ions using the computer:– H+

– Li2+

– C-

– O3-

• The only way to make ions is with electrons.

So, do you get this cartoon?

One last thing…

• You may have noticed that in all of this PowerPoint I only mentioned the term atomic mass once, but I have used the term mass number many times.

• There’s a difference!

Calculating Atomic Mass• By now you know that isotopes are atoms

of the same element with different masses.

• Those masses, calculated by adding protons and neutrons (which each weigh 1 amu), are called mass numbers, and they’re different for each isotope.

H11

H12

H13

How Many p+, e-, n0?

• Determine the number of protons, electrons, and electrons for each isotope:

• C-12 and C-14– C-12: Protons = 6; Electrons = 6; Neutrons = 6– C-14: Protons = 6; Electrons = 6; Neutrons = 8

• O-16 and O-18– O-16: Protons = 8; Electrons = 8; Neutrons = 8– O-18: Protons = 8; Electrons = 8; Neutrons = 10

Atomic Mass

• Atomic mass, however, is the weighted average of all the element’s isotopes’ atomic masses based on their abundance.– It’s not a simple average.

• It’s actually quite like the way your grades are calculated. (remember the 50% / 40% / 10% scale?)

• To learn atomic mass, we’ll first learn how you can calculate your chemistry grade.

• Let me introduce you to Rembrandt Q. Einstein, a student in chemistry.– His test average is 90, quizzes/lab/project average is 100,

homework is 50.• If tests are worth 50%, quizzes (etc) 40%, and

homework 10%, what is Rembrandt’s grade?• 90 * (0.5) + 100 * (0.4) + 50 * (0.1) = 90

First category average

First category weight (decimal)

Second category average

Second category weight (decimal)

Third category average

Third category weight (decimal)

PLUS PLUS EQUALSThe Weighted Average

Atomic Mass: Weighted Averages

Good to Know

• Rembrandt’s weighted average grade is a 90%.

• What’s his “simple average” grade?– 80%.

• The fact that Rembrandt’s most “important” grades are good ones raises his average above what it would have been.

• To calculate atomic mass (remember, it’s a weighted average too), use the same procedure as for your grades.

• Mass of Isotope 1 * Abundance of Isotope 1 (decimal) + Mass of Isotope 2 * Abundance of Isotope 2 (decimal)…

• Let’s try a sample problem.

Atomic Mass: Weighted Averages

• What is the atomic mass of silicon if 92.21% of its atoms have mass 27.977 amu, 4.70% have mass 28.976 amu, and 3.09% have mass 29.974 amu?

• 27.977 (.9221) + 28.976 (.047) + 29.974 (.0309) = ?

• Silicon’s atomic mass is 28.09 amu.

First isotope mass

First isotope abundance (decimal)

Second isotope mass

Second isotope abundance (decimal)

Third isotope mass

Third isotope abundance (decimal)

PLUS PLUS

Atomic Mass: Weighted Averages

• Find the average atomic mass for silver if 51.83% of its atoms have mass 106.905 amu and 48.17% of its atoms have mass 108.905 amu.

• 106.905 (.5183) + 108.905 (.4817) = ?

• Silver’s atomic mass is 107.87 amu.

First isotope mass

First isotope abundance (decimal)

Second isotope mass

Second isotope abundance (decimal)

PLUS

Atomic Mass: Weighted Averages

On your worksheets…

• Complete #1, #7, and the reverse side.

Tonight’s Assignment

• You may work alone or with a partner.• Research two additional scientists in the history

of the development of the atomic model.• Prepare a PowerPoint with a timeline including

scientists from class and that you have researched.– Don’t forget to use your textbook!

• Requirements and rubric posted online!

Now for a lab…

• Get your worksheets – we’re going to start the Isotope Bean Lab!

Closure

• Tonight, try practice problems 21 and 22 on page 116, and practice problems 23 and 24 on page 117.