Unit 3, part c

Atomic Theory

EQ

• How does the instability of an atom relate to its nuclear structure?

GPS

• SC3. Students will use the modern atomic theory to explain the characteristics of atoms.– a. Discriminate between the relative size, charge,

and position of protons, neutrons, and electrons in the atom.

– c. Explain the relationship of the proton number to the element’s identity.

– d. Explain the relationship of isotopes to the relative abundance of atoms of a particular element.

a. bottom, protons + neutrons

b. bottom, protons

c. top, protons + neutrons

d. top, protons

Atomic number is the _____ number and it tells how many ______.

An isotope is an atom with the same number of _______ but a different number of ________.

a. neutrons, protons

b. protons, neutrons

c. protons, electrons

d. electrons, protons

Review• Calculate the atomic mass

1H 12%2H 48%3H 40%

...)100

%()

100

%( 2

2

1

1

amuamuAverageWeighted

Nuclear reactions involve changes in an atom’s ___________ while chemical reactions involve changes with _________________.

a. nucleus, electrons

b. electrons, nucleus

Radioactivity• Chemical reaction involves only an atom’s electrons –

the nucleus remains unchanged• Nuclear reaction involves a change in an atom’s

nucleus (p+ or n0); represented in an nuclear equation (226

88Ra → 22286Rn + 4

2) .

• Nuclear Decay: the transformation of an element into a different isotope of the same element or change into an entirely different element.

• Radioactivity is when unstable substances spontaneously emit radiation; the rays and particles emitted are radiation– 4 types of radiation: alpha, beta, gamma, neutron emission

The reason why atoms undergo radioactive decay is to become unstable.

a. True

b. False

Radioactivity• When there are too many protons vs neutrons,

the positive charges will repel each other causing the atom to be unstable

• Unstable radioactive decay stable

radioactive decay

The following show the correct order of strength of radiation from strongest to weakest.

a. alpha, gamma, beta

b. alpha, beta, gamma

c. gamma, beta, alpha

d. gamma, alpha, beta

Nuclear Reactions

• Alpha Radiation–α; 2 protons & 2 neutrons– Can be stopped with paper (tissue paper)

241 = 237 + 495 = 93 +2

He42

HeNpAm 42

23793

24195

Nuclear Reactions

•Beta Radiation– ß particle– negative charge– Fast moving electron– Electron particle made from neutron decay– Can be stopped with foil (think aluminum foil)

14 = 14 + 06 = 7 + -1

01

01147

146 NC

Nuclear Reactions

• Gamma Radiation– Energy (not matter) released from breaking bonds in

nucleus– Occurs with α or ß radiation– Can be stopped with lead or concrete

238 = 234 + 4 + 092 = 90 + 2 + 0

00

0042

23490

23892 HeThU

Nuclear ChemistryType Symbol Power Shielding

Alpha particle- *made of 2 p & 2 n.

4 4 He

2 2

low Paper & clothing

Beta particle-/e*electron made from neutron decay

0 0

e

-1 -1

medium Metal foil

Gamma ray*no charge

*no mass

*not matter- just EM radiation

0 0

high Lead & concrete

neutron emission

1 n

0

High*unstable

Travels farther- blocked by ≥ 15 cm Pb block.

• Conversion of an atom of one element to an atom of another element is called transmutation.

Half Life-• Time it takes for ½ of radioisotope’s nuclei

to decay

• Each element has a unique half life– Polonium-214 = 163.7 microseconds– Radon-222 = 3.8 days– Carbon-14 = 5730 years– Uranium-238 = 4,460,000,000 years

Half Life- uses

– Used for radioactive dating– Medical procedures (diagnose & treat

disease), trace particle through system (DNA, fertilizers)

Half Life

• Either memorize formula OR– Amount remaining = initial amount x (½ )n

• Where n is the number of half lives that passed

– Amount remaining = initial amount x (1/2)t/T

• t = elapsed time, T = duration of half life (must be in same units!)

• Draw Pictures/ diagram

Half-life = t1/2

Half-lives X Amount left (grams)

0 1/2 100 % of grams

1 1/2 1/2

2 1/2 1/4

3 1/2 1/8

4 1/2 1/16

5 1/2 1/32

6 1/2 1/64

Etc. 1/2 etc.

Practice: Half-life= t1/2

1. 2.00 g of N-13 emits B radiation & decays to O-13 with a ½ life of 10 minutes.

– How long is 3 half-lives?

– 10 min x 3 t1/2= 30 min.

– How many g of the isotope are left after 3 half lives? 2.00 g x ½ x ½ x ½ = 0.25 g left

– or since 3 t1/2 = 1/8, 2.00 g x 1/8= 0.25 g

Practice: T1/2

• The half-life of cobalt-60 is 5.3 years. How much of a 20.0 g sample will remain after 21.2 years?

• 21.2/ 5.3= 4 t1/2

• 4 t1/2 is 1/16

• So, 20.0 g

1. The carbon-14 in a sample of bone has ¼ of its original amount. How old is the bone? (Carbon-14 has a half-life of 5730 years)

2. Only 1/8th of the original dose of radon-222 remains in a test subject. How long ago was the radon introduced into the test subject’s body? (Radon-222 has a half-life of 3.8 days)

3. Barium-139 has a half-life of 43 minutes. How many hours will it take to degrade to 1/32nd of its original amount?

4. Polonium-211 has a half-life of 3.2 days. How long will it take to degrade to 1/128th of its original amount?

5. Cobalt - 60 is used to detect leaks in water lines. It has a half life of 38 hours. It can not be detected by the sensors after it reaches 1/32 of its original amount. How many days do engineers have to test the water lines before the Cobalt –60 is undetectable?

Gas prices keep going up, up, and up….

• The problem now is that cars have to be plug in everyday

Nuclear Fission• Process of one atom breaking down into smaller atoms• splitting nucleus into smaller fragments by bombarding it with

neutrons– Chain reaction, high energy, use control rods to slow reaction– Uses: bombs, nuclear power

• http://lectureonline.cl.msu.edu/~mmp/applist/chain/chain.htm

• Biggest problem with nuclear power is the nuclear waste

• Currently, the depleted uranium is stored underground in Yuma, Arizona.

Nuclear Fusion• Fusion is the process of combining 2 smaller atoms

into one larger atom w/ a grater mass• Produces 10 times more energy than fission

– Lots of E, process too hot to control, – sun

• No nuclear waste!

Recap…• Radiation Penetration

– Alpha α– Beta ß– Gamma γ

• Nuclear power– Biggest problem?

• Waste disposal or nuclear meltdown?

• Fission

• Fusion