Ch. 19 -- Nuclear Chemistry

Discovery of Radioactivity http://www.radiation-scott.org/timeline/table.htm• Radioactivity was first observed in ______by

the French scientist Henri Becquerel. He discovered that Uranium salts would “fog up” a photographic plate.

• In 1898, Marie Curie and her husband Pierre coined the term radiation and radioactivity and went on to discover several new elements: ___________ and ________.

• She went on to win 2 Nobel Prizes: 1903 in Physics & 1911 in Chemistry, but she died of ________ caused by radiation exposure in 1934 at the age of 66.

• Her husband died in 1906 after getting hit by a horse and buggy.

Marie Curie

1896

Polonium Radium

cancer

Nuclear Reactions• Nuclear reactions involve the _________ instead of the

___________ as in a regular chemical reaction.• The instability of the nucleus of a radioactive element

causes the # of protons and neutrons to change.• Some of the ______ can be converted into a

tremendous amount of energy shown by a very famous equation:

E=mc2

Energy = (mass)x(speed of light)2 c= 3.0 x 108 m/s

nucleuselectrons

mass

Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons.

BE + 19F 9 1p + 10 1n9 1 0

Mass defect (∆m) = 9 x (p mass) + 10 x (n mass) – 19F mass

E = mc2E = mc2

∆m (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984

∆m = 0.1587 amu = 2.636x10-28 kg

BE = 2.636x10-28 kg x (3x108 m/sec)2 = 2.37 x 10-11J

23.2

When this atom forms, a tiny When this atom forms, a tiny amount of matter is converted to amount of matter is converted to energy energy

Energy = mass(kg) x [speed of light ]2

Speed of light = c = 300,000,000 m/sec Speed of light = c = 300,000,000 m/sec

This may look small, but it means that when 19 g of flourine forms there is 14,000,000,000 kJ of energy released. That’s the same as burning 285,000 tons of coal!

2.0141 kg

Nuclear Reactions

1.0078 kg 3.0160 kg

3.0160 – (2.0141 + 1.0078) = 0.0059kg

E=mc2

E= 0.0059 x (3.0 x 108)2 = 5.31 x 1014 Joules

What makes a nucleus stable or unstable?• It depends on the p+

and no ratio.

• Z= Atomic # = p+

• A = Mass # = no + p+

• “Nucleons” are just the particles in the nucleus.

•

• ex) 2 He

AZ

Element symbol

4

Chemical vs. Nuclear Reactions

Nuclear Reactions: Radiation• Nuclear reactions release 3 main types of radiation:

– (α) Alpha Particles … ________ nucleus (2 p+ and 2 n0)– (β) Beta Particles… high energy ___________– (γ) Gamma Rays… high energy _________________

radiation

helium electronselectromagnetic

How To Write Nuclear Particles--α Particles … helium nucleus (2 p+ and 2 n0)

2 He --β Particles… high energy electrons

-1 e--γ Rays… high energy electromagnetic radiation

0 γ

-- Positrons…positive charged electrons

1 e

-- Neutrons…neutrally charged particles in the nucleus that contributes to the mass of an atom

0 n

4

0

0

0

1

Balancing Nuclear Reactions• In chemical reactions the elements stay the same. • In nuclear reactions, the elements ________ but the

mass #’s and atomic #’s are ___________.

Alpha Emission

Beta Emission

changeconserved

Alpha Decay

Beta Decay

Another type of nuclear reaction is “electron capture” where an atom “_________” one of its own electrons. absorbs

Positrons: They are just like an electron, but they have a (___) charge instead of a negative charge.+

Types of Decay--Summary

Nuclear Fission• In fission, the nucleus _______ apart.(Fission is

division.)

• Atom bombs and nuclear power plants use fission of U-235 .

splits

Nuclear Fission: Chain Reaction

Detecting Radiation

When the argon gas is hit by a particle, it ionizes and produces a current…“click”.

Nuclear Power

• Currently about _____ nuclear power plants in the U.S. and about _____worldwide.

• _____ of the world’s energy comes from nuclear.

• There are ___ nuclear power plants in Illinois. The closest one to us is in _________.

103

435

17%

6

Clinton

Clinton, IL Nuclear Power Plant

1000 MegaWatt Power Plant Pollution Coal-Fired vs. Nuclear

Nuclear Power Plants• Nuclear power plants use the heat of a controlled nuclear

fission reaction to ______ water that makes steam which turns a _________ and that produces electricity.

boilturbine

Nuclear Power Plant “Disasters”• One possible type of reactor disaster is known as a __________. In such an accident, the fission reaction goes out of control, leading to the emission of great amounts of radiation.

meltdown

• In ______, a much worse disaster struck Russia's Chernobyl nuclear power plant. In this incident, a large amount of radiation escaped from the reactor. Hundreds of thousands of people were exposed to the radiation. Several _______ died within a few days. In the years to come, thousands more may die of cancers induced by the radiation.

1986

dozen

Chernobyl Sarcophagus

Nuclear Fusion• In Fusion, nuclei combine to form a _________ nucleus.

• When the p+ and n0 bind, this releases tremendous amounts of ________.

• Nuclear fusion occurs in the _____ and other stars.

heavier

energy

sun

Spiderman 2—Tritium

• Medicine imaging and tumor treatments

Thyroid imaging using Tc-99

Uses of Nuclear Radiation

Food Irradiation• Food can be irradiated with gamma rays from 60Co or 137Cs.

• Irradiated milk has a shelf life of __________without refrigeration.

• USDA has approved irradiation of _______ and eggs.

3 months

meats

Isotope Half-Life Radiation Emitted

Carbon-14 5,730 years

Radon-222 3.8 days

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

• Radiocarbon Dating--The radioactivity of a sample can be used to determine how _____ it is.• Half-life: The time for ______ of the nuclei to decay.

oldhalf

Half-Life Graph

Half life practice problems• Astatine has a half-life of about 400 minutes.

If you started with 1000 mg of At, how much would you have after 20 hours?

x

1 hour

60 min= 1200 mins

1200 mins / 400 mins =

20 hours

3 Which means “cut in half” 3 times

1000 mg / 2 = 500 mg/ 2 = 250 mg / 2 = 125 mg