ChemCh25.ppt

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25.1 Nuclear Radiation >

Chapter 25 Nuclear Chemistry

25.1 Nuclear Radiation

25.2 Nuclear Transformations

25.3 Fission and Fusion

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25.1 Nuclear Radiation >

What makes some types of radiation

more dangerous than other types?

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&

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CHEMISTRY

&

YOU

Lengthy or

frequent exposure

to X-rays can

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25.1 Nuclear Radiation >

Radioactivity

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25.1 Nuclear Radiation >

Radioactivity

In 1896, the French chemist Antoine

Becquerel made an accidental discovery.

• He was studying the ability of uranium salts

that had been exposed to sunlight to fog

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25.1 Nuclear Radiation >

Radioactivity

In 1896, the French chemist Antoine

Becquerel made an accidental discovery.

• He was studying the ability of uranium salts

that had been exposed to sunlight to fog

photographic film plates.

• During bad weather, when Becquerel could not

expose a sample to sunlight, he left the

sample on top of the photographic plate.

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25.1 Nuclear Radiation >

Radioactivity

Two of Becquerel’s associates were Marie

and Pierre Curie.

• The Curies were able to

show that rays emitted by

uranium atoms caused the

film to fog.

• Marie Curie and her

husband Pierre shared the

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25.1 Nuclear Radiation >

Radioactivity

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25.1 Nuclear Radiation >

Radioactivity

Marie Curie used the term

radioactivity

to

refer to the spontaneous emission of rays

or particles from certain elements, such as

uranium.

• The rays and particles emitted from a

radioactive source are called

nuclear

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25.1 Nuclear Radiation >

Radioactivity

Radioactivity, which is also called

radioactive decay, is an example of a

nuclear reaction.

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25.1 Nuclear Radiation >

Radioactivity

Radioactivity, which is also called

radioactive decay, is an example of a

nuclear reaction.

• Nuclear reactions begin with unstable

isotopes, or

radioisotopes

.

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25.1 Nuclear Radiation >

Radioactivity

Radioactivity, which is also called

radioactive decay, is an example of a

nuclear reaction.

• Nuclear reactions begin with unstable

isotopes, or

radioisotopes

.

• Atoms of these isotopes become more stable

when changes occur in their nuclei.

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25.1 Nuclear Radiation >

Radioactivity

Unlike chemical reactions, nuclear

reactions are not affected by

changes in temperature, pressure, or

the presence of catalysts. Also,

nuclear reactions of a given

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25.1 Nuclear Radiation >

Radioactivity

Radioactive decay is a spontaneous

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25.1 Nuclear Radiation >

Radioactivity

Radioactive decay is a spontaneous

process that does not require an input of

energy.

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25.1 Nuclear Radiation >

Radioactivity

Radioactive decay is a spontaneous

process that does not require an input of

energy.

• If the product of a nuclear reaction is

unstable, it will decay too.

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25.1 Nuclear Radiation >

Radioactivity

Radioactive decay is a spontaneous

process that does not require an input of

energy.

• If the product of a nuclear reaction is

unstable, it will decay too.

• The process continues until unstable isotopes

of one element are changed, or transformed,

into stable isotopes of a different element.

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25.1 Nuclear Radiation >

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25.1 Nuclear Radiation >

Why do unstable isotopes undergo

nuclear reactions?

Unstable isotopes undergo nuclear reactions

so that they may be changed, or

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25.1 Nuclear Radiation >

Types of Radiation

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25.1 Nuclear Radiation >

Types of Radiation

Radiation is emitted during radioactive

decay.

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25.1 Nuclear Radiation >

Characteristics of Some Types of Radiation

Type

Consists of

Symbol Charge

Mass

(amu)

Common

source

Penetrating

power

Alpha

radiation

Alpha particles

(helium nuclei)



,

2+

4 Radium-226

Low

(0.05 mm

body tissue)

Beta

radiation

Beta particles

(electrons)



,

1–

1/1837

Carbon-14

Moderate

(4 mm body

tissue)

Gamma

radiation

High-energy

electromagnetic

radiation



0

0 Cobalt-60

Very high

(penetrates

body easily)

He

4

2 e

0 –1

Interpret

Data

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

Some radioactive sources emit

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

Some radioactive sources emit

helium nuclei, which are also called

alpha particles.

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

Some radioactive sources emit

helium nuclei, which are also called

alpha particles.

• Each

alpha particle

contains two

protons and two neutrons and has a

double positive charge.

• An alpha particle is written He or

4 

.

2

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

The radioisotope uranium-238 emits alpha

radiation and is transformed into another

radioisotope, thorium-234.

U

238

92 Uranium-238

Th +

234

90 Thorium-234

He (



emission)

4

2 Alpha particle

Radioactive

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

When an atom loses an alpha particle, the

atomic number of the product is lowered

by two and its mass number is lowered by

four.

• In a balanced nuclear equation, the sum

of the mass numbers (superscripts) on

the right must equal the sum on the left.

• The same is true for the atomic numbers

(subscripts).

U

238

92 Th +

234

90 He

4

2

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25.1 Nuclear Radiation >

Types of Radiation

Alpha Radiation

Because of their large mass and charge,

alpha particles do not travel very far and

are not very penetrating.

• A sheet of paper or the surface of your skin

can stop them.

• But radioisotopes that emit alpha particles

can cause harm when ingested.

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25.1 Nuclear Radiation >

Types of Radiation

Beta Radiation

An electron resulting from the breaking apart

of a neutron in an atom is called a

beta

particle

.

• The neutron breaks apart into a proton, which

remains in the nucleus, and a fast-moving

electron, which is released.

n

1

0 Neutron

p +

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25.1 Nuclear Radiation >

Types of Radiation

Beta Radiation

The symbol for the electron has a subscript

of –1 and a superscript of 0.

• The –1 represents the charge on the electron.

• The 0 represents the extremely small mass of

the electron compared to the mass of a proton.

n

1

0 Neutron

p +

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25.1 Nuclear Radiation >

Types of Radiation

Beta Radiation

Carbon-14 emits a beta particle as it decays and

forms nitrogen-14.

• The nitrogen-14 atom has the

same mass number as

carbon-14, but its atomic

number has increased by 1.

• It contains an additional

proton and one fewer neutron.

C

14

6 Carbon-14

(radioactive)

N +

14

7 Nitrogen-14

(stable)

e (



emission)

0 –1

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25.1 Nuclear Radiation >

Types of Radiation

Beta Radiation

A beta particle has less charge than an

alpha particle and much less mass than an

alpha particle.

• Thus, beta particles are more penetrating than

alpha particles.

– Beta particles can pass through paper but are

stopped by aluminum foil or thin pieces of

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25.1 Nuclear Radiation >

Types of Radiation

Beta Radiation

Because of their opposite charges, alpha and beta

radiation can be separated by an electric field.

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25.1 Nuclear Radiation >

Types of Radiation

Gamma Radiation

A high-energy photon emitted by a radioisotope is

called a

gamma ray

.

• The high-energy photons are a form of

electromagnetic radiation.

• Nuclei often emit gamma rays along with alpha or beta

particles during radioactive decay.

Ra +

226

88 Radium-226

Th

230

90 Thorium-230

He +



4

2 Alpha

particle

Gamma

ray

→

Pa +

234

91 Protactinium

Th

234

90 Thorium-234

e +



0 –1

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25.1 Nuclear Radiation >

Types of Radiation

Gamma rays have no mass and no

electrical charge.

• Emission of gamma radiation does not alter

the atomic number or mass number of an

atom.

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25.1 Nuclear Radiation >

Types of Radiation

Because gamma rays are extremely penetrating,

they can be very dangerous.

• Gamma rays pass easily through paper, wood, and the

human body.

• They can be stopped, although not completely, by several

meters of concrete or several centimeters of lead.

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25.1 Nuclear Radiation >

Gamma rays can be dangerous because

of their penetrating power. What property

determines the relative penetrating power

of electromagnetic radiation?

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&

YOU

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25.1 Nuclear Radiation >

Gamma rays can be dangerous because

of their penetrating power. What property

determines the relative penetrating power

of electromagnetic radiation?

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&

YOU

CHEMISTRY

&

YOU

The wavelength and energy of

electromagnetic radiation determine its

relative penetrating power. Gamma rays

have a shorter wavelength and higher

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25.1 Nuclear Radiation >

Which process involves a radioactive

nucleus releasing a high-speed

electron?

A. oxidation

B. alpha emission

C. beta emission

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25.1 Nuclear Radiation >

A. oxidation

B. alpha emission

C. beta emission

D. gamma radiation

Which process involves a radioactive

nucleus releasing a high-speed

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25.1 Nuclear Radiation >

Key Concepts

Unlike chemical reactions, nuclear

reactions are not affected by changes in

temperature, pressure, or the presence of

catalysts. Also, nuclear reactions of a

given radioisotope cannot be slowed

down, sped up, or stopped.

Three types of nuclear radiation are alpha

radiation, beta radiation, and gamma

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25.1 Nuclear Radiation >

Glossary Terms

• radioactivity:

the process by which nuclei

emit particles and rays

• nuclear radiation:

the penetrating rays and

particles emitted by a radioactive source

• radioisotope:

an isotope that has an unstable

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25.1 Nuclear Radiation >

Glossary Terms

• alpha particle:

a positively charged particle

emitted from certain radioactive nuclei; it

consists of two protons and two neutrons and

is identical to the nucleus of a helium atom

• beta particle:

an electron resulting from the

breaking apart of neutrons in an atom

• gamma ray:

a high-energy photon emitted by

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25.1 Nuclear Radiation >

Electrons and the Structure of Atoms

• Unstable atomic nuclei decay by emitting

alpha or beta particles.

• Often gamma rays are emitted too.

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25.1 Nuclear Radiation >

END OF 25.1