nuclear chemistry fusion and fission. nuclear fission the splitting of a nucleus into smaller...

Nuclear ChemistryFusion and Fission

Nuclear Fission

• The splitting of a nucleus into smaller fragments is called nuclear fission.

• Heavy atoms (mass number>60) tend to break into smaller atoms, thereby increasing their stability.

• Nuclear fission releases a large amount of energy.

Nuclear Fission

U23592n

1 0

The Fission Process

A neutron travels at high speed towards a uranium-235 nucleus.

U23592n

1 0

A neutron travels at high speed towards a uranium-235 nucleus.

The Fission Process

U23592n

1 0

A neutron travels at high speed towards a uranium-235 nucleus.

The Fission Process

U23592n

1 0

The neutron strikes the nucleus which then captures the neutron.

The Fission Process

U23692

The nucleus changes from being uranium-235 to uranium-236 as it has captured a neutron.

The Fission Process

The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process

The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process

The uranium-236 nucleus formed is very unstable.

It transforms into an elongated shape for a short time.

The Fission Process

It then splits into 2 fission fragments and releases neutrons.

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

The Fission Process

It then splits into 2 fission fragments and releases neutrons.

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

The Fission Process

It then splits into 2 fission fragments and releases neutrons.

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

The Fission Process

It then splits into 2 fission fragments and releases neutrons.

14156Ba

9236Kr

n 1 0

n 1 0

n 1 0

The Fission Process

Energy

Nuclear Fission Examples

U235

92 +Ba141

56+ n1

03n

1

0 +Kr 92

36

U235

92 +Cs138

55+ n1

02n

1

0 +Rb 96

37

Review: Balancing Nuclear Equations

• Mass numbers and Atomic numbers must add up on both sides of the reaction arrow.

•100Fm 54Xe + ____ + 4 0n256 140 1

For Atomic numbers 100 = 54 + X X = 46

For Mass Numbers: 256 = 140 + X + 4 X = 112

46Pd112

18

White Boards

Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction.

1n + 235U 137Te + ?X + 2 1n + energy0 92 52 ? 0

19

Solution

1n + 235U 137Te + 97Zr + 2 1n + energy0 92 52 40 0

Fission Chain Reactions• One fission reaction can lead to more

fission reactions in a process called a chain reaction.

• Example - The fission of Uranium-235

Chain Reaction of Uranium-235

• A chain reaction can only occur if the starting material has enough mass to sustain a chain reaction. This amount is called the critical mass.

• Nuclear Fission is what occurs in Nuclear Reactors and Atomic Bombs.

• The Nuclear reactor is a controlled fission reaction, the bomb is not.

• The chain reaction releases a large amount heat and energy that produces an atomic explosion.

Nuclear Fusion• The combining of atomic nuclei to form a larger

atom is called fusion• Nuclear fusion occurs in the sun when two nuclei

with low mass numbers combine to produce a single nucleus with a higher mass number.

• Fusion releases large amounts of energy.• Example:

4 H + 2 0 e He + energy1

1

-1 2

4 Energy

Nuclear Fusion

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

H 2 1

H 3 1

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

The Fusion Process

He 4 2

n 1 0

ENERGY

Nuclear fusion is what powers our sun - and all stars.

And also - Hydrogen Bombs

Fusion• Fusion reactions also release very large

amount of energy but require extremely high temperatures to start.

• Nuclear fusion also occurs in new stars and is how all of our elements were made.

He + He Be + energy42 2

4 84

He + Be C + energy42

84

126

Other Fusion Reactions

• Hydrogen Bomb or possible Fusion nuclear reactor reaction

• 3H + 2H 4He + 1n

• New elements discovered:• 20Ca + 95Am 115Uup

•115Uup 113Uut + 2He

1 1 2 0

4

Remember:Nuclear fission and fusion

both occur with an incredible release of energy.

Energy

Indicate if each of the following describes

1) nuclear fission or 2) nuclear fusion.

___ A. a nucleus splits.

___ B. large amounts of energy are released

___ C. small nuclei form larger nuclei.

___ D. hydrogen nuclei react.

___ E. several neutrons are released.

Learning Check

44

Indicate if each of the following is

1) nuclear fission or 2) nuclear fusion.

1 A. a nucleus splits.

1, 2 B. large amounts of energy are released.

2 C. small nuclei form larger nuclei.

2 D. hydrogen nuclei react.

1 E. several neutrons are released.

Solution

Chemical Reactions

• Involve changes in electrons– Acids & Bases,

combustion, displacement

• The same atoms appear on both sides of the reaction.

• Small amount of energy generated– Burning fossil fuels

Nuclear Reactions

• Involve changes in the nucleus– Nuclear fusion, nuclear

fission

• New atoms appear as products of the reaction.

• Large amount of energy generated – 1 million times more than

chemical reactions– Nuclear fusion on the sun– Nuclear fission for reactors

Decay vs. Nuclear Reactions• Alpha, beta, and gamma

decay occur as ONE atom tries to increase it’s stability by getting rid of a few neutrons, or protons & neutrons.

• The product is an alpha, beta, or gamma particle and ONE new atom. There is only ONE thing on the left hand side.

• Nuclear reactions involve more than just getting rid of a few protons or neutrons. The new atoms produced are VERY different elements than the reactant.

• Nuclear reactions must be started, so there are 2 things on the left hand side.– Nuclear fission: makes 2

or more much smaller atoms

– Nuclear fusion: makes 1 much larger atom

Nuclear Fission

What are the differences between the 2 above nuclear equations??

Alpha Decay