3.1 Elements, bonding, and physical properties

What are chemical reactions?

• Involve rearrangements of valence electrons (sharing, donating, or accepting)

• The element does not change

What are nuclear reactions?

• Involve changes in the nucleus (not electrons)

• Often result in a change in element (since elements are define by the number of protons)

Fusion in nuclear reactions

Fusion is the process of adding two nuclei together to form a larger nucleus, releasing energy.

Example: Occurs in stars, like the Sun, where hydrogen nuclei fuse to form helium.

Fission in nuclear reactions

Fission is the process of breaking apart a nucleus into two smaller nuclei, releasing energy.

Example: Used in nuclear power plants, where uranium nuclei split to produce energy.

Radioactive decay in nuclear reactions

Radioactive decay is the process of emitting particles (such as α, β, γ) from the nucleus of an unstable atom, leading to a change in the atom

Example: Uranium-238 decays into thorium-234 by emitting an alpha particle (α).

A

A

B

C

Before fusion: Potential energy increases due to electrostatic repulsion as the nuclei approach.

After fusion: Potential energy decreases sharply as the strong nuclear force takes over and the nuclei fuse.

A

B

Nuclear fission

Nuclear fission is the fragmentation of heavy nuclei into lighter, more stable ones, releasing energy in the process

Chain reaction in nuclear fission

Process: Neutrons released in the fission of 235U can induce three more fissions, which then induce nine more, and so on, creating a chain reaction.

Critical mass in nuclear fission

Critical mass is the minimum mass of material required for the chain reaction to become self-sustaining.

Radioactivity

Radioactivity occurs when a nucleus emits or captures particles or energy in the form of electromagnetic radiation.

Alpha Particle Emission

Type: Alpha particle emission

Description: The nucleus emits an alpha particle (2 protons and 2 neutrons)

Beta Particle Emission

Type: Beta particle (electron) emission

Description: A neutron decays into a proton, emitting a beta particle (electron).

Positron Emission

Type: Positron emission

Description: A proton decays into a neutron, emitting a positron (the electron’s antimatter counterpart)

Electron Capture

Type: Electron capture

Description: An inner orbital electron is captured by the nucleus, where it combines with a proton to form a neutron

Gamma Radiation

Type: Gamma radiation

Description: Electromagnetic radiation is emitted from the nucleus, typically following other types of decay.