unstable nuclei and radioactive decay section 4.4

Unstable Nuclei and Radioactive Decay

•Section 4.4

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Radioactivity

• Some substances spontaneously emit radiation – radioactivity

• The rays and particles emitted are called “radiation”.

• Radioactive elements change their identity – they can change into another element– They do this because the nuclei are unstable– Changes to atom’s nucleus is called a nuclear

reaction Something else Dalton got wrong.


Radioactive Decay

• Radioactive elements emit energy as radiation

• This is called ‘radioactive decay’

• Unstable atoms undergo radioactive decay until they form stable atoms


Types of Radiation

• Alpha Radiation – emitting a positively charged particle - α

• Beta Radiation – emitting a negatively charged particle - β

• Gamma Radiation – High energy radiation with no mass - γ


Alpha Radiation

• Alpha radiation– Made up of

Alpha particles– Alpha particles

have 2 protons, 2 neutrons

– Alpha particles have a 2+ charge

α


Nuclear Equations

Nuclear Equations transmutation - an element is transformed into a new element. This can occur by natural or artificial means.

loss of an particle radium is emitting an particle

+


Beta Radiation

• Beta Radiation is fast moving electrons– Attracted to positive charged items– Charge is 1-


Gamma Radiation

• High Energy radiation with no mass– No charge– Usually accompany alpha and beta radiation– Account for most of the energy lost during

radioactive decay


What Makes Nuclear Stability?

• Biggest factor is neutron to proton ratio

• Will be discussed in Chapter 25

• Atoms with either too many or too few neutrons will be radioactive


Review

• Explain how unstable atoms gain stability?– Atoms gain stability by losing energy as

emitted radiation.

• Complete the following table:

Particle Symbol Mass (amu) Charge

α

β

γ

42 He0-1 β

00γ

41/1840

0

+2-10


Review

Particle Symbol Mass (amu) Charge

α 4 +2

β 1/1840 -1

γ 0 0

42 He

0-1 β00γ


Review

• Classify each as a chemical reaction, nuclear reaction, or neither

• Thorium emits a beta particle:– Nuclear

• Two atoms share electrons to form a bond:– Chemical

• A sample of pure sulfur emits heat as it slowly cools:– Neither

• A piece of iron rusts:– chemical

unstable nuclei and radioactive decay section 4.4

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