ChemistryChemistry

Chapter 4Chapter 4

Notes #3 (Sec 4)Notes #3 (Sec 4)

Unstable NucleiUnstable Nuclei Nuclear ReactionsNuclear Reactions

– Rxns that involve a change in the Rxns that involve a change in the nucleus of an atom (most only involve nucleus of an atom (most only involve e- changes)e- changes)

Radioactivity Radioactivity – When substances spontaneously emit When substances spontaneously emit

radiationradiation RadiationRadiation

– Rays and particles emitted by Rays and particles emitted by radioactive materialradioactive material

Unstable NucleiUnstable Nuclei

By emitting radiation atoms of By emitting radiation atoms of one element can change into one element can change into atoms of another elementatoms of another element

This happens because the nuclei This happens because the nuclei is unstableis unstable

Atoms gain stability by losing Atoms gain stability by losing energy (ex. Pencil falling over)energy (ex. Pencil falling over)

Unstable NucleiUnstable Nuclei

Unstable nuclei will lose energy Unstable nuclei will lose energy by emitting radiation in a by emitting radiation in a spontaneous process (so it spontaneous process (so it doesn’t require energy) called doesn’t require energy) called radioactive decayradioactive decay

They undergo decay until they They undergo decay until they form stable non-radioactive form stable non-radioactive atoms of a different element.atoms of a different element.

Radiation-AlphaRadiation-Alpha

Positively charged alpha particlesPositively charged alpha particles– Deflected toward a negative plateDeflected toward a negative plate– Alpha particle – 2 pAlpha particle – 2 p++ and 2 n and 2 n00

– Symbol Symbol 4422He or He or αα

Nuclear Equation shows atomic # Nuclear Equation shows atomic # and mass # of the particles involvedand mass # of the particles involved

Ex. Alpha decay- Radium-226 into radon-Ex. Alpha decay- Radium-226 into radon-222222

Radiation - BetaRadiation - Beta

Negatively charged beta particlesNegatively charged beta particles– Deflected toward a positive plateDeflected toward a positive plate

-with a -1 charge-with a -1 charge

– symbol: symbol: 00-1-1ßß

Ex. Carbon-14 into Nitrogen-14Ex. Carbon-14 into Nitrogen-14

Radiation - GammaRadiation - Gamma

Not deflected by electric or Not deflected by electric or magnetic fieldsmagnetic fields

High energy radiation with no High energy radiation with no massmass

accompanies alpha and beta accompanies alpha and beta radiation radiation

Denoted by the symbol: Denoted by the symbol: 0000УУ

Unstable NucleiUnstable Nuclei

Atoms containing too many or too Atoms containing too many or too few neutrons are considered few neutrons are considered unstableunstable

Stability is based on the ratio of Stability is based on the ratio of neutrons to protonsneutrons to protons

The END!The END!