Nuclear Chemistry. Nuclear Reactions Chemical reactions What can NOT change in a chemical...

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Nuclear

Chemistry

Nuclear

Chemistry

Nuclear ReactionsNuclear ReactionsNuclear ReactionsNuclear Reactions

Chemical reactions What can NOT change in a chemical

reaction?Nuclear Reactions: changes that occur in

the nucleus of an atom The nucleus is unstable!!

Most atoms have unstable nuclei.

Why are some stable, while others Why are some stable, while others are not?are not?

Primary Reason: ratio of the neutrons

to the protons (n/p) An atom is most stable

when ratio is 1:1 The maximum ratio of

stability is around 1.5 : 1

RadioactivityRadioactivityRadioactivityRadioactivity

An unstable nucleus emits rays and particles, called radiation, to become stable The process is called

radioactivity Gain stability by

LOSING energy Discovery dealt a

deathblow to Dalton’s theory of indivisible atoms

Types of RadiationTypes of RadiationTypes of RadiationTypes of Radiation

Alpha particle () helium nucleus

paper2+

Beta particle (-) electron e0

leadGamma ()

high-energy photon0

3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles3 Radioactive Particles

1. Alpha Particle (+) It travels about 1/10 the speed of light

(slowest)

• It is the largest, most massive particle

It is the most dangerous if ingested It has the least penetrating ability -

paper can stop this particle

2. Beta Particle (-) Fast accelerated electron Ejected when a neutron is converted to a

proton in the nucleus Travels 1/4 the speed of light. It is lighter and faster than the alpha

particle. Average penetrating ability - can be

stopped by heavy clothing

3. Gamma Ray Not a particle; it is high energy

electromagnetic radiation Has no mass and no charge. Always accompanies either beta or alpha

radiation. Travels at the speed of light. Highest penetrating ability - can be stopped

by heavy shielding such as lead.

Radioactive Particles Radioactive Particles SummarySummary

Alpha Particle

Positive Charge

Mass of a

Helium nucleus

1/10 the speed of light

Beta particle

Negative Charge

Mass of an

electron

1/4 the speed of light

Gamma ray

No charge

No Mass

Speed of Light, c

Nuclear DecayNuclear DecayNuclear DecayNuclear Decay

Alpha Emission

He Th U 42

parentnuclide

daughternuclide

alphaparticle

Numbers must balance!!

Beta Emission

A neutron is converted in the nucleus of an atom

A new atom is formed whose atomic number is increased by 1

e Xe I 0-1

epn 01

Gamma Emission Always accompanies alpha and beta

emissions.Transmutation

One element becomes another.

Half-lifeHalf-lifeHalf-lifeHalf-life

Half-life (t½) Time required for half the atoms of a

radioactive nuclide to decay. Shorter half-life = less stable.

So, what does this So, what does this mean?mean?

Let’s say you have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. How many grams are left after one half-

life? How many grams are left after two half-

lives?

Common RadioisotopesCommon RadioisotopesCommon RadioisotopesCommon Radioisotopes

Isotope Half-Life Radiation Emitted

Carbon-14 5,730 years

Radon-222 3.8 days

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

Half-lifeHalf-lifeHalf-lifeHalf-life

r (0.5)ni

r : final massi : initial massn : # of half-lives

To find the remaining amount…

More Half-Life EquationsMore Half-Life EquationsMore Half-Life EquationsMore Half-Life Equations

Total time passed (p) = n x t1/2

To find the half-life t1/2 =

To find the # of half lives that have passed… n =

Half-lifeHalf-lifeHalf-lifeHalf-life Fluorine-21 has a half-life of 5.0 seconds. If you

start with 25 g of fluorine-21, how many grams would remain after 60.0 s?

GIVEN:

t½ = 5.0 s

i = 25 g

p = 60.0 s

n = 60.0s ÷ 5.0s =12

r = i (0.5 )n

r = (25 g)(0.5)12

r = 0.0061 g

You try it!You try it!You try it!You try it!

If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?

FF issionissionFF issionission

splitting a nucleus into two or more smaller nuclei

1 g of 235U = 3 tons of coal

U23592

FF issionissionFF issionission

chain reaction - self-propagating reaction

FusionFusionFusionFusioncombining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain1 g of fusion fuel =

20 tons of coaloccurs naturally in

Nuclear Chemistry. Nuclear Reactions Chemical reactions What can NOT change in a chemical...

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