NUCLEAR CHEMISTRY

HOW DOES A NUCLEAR REACTOR WORK?

HOW DOES A SMALL MASS CONTAINED IN THIS BOMB CAUSE …THIS HUGE NUCLEAR

EXPLOSION?

Chemical Rxns vs. Nuclear Rxns

• Chemical Rxns involve valence electrons only

• Valence electrons of different atoms are shared OR

• One atom gives & the other atom takes electrons.

• Small energy release

• Nuclear reactions involves the nucleus. Gives off particles

• Protons, neutrons and/or electrons

• Identity of the atom will change

• Large energy release.

RADIOACTIVITY & RADIOACTIVE ISOTOPES

•ISOTOPES OF CERTAIN UNSTABLE ELEMENTS THAT SPONTANEOUSLY EMIT( RELEASE) PARTICLES AND ENERGY FROM THE NUCLEUS. THE ENERGY THAT IS RELEASED FROM THE NUCLEUS OF THE ATOM IS RADIATION.

RADIOACTIVITY

WHEN AN UNSTABLE ATOM DECAYS (decomposes) ENERGY

IS RELEASEd 3 WAYS:

1. ALPHA DECAY

2. BETA DECAY

3. GAMMA RAY

ALPHA PARTICLE

• MADE OF 2 PROTONS AND 2 NEUTRONS• POSITIVELY CHARGED• SLOW AND HEAVY• LOW PENETRATING POWER• STRONGLY IONIZE (PULL ELECTRON FROM)

OTHER ATOMS.• CAN BE WRITTEN AS:

BETA PARTICLE

• HAVE MINUS 1 CHARGE (-1) , SAME AS ELECTRON• FAST AND LIGHT• MEDIUM PENETRATING POWER AND STOPS AT

ALUMINIUM. • IONIZE PARTICLES AS THEY PASS BUT NOT AS STRONGLY

AS ALPHA PARTICLE.• CAN BE WRITTEN AS:

GAMMA WAVES

• THEY ARE NOT PARTICLES, THEY ARE WAVES • NO MASS AND NO CHARGE• HIGH PENETRATING POWER• NEEDS THICK LEAD OR CONCRETE WALL TO

REDUCE PENETRATION.• DOES NOT EMIT PARTICLES, FOR THAT DOES NOT

CHANGE NUCLEUS.• CARRIES AWAY ENERGY.

RADIOACTIVITY – SUMMARY

NUCLEAR DECAY REACTIONS

• SOME ELEMENTS ARE NATURALLY UNSTABLE AND TEND TO

UNDERGO ALPHA-DECAY OR BETA-DECAY TO BECOME MORE

STABLE.

• IN ORDER TO ACHIEVE THIS, CHAIN OF RXNS(ALSO KNOWN AS

SERIES DECAY) OCCURS FOR MOST RADIOACTIVE ELEMENTS.

• FOR EXAMPLE, IT TAKES U-238 14 STEPS OF ALPHA AND BETA

DECAY TO BECOME COMPLETELY STABLE

IDENTIFYING ALPHA DECAY

DURING ALPHA DECAY NUCLEUS SHEDS 2 PROTONS & 2 NEUTRON AS A PACKET CALLED ALPHA PARTICLE.LOSING 2 PROTONS CHANGES THE IDENTITY OF THE ATOM. EX:WHEN URANIUM WITH 92 PROTONS UNDERGOES ALPHA DECAY WILL BECOME THORIUM WITH 90 PROTONS.

IDENTIFYING BETA DECAY

DURING BETA DECAY A NEUTRON TURNS INTO A PROTON AND AN ELECTRON. ELECTRON IS EMITTED AND IS CALLED BETA PARTICLE

BALANCING NUCLEAR DECAY REACTIONS

AlphaDecay

0�휷 -1

Beta Decay

0e-1

DECAY CHAIN OF U-238

• STEP 1: ALPHA DECAY

• STEP 2: BETA DECAY

• STEP 3:

BETA DECAY

• NOW YOU COMPLETE THE REST ………………………

FISSION

• NUCLEAR FISSION: FISSION IS THE PROCESS OF SPLITTING AN

ATOM. IT GETS HIT BY A NEUTRON.

FUSION

• NUCLEAR FUSION:

MULTIPLE SMALL ATOMIC

NUCLEI JOIN TOGETHER TO

FORM A HEAVIER NUCLEUS.

HALF LIFE•WHEN RADIOACTIVE ISOTOPES DECAY, THEY DO SO

EXPONENTIALLY. THEIR RATE OF DECAY IS DETERMINED

THROUGH AN UNDERSTANDING OF HALF-LIFE.

•HALF-LIFE IS THE AMOUNT OF TIME IT TAKES FOR HALF OF AN

ATOM (UNSTABLE ISOTOPE) TO DECAY.

•ATOMS WITH SHORT HALF-LIVES ARE MORE UNSTABLE THAN

THOSE WITH LONG HALF-LIVES.

•Ex: Half- Life of U-235 is 703 million years

Pu-239 has a half-life of 24,100 years Pu-241's half-life is 14.4 years.

HALF LIFE EXAMPLES• RADON-222 DECAYS WITH A HALF-LIFE OF 3.82 DAYS. IF AN

INITIAL SAMPLE OF THE ELEMENT CONTAINS 1000 ATOMS, HOW

LONG WILL IT TAKE FOR THE SAMPLE TO DECAY DOWN TO 125

ATOMS? YOUR TIME MUST ALWAYS START AT 0 DAYS!

• SOLUTION → AMOUNT TIME HALF-LIFE

1000 ATOMS 0 0

500 ATOMS 3.82 50%

250 ATOMS 4.64 25%

125 ATOM 8.46 12.5%

HALF LIFE EXAMPLES• AN INITIAL SAMPLE OF ZINC-61 CONTAINS 215 GRAMS. AFTER

976 DAYS, THE SAMPLE SIZE HAS REDUCED TO 13.4375 GRAMS.

WHAT IS THE HALF-LIFE OF ZINC-61 ATOMS?

• SOLUTION → AMOUNT TIME HALF-LIFE

215 GRAMS 0 DAYS 0

HALF LIFE EXAMPLES• AN INITIAL SAMPLE OF ZINC-61 CONTAINS 215 GRAMS. AFTER

976 DAYS, THE SAMPLE SIZE HAS REDUCED TO 13.4375 GRAMS.

WHAT IS THE HALF-LIFE OF ZINC-61 ATOMS?

• SOLUTION → AMOUNT TIME HALF-LIFE

215 GRAMS 0 DAYS 0

107.5 122 50% 1

53.75 244 25% 2

26.875 488 12.5% 3

13.4375 976 6.25% 4

HALF LIFE EXAMPLES• THORIUM-230 DECAYS WITH A HALF LIFE OF 80,000 YEARS. IF

AN INITIAL SAMPLE HAS A MASS OF 10.00 GRAMS, HOW MUCH

WILL REMAIN AFTER 320,000 YEARS?

• SOLUTION → AMOUNT TIME HALF-LIFE

10 GRAMS ___ (YRS)