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Nuclear Chemistry. “ regular ” chemistry involves only the ELECTRONS in atoms. All the rest of this year we will be studying only “regular” chemistry. “ nuclear ” chemistry involves only the NUCLEUS in atoms. In this chapter (and only this chapter) we will be studying “nuclear” chemistry. - PowerPoint PPT Presentation
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“regular” chemistry involves only the ELECTRONS in atoms
All the rest of this year we will be studying only “regular” chemistry
“nuclear” chemistry involves only the NUCLEUS in atoms
In this chapter (and only this chapter) we will be studying “nuclear” chemistry
Important Reminder!
• Every atom of the same element must have the same number of PROTONS in its nucleus
• For example, for Lithium to be Lithium, it must have 3 protons. An element with only two protons would be He, with 4 protons Be
• If the number of protons in a nucleus changes, the atom becomes a different element!
Remember the alchemists?
• They wanted to change Pb (82 protons) into Au (79 protons)
• To achieve this would have meant removing 3 protons from the Pb atom’s nucleus
• Alchemists would have needed to do NUCLEAR chemistry
Stability of atoms
• All the atoms we have studied so far have been “stable”. That means they stay the same and don’t change into other atoms
• Some atoms are not stable. They tend to “decay” into other atoms.
• Unstable atoms are called RADIOISOPTOPES
Which atoms are unstable?
• The ratio of protons and neutrons in the nucleus determines an atom stability
# of n = # of p(1 to 1 ratio)
Stableatoms
All atoms with more than 83 protons are unstable
Which atoms are unstable?
• All atoms with more than 83 protons
• Some isotopes of atoms with less than 83 protons do not have the right proton to neutron ratio to be stable
Remember! An isotope is an atom with more or less neutrons than other atoms of that same element
What happens when an unstable atom “decays” ?
• It emits (gives off) radiation particles.
This means it is radioactive.
• It makes a new atom that is more stable
Alpha Particles
α Greek letter alpha
It is the nucleus of a He atom (no e-)
with 2 protons, 2 neutrons and
a charge of +2
He42
Beta Particles
β or β Greek letter beta
Like an electron except it comes
out of the nucleus, not the e- cloud
has negligible (no) mass
has a charge of -1
-
Positron Particles
β Greek letter beta
has negligible (no) mass
has a charge of +1
Like an e- (or β) but with a
positive charge
+
When an unstable atom undergoes alpha decay…..
U23592
decays to
Th23190
Uranium-235 Thorium-231 and an alpha particle
+ He42
Parent atom Daughter product radiation
The following unstable atoms decay by emitting an alpha particle
Ra -226
Rn- 222
Th-232
Look in Table N to find other atoms whose decay mode is also an alpha particle
Write the decay equation for:
Ra -226
Step 1: Re-write the atom symbol so it includes both atomic mass and atomic number (look it up!)
Ra22688
Atomic massAtomic number
Write the decay equation for Ra-226:
Step 2: Put the unstable atom on the left side of the decay arrow
Ra22688
Radium -226 decays to
Write the decay equation for Ra-226:
Step 3: Look up decay mode for the atom in Table N and write that after the decay arrow
Ra22688
Radium -226 decays to alpha particle
α42
Write the decay equation for Ra-226:
Step 4: Find the daughter product by conserving mass and charge
Ra22688
Radium -226 decays to alpha and atom X particle
α42 +
22286 X
226 = 4 + 222
88 = 2 + 86
Write the decay equation for Ra-226:
Step 5: Identify the daughter product by looking up its atomic number
in the periodic table
Ra22688
Radium -226 decays to alpha and Radon-222 particle
α42 +
22286 Rn
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