What is a radical?

• A species with an unpaired electron looking for a partner
• A stable ion with a full shell
• A molecule that cannot react

What does ultraviolet light do to a chlorine molecule?

• It joins two molecules together
• It splits the molecule into two chlorine radicals
• It removes all the electrons

Which step ends a radical chain?

• Propagation
• Initiation
• Termination, when two radicals meet and pair up

Why does one photon lead to many product molecules?

• Light keeps shining the whole time
• Each propagation turn regenerates a chlorine radical that reacts again
• Termination creates new radicals

Write the first propagation step for methane with chlorine. Which is right?

• Cl radical plus CH4 gives HCl plus a methyl radical
• CH4 plus Cl2 gives two molecules of HCl
• Methyl radical plus CH4 gives ethane plus hydrogen

Further substitution can be avoided, so the flask holds pure chloromethane.

Circle one:   True   False

Why do chlorine radicals from old refrigerants destroy many ozone molecules each?

• Each radical is regenerated in a chain, like propagation above
• Ozone molecules split on their own
• Termination multiplies radicals

A student writes propagation without any dots and says the steps still balance. What is wrong?

• Dots are decoration and can be dropped
• The dots mark the radicals, and without them the mechanism hides the chain carrier
• Dots belong only on stable molecules