Sodium, Na. Gallium, Ga. CHEMISTRY 1000. METALS. NONMETALS. Topic #2: The Chemical Alphabet Summer 2007 Dr. Susan Lait. METALLOIDS. Forms of Carbon. The Halogens (Group 17). What is a halogen? Any element in group 17 (the only group containing
Topic #2: The Chemical Alphabet
Dr. Susan Lait
Forms of Carbon
solids, liquids and gases at room temperature)
acids; HF is one of the stronger weak acids
What is a halogen?
Only forms one monoatomic anion (-1) and no free cations
Has seven valence electrons (valence electron configuration [N.G.] ns2 np5) and a large negative enthalpy of electronic attraction
A good oxidizing agent (good at gaining electrons so that other elements can be oxidized)
The oxygen produced in these reactions is particularly reactive, so moist chlorine gas is a much stronger oxidizing agent than anhydrous chlorine – as evidenced by the fact that it can bleach dyes like indigo, litmus and malachite green while anhydrous chlorine cannot.
*See http://boyles.sdsmt.edu/pwithcl/reaction_of_white_phosphorus_and.htm for a video
of the reaction between phosphorus and chlorine at room temperature.
These are disproportionation reactions because one oxidation state of chlorine (Cl2) reacts to give two different oxidation states of chlorine (Cl- and an oxoanion).
(Note that oxidation states are assigned similarly to formal charge, but treating every bond as 100% ionic, so that both electrons in the bond go to the more electronegative atom.)
e.g. HCO3- is “bicarbonate” or “hydrogen carbonate”
*Phosphorous acid is an exception to this rule. Only two of its hydrogens are attached to oxygen.
Where the oxoacid has the formula OpE(OH)q. For oxoacids with multiple protons (i.e. q>1), the pKa increases by ~5 every time H+ is removed (until none remain).