Chem 2 (Group 7) Flashcards
Properties of Group 7 elements
- most reactive non-metals
- 7 electrons in their outer shell
- often form metal halides with Group 1 and 2 metals.
Why are they diatomic?
because they have two halogen atoms are covalently bonded together
How are the molecules held together?
Van der Waals (temporary dipoles) is when the electron density is fairly symmetrical in a molecule but it’s always going to change so one side is going to be slightly more electronegative ($-) which induces a dipole to make a $+ in a neighboring molecule so although this is constantly changing it holds the molecules together.
How does the Van der Waals affect boiling points?
Fluorine is a gas at room temperature because it doesn’t take much energy to overcome the bonds. Chlorine has permanent dipoles so it going to have stronger intermolecular forces but still is a small molecules. Iodine and bromine are larger molecules so have an increased number of Van der Waals and require a lot more energy to break. Iodine is the highest (solid at room temp).
What 2 things decrease as you go down Group 7?
- volatility (tendency to turn into a gas)
- Electronegativity
What is the pattern of electronegativity?
Fluorine is the most electronegative because it is the smallest atom so its nucleus will be close to the other atom’s nucleus with little shielding so the power is going to be strong. Cl has one more shell of electrons so increased shielding from the nucleus, so is going to be slightly less. As the size of the molecule increases, the less electronegative it becomes.
F>Cl>Br>I
Oxidising abilities?
Either they share electrons in a covalent bond or they accept an electron and form a negative ion in an ionic compound like sodium chloride.
Their ability to accept these ions makes them a good oxidising agent.
Order: F2>Cl2>Br2>I2
Chlorine + potassium bromide = ?
Cl2 + KBr > KCl + Br2
Cl2 + 2Br- > 2Cl- + Br2
half equations for Chlorine + potassium bromide = ?
Cl2 + 2e- > 2Cl- (reduced)
2Br- > Br2 + 2e- (oxidised)
Which halogen atoms displace which?
Fluroine displaces all of them
Chlorine displaces bromine
Bromine displaces iodine
Chlorine and bromine displace iodine
If halogen atoms are good oxidising agents.and accept electrons then halide ions?
are good reducing agents and donate electrons
pattern of reducing abiltiy of halide ions down group 7?
Increases down group 7
F- > Cl- > Br- >I-
What are halides?
Halogen compounds with ionic bonding
When sodium halides react with conc. sulfuric acid..?
- sodium hydrogen sulfate
- matching hydorgen halude e.g. HBr-, HCl- ect
H2S04 + KF/NaF
H2S04 + KF > K2S04 + 2HF
no redox reaction
fluorine doesn’t reduce halide ions
H2S04 + NaCl…?
H2S04 + NaCl > NaHS04 + HCl
no redox reaction
Chlorien doesn’t reduce halide ions
H2S04 + NaBr..> 1st reaction
H2S04 + NaBr > NaHS04 + HBr
no redox reaction
H2S04 + NaBr..> 2nd reaction
2Br- > Br2 + 2e-
Bromide ions are oxidised (lose electrons)
S04 (2-) + 2e- > S02
Sulfate ions are reduced (gain electrons)
colour of bromine
yellowy liquid
H2S04 + NaI..? 1streaction
H2S04 + NaI > NaHS04 + HI
no redox reaction
H2S04 + NaI..? 2nd reaction
2HI + H2S04 > S02 + 2H20 + I2
2I- > I2 + 2e- (iodide iions are oxidised-lose electrons)
S04 (2-) + 2e- > S02 (gain electrons-reduced
H2S04 + NaI..? 3rd reaction
6HI + H2S04 > S + 4H20 + 3I2
2I- > I2 + 2e- (oxidised)
S04 (2-) + 6e- > S
H2S04 + NaI..? 4th reaction
HI + H2S04 > H2S + H20 + I2
2I- > I2 2e– (oxidised)
S04 (2-) + 8e- > H2S
products of conc h2S04 and iodide?
- iodine (violent fumes)
- S02 is colourless
- H2S is pungent
Reacion of halide ions with acidified silver nitrate solution?
Ag+ + F- > AgF (water-soluble)
Ag + + Cl- > AgCl ( white precipitate of silver chloride)
Ag+ + Br- > AgBr ( cream precipitate of silver bromide)
Ag+ + I- > AgI (yellow precipitate of silver iodide)
Reactions of halide ions with dilute aqueous ammonia/concentrated aqueous ammonia?
AgF ( no precipitate)
AgCl dissolves in dilute aqueous ammonia
AgBr - sparingly (slightly) soluble in dilute ammonia but dissolves properly in concentrated ammonia (or dissolves slightly)
AgI - insoluble in concentrated ammonia (wyellow precipitate turns white)
Chlorie is used to treat water like in swimming pools (redox reaction to HOCl)…?
Cl2 + H20 > HOCl + HCl
Cl2 + e- > HCl
Cl2 > HOCl + e-
HCl splits into..?
H+ + Cl-
HOCl dissociates into ..?
HOCl (reversible) >< H+ + ClO-
Cl0- (chlorate l ion) and H0Cl (chloric v acid) is useful for..?
killing pathogens
Reaction of chlorine with cold, diluted sodium hydroxide (and ionic equation)
Cl2 + 2NaOH > NaCl0 + NaCl + H20
Cl2 + 2OH- > Cl0- + Cl- + H20
Use of NaCl0?
bleach
Reactions of halide ions with HN03?
AgCl = white ppt AgBr = Cram/white ppt AgI = white precipitate turns yellow again
