group 7 Flashcards
trend electronegativity
decreases
larger atoms so larger atomic radius so increased distance between nucleus and shared pair
increased shielding means e- density in cov bond is further from nucleus
decreased FoA, decreased ability
boiling pints
increases
larger molecules so vdw forces between molecules are stronger
more energy to overcome
trend atomic radius
increases
atoms are larger so there are more e- and the gore more completed energy levels
trend in 1st ionisation energy
decreases
bigger atoms
larger radius
increase shielding
more shells
weaker FoA between.. .
e is more easily lost
increased nuclear charge overcome by these effects
halogen molecules profiles - state, characteristics, colour
fluorine
F2
gas at room temp
yellow
toxic
v reactive
halogen molecules profiles
chlorine
Cl2
toxic
v reactive
gas at room temp
green
halogen molecules profiles
bromine
Br2
toxic
reactive
liquid at rtp
orange
halogen molecules profiles - state, uses, colour
iodine
I2
solid r rto
grey silver black
sublimes straight to gas, purple - why?
Van der Waals forces that link iodine molecules together in a crystal are relatively weak. That is why iodine usually sublimes very easily (that is, passes directly from the solid to the gaseous state) without going through the liquid state.
uses: tests for starch
stains cells
antiseptic solution
reaction of chlorine with water (no sunlight)
importance of product
Cl2 + H2O (reversible) HCl + HClO
HClO is chlorate acid which dissociated to produce H+ and ClO- ions
ClO- is a powerful oxidising agent which kills bacteria BC if oxidises things in bacteria
uses as
- water treatment
- food disinfectant
- wound treatment
—
products also written as 2H+ + Cl- + ClO-
reaction of chloride and water (sunlight)
Cl2 + H2O – 4Hcl + O2
not good bc no HClO
so need to replenish regularly in pools
reaction of chlorine and sodium hydroxide
conditions
uses
Cl2 + NaOH – NaCl + NaClO + H2O
conditions: cold, dilute, aq NaOH
NaClO = sodium chlorate - bleach therefore uses as
- cleaning agent
- disinfectant
- cleaning agent
- waste water treatment
what is the trend in oxidising ability of the halogens
explain
decreases
oxidising agent undergoes reduction so it gains e-.
because as go down there are more completed energy levels resulting in increased shielding and atomic radius,
eFoA is weaker between nucleus and e to gain so it’s harder to gain
outline a test you can use to prove the oxidising ability of halogens
- In a spotting tile put Cl2, BR2, and I2 in each row
- put H2O in one column (control)
- KCl in one column
- KBr in one column
- KI in one column
- the more powerful oxidising agent will displace the other halide in the metal halide
- Cl2 displaces Br and I
- in Cl2 with KBr or KI, goes from colourless to orange// brown showing Br2//I2 formed - Br2 displaces I not Cl
- in BR2 with KCl there is no change, remains colourless
- with KI goes from colourless to brown showing I2 formed - I2 doesn’t replace Br and Cl, remains brown (?)
ionic equations for oxidising ability of halogens
Cl2 + 2Br- – 2Cl- + Br2
etc etc (symbols all aq)
trend and explanation of reducing power of halide ions
increases as go down
outer e- being lost (is a 1- ion so has an extra electron. losing it makes them atoms) is further from nucleus due to ions getting bigger so more completed energy levels. increased shielding. so weaker eFoA so e- is more easily lost
reducing power = reducing agent, gets oxidised so losing e-