4.2 Flashcards
why are group 7 elements called halogens
they all form halide salts
why are fluorine & astatine often ignored
fluorine often behaves differently
astatine only exists as a radioactive isotope
are halogen molecules polar
no
summarize london forces
electron density continuously fluctuates due to movement
sometimes + & - charges don’t coincide
creating an instantaneous dipole
which induces a dipole on a nearby molecule
so there is a force of attraction between the molecules
what is group 7s trend in mp & bp
increases down the group
why do the halogens mp’s & bp’s increase down the group
more electrons
stronger instantanious dipole
stronger forces of attraction
require more energy to overcome
define electronegativity
the ability for an atom to attract a bonding pair of electrons in a covalent bond
why do group 7 have the highest electronegativity
big nuclear charge
short distance between nucleus and bonding pair
less shells therefor less shielding
which element has the highest electronegativity
fluorine
what is the trend in reactivity for the halogens
decrease down the group
why does reactivity decrease down group 7
electronegativity decreases down group (increased shielding, increased atomic radius)
where on the periodic table do the most vigorous reactions occur
bottom of group 1 & 2
top of group 7
what do ionic solids usually look like
white
how can you view the different colours of aqueous chlorine, iodine & bromine
add an organic solvent such as cyclohexane after the reaction as they will dissolve in organic layer and can be seen more easily
what colour is aqueous
-chlorine
-bromine
-iodine
chlorine - pale green
bromine - orange
iodine - purple
why does reactivity decrease down group 7
top of group have smallest atomic radius so closer to proton therefor experience stronger force of attraction
less shells therefor proton experiences the least repulsion
what is the half equation for reduction of halide ions
X2 + 2e- -> 2X-
what is the equation for the partial ionization of sulfuric acid
H2SO4 <=> H+ + HSO4-
what is produced & observed when concentrated H2SO4 reacts with NaBr
misty brown fumes
choking smell
hydrogen bromide, bromine & sulfur dioxide
what is produced & observed when concentrated H2SO4 reacts with NaCl
misty fumes
hydrogen chloride
what is produced & observed when concentrated H2SO4 reacts with NaI
misty purple fumes, choking smell, yellow solid,
rotten egg smell
hydrogen iodide, sulfur, iodine. sulfur dioxide, hydrogen sulfide
what is the test for halide ions and what solution is added in preparation & why
test - silver nitrate solution
nitric acids must be added to ensure any other anions are removed
what are the positive results for
-chlorine
-bromine
-iodine
in the halide ions test
chlorine - white precipitate
bromine - cream precipitate
iodine - yellow precipitate
which ions out of chloride, bromide and iodide are soluble in dilute aqueous ammonia
chlorine
which ions out of chloride, bromide and iodide are soluble in concentrated aqueous ammonia
chlorine
bromine
how do halides react with water
react readily
form acidic colourless solutions
how do halides react with ammonia
all halides react
form a salt in the form of a white solid
