halogens (grp 7) Flashcards
what do halogens exist as
diamonic molecules
appearance of fluorine
yellow gas
appearance of chlorine
green gas
appearance of bromine
brown liquid
appearance of iodine
grey crystalline solid
explain the increase in atomic radius down the group
more shells
shielding increases
more electrons
the pull the outer electrons feel from the nucleus is weaker with increasing number of shells
define electronegativity
power of an atom to attract 2 electrons in a covalent bond
explain electronegativity down the group
decreasing - larger atomic radius, more shells, more shielding, weaker attraction
explain the trend in melting point and boiling point down the group
as molecules become larger they have more electrons and so have larger vdw forces between molecules
more energy needed to break these forces
increases melting and boiling point down the group
solubility of halogens
halogens are poorly soluble in water. halogen molecules are non-polar and cannot form bonds with hydrogen bonds with water molecules
what are halogens soluble in?
organic compounds
colour of chlorine in water and in organic solvent
light yellow, pale yellow-green
colour of bromine in water and in organic solvent
orange, red-brown
colour of iodine in water and in organic solvent
brown, purple
halogens trend in bond strength
decreases bc atomic radius increases
what is bond enthalpy
heat needed to break one mole of a covalent bond
why does fluorine have such low bond enthalpy
because fluorine is so small that the lone pairs get so close and cause repulsion counteracting the attraction between the bonding pair of electrons and two nuclei.
why do you think no value for solubility is assigned to fluorine
reacts too violently to water
how do halogens react with metals
by accepting an electron from the metal atom to become an ion with 1- charge
how are halogens oxidising agents
halogens oxidise the metal by removing an electron from the metal
halogens become reduced as they gain the extra electron
trend in oxidising power in halogens
decreases going down the group as their ability to attract electrons decreases due to shielding
how do halide ions act as reducing agents
they get oxidised and lose electrons
trend of reducing power of halide ions
they increase going down the group because atoms are more bigger with more shielding so its easier to lose an electron
reaction of fluorine and chlorine with sulfuric acid
not strong enough to reduce s in h2so4
one sodium halide that will reduce concentrated sulfuric acid
NaI (sodium iodide)
one way H2S can be recognised
smell of rotten eggs
one way to recognise sulfur
yellow solid
a reagent which could be used to show the reducing ability of bromide ions is diff to chloride ions
sulphuric acid
equation for dilute aqueous sodium hydroxide and chlorine & uses
CL2 + NaOH -> NaCl + NaOCl + H2O
- bleach
- kills bacteria
equation for chlorine being added to drinking water
Cl2 + H2O -> HCl + HClO
why is chlorine added to drinking water & name a disadvantage
- kills bacteria
BUT - may cause eye irritation
- taste bad
equation for phosphorus TRU bromide
6Br2 + P4 -> 4PBr3
test a sample of water to show it contains chloride ions
silver nitrate
it would show white precipitate
In terms of electron transfer, what is the meaning of oxidising agent
electron acceptor
State what you would observe when chlorine gas is bubbled into an aqueous solution of potassium iodide.
brown solution
Identify two sulfur-containing reduction products formed when concentrated sulfuric acid oxidises iodide ions
S & SO2
Describe what you would observe when aqueous silver nitrate is added to separate aqueous solutions of potassium fluoride and potassium bromide
KF - no change
KBR - cream precipritate
Explain why bromine does not react with aqueous chloride ions
because Br2 is a weaker oxidising agent
Write an equation to show how solid potassium fluoride reacts with concentrated sulfuric acid.
KF + H2SO4 -> KHSO4 + HF
reaction of iodine with concentrated Sulfuric acid
1) H2SO4 + 2NaI -> HI + NaHSO4
2) H2SO4 + 2HI -> I2 + SO2 + H2O
3) 6HI + H2SO4 -> 3I2 + S + 4H2O
4) 8HI + H2SO4 -> 4I2 + H2S + 4H2O
