P block - 17 and 18 Flashcards
which is the major noble gas in the atmosphere
argon
which is the main commercial source of helium
natural gas
how was oganesson synthetically produced
collision of Cf atoms and Ca ions
What is the trend of ionisation enthalpy
generally decreases down the group
Which element in group 18 has largest ionisation enthalpy
Neon
Why do noble gases have low bp and mp
the only interaction in these elements is weak dispersion force
What is the colour of O2(+)PtF6(-)
Red
Why was Xe(+)PtF6(-) made
same first ionisation enthalpy as oxygen
What are the three fluorides xenon forms
XeF2, XeF4, XeF6
What are the conditions required to form xenon fluorides
for XeF2 - 673K, 1 Bar
XeF4 - 873k, 7Bar
XeF6 - 573K, 60-70 Bar
What happens when XeF4 and O2F2 interact at 142 K
XeF6 is formed
What are the structures of xenon fluorides
XeF2 - linear
XeF4 - square planar
XeF6 - distorted octahedral structure
How to prep XeO3 and what are its properties
Hydrolysis of XeF4 and XeF6 gives XeO3. It is a colourless explosive solid with a pyramidal molecular structure
How to prep XeOF4 and what are its properties
partial hydrolysis of XeF6 . Colourless volatile liquid with a square pyramidal structure
Does the hydrolysis of XeF6 lead to a redox reaction
No, the products are XeOF4 and XeO2F2 where the oxidation states of all elements remain the same
What is the trend of electron gain enthalpy in group 17
FBr>I . F is small - interelectronic repulsion
What are the trend of melting and boiling points
increase down the group
What are the colours of different halogens
F2- yellow, Cl2- greenish-yellow, Br2 - red, I2- violet
Comment on the solubility of group 17
F and Cl react with water. Br and I are sparingly soluble in water. They react with organic solvents like chloroform, CCl4, carbon disulphide and hydrocarbons to give coloured solutions
What is the trend for oxidising ability in group 17
they are oxidising agents because of their tendency to accept electrons. F2 is the strongest oxidising halogen. It decreases down the group.
What happens when halogens react with water
Fluorine oxidises it to Oxygen. cl and br react to form corresponding hydrohalic and hypohalic acids. I + H2O is non-spontaneous. I can be oxidised by O in acidic medium.
What does the oxidising ability of group 17 depend on
Enthalpy of dissociation, electron gain enthalpy, enthalpy of hydration
What are anomalies in F
- only one oxoacid
HF is a liquid ( due to H-bonding) - others are gases - higher ionisation enthalpy, EN, electrode potential
- lower radii, mp, bp, egh, enthalpy of bond dissociation
What is the acidic strength of hydrohalic acids
HF
What is the stability of hydrohalic acids
HF>HCl>HBr>HI due to decrease in bond dissociation enthalpy
What are the oxides of fluorine
OF2 (stable), O2F2
What is the order of stability of oxides of group 17
I>Cl>Br. I has greater polarisability. Cl has multiple bond formation between cl and O due to d orbital. Br lacks both. Higher oxides have more stability than lower ones.
Are oxides of halogens good oxidising agents
Yes, they are very powerful
What is the trend of ionic character of metal halides
MF>MCl>MBr>MI. Higher oxidation state is more covalent than the lower one.
How can Cl2 be prepared
By heating MnO2 with conc HCl ( mixture of NaCl and H2SO4 can be used in place of HCl)
By the action of HCl on KMnO4
How is Cl2 manufactured
Deacons process: oxidation of HCl gas by atmospheric O2 in presence of CuCl2 at 723 K
Electrolytic process: electrolysis of brine. Cl is liberated at anode
What is the reaction of Cl2 with alkalies
cold and dil alkalis - mixture of chloride and hypochlorite
hot and conc alkalies - chloride and chlorate
What is the reaction of Cl2 with hydrocarbons
saturated - substitution products
unsaturated - addition products
What is responsible for bleaching properties of chlorine
Hypochlorous acid - HOCl - gives nascent oxygen
How to prep HCl
NaCl+ H2SO4 at 420K gives NaHSO4 and HCl
NaHSO4 + NaCl at 823K gives Na2SO4 + HCl
What is aqua regia
3 parts HCl and 1 part HNO3
What is the oxoacid formed by fluorine
HOF - fluoric (I) acid or hypofluorous acid
How are interhalogen compounds prepared
Direct combination with specefic conditions
What are properties of interhalogen compounds
- diamagnetic
-volatile solids of liquids (except ClF) - mp and bp are higher than expected
more reactive than halogens (except f)
What are the molecular structures of interhalogen compounds
XX3 has bent T shape
XX5 has square pyramidal
IF7 has pentagonal bipyramidal
