Group 17 elements - general properties - class-XII

Down the group $e^-$ affinity decreases due to increase in size. Here $I$ having large size has least $e^-$ affinity.

From the electronic configuration given it is clear that element M is 1 short of octet configuration. It belongs to group 17. Group 17 elements exist as diatomic molecules.

Because electronegativity decreases down the group thereby $e^-$ attracting tendency decreases down the group. $F$ with high electronegativity will have strongest bond and $I$ with least electronegativity will have least bond strength.

$F _2$ has lower bond dissociation energy than $Cl _2$ due to its small size and high electronegativity.

$e^-$ affinity of $F$ is less than that of $Cl$ because of the small size and high electronegativity of $F$ it repels the incoming $e^-$ thereby decreasing its $e^-$ affinity whereas $Cl$ having bigger size than $F$ & can accommodate the new incoming extra $e^-$.

$H _2SO _4$ is used in storage batteries.

Group 17 is also called halogen family.

According to Fajan's rules, larger cations and smaller anions favor covalent character, while smaller cations and larger anions favor ionic character. Sodium chloride (NaCl) has a smaller anion compared to fluorides, making it relatively less ionic among the given alkali halides.

I2Cl6 exists as a dimer of ICl3. The structure is planar with two bridging chlorine atoms and two iodine atoms, where all six atoms (two iodine and four chlorine atoms) lie in the same plane.

In NaOX, X represents a halogen. While NaOF, NaClO, and NaBrO are known compounds, NaOI is extremely unstable and does not exist in standard conditions because iodine is not electronegative enough to form a stable hypohalite ion in this context.

Fluorine $(F _2)$ is a halogen , which is a non-metal and has highest electronegativity, so it has maximum affinity for hydrogen. 

Fluorine has a small size thus it has a high nuclear charge and its electrons are strongly attracted towards the nucleus. Thus it requires high energy for excitation. Among halogen atoms, fluorine requires the highest energy for excitation.

Sea salt $\to$ like $Mgcl _{2},\ MgBr _{2}$ have halogens.  $\therefore$  Halogens are sea salt products

We know that halogens have 7 electrons in their valence shell.

the given reaction is

• Electron Gain Enthalpy is the energy released when one mole of an electron is added to gaseous atoms of an element. 
  
• The correct order of Electron gain enthalpy of Fluorine family is,
  

Let x be the percentage of Cl-37. Then (100-x) is the percentage of Cl-35. The average atomic mass is (37x + 35(100-x))/100 = 35.5. Solving this gives 37x + 3500 - 35x = 3550, so 2x = 50, x = 25%.

Bond dissociation energy with hydrogen decreased down the group so HI is will be the most reactive . HI is more reative because the bond dissociation energy is low due to difference in size of hydrogen and iodine so it can be easily breaked.

The electrophilic addition of halogens to alkenes involves the formation of a cyclic halonium ion intermediate, which explains the anti-addition stereochemistry observed in these reactions.

Oxidation number of $Cl _2O _7$:-

Among the elements of same period the ion with more number of electrons and less number of protons is having more radius.If the number of electrons are same the ion with less number of protons is having more radius.

Due to higher electronegativity, HF doesn't follow such reaction and fluorine doesn't form.

Halogens have little tendency to lose electron. Thus they have very high ionisation enthalpy. Due to increase in atomic size, ionisation enthalpy decreases down the group.

Bond dissociation:
$Cl _{2} > Br _{2}$
Standard electrode potential:
$F>Cl$
Bleaching powder $(Ca(ClO) _{2})$             

As we move down the group chemical reactivity decreases due to decrease in electronegativity

Halogens are most electronegative.

Lime water is calcium hydroxide and is a base so it turns phenolphthalein solution (an indicator) pink.

Fluorine is the most electronegative in halogen family so it has oxidation number of -1 in all its compounds but Cl,Br and I are less electronegative so these elements prepare compounds with oxidation number of +1,+3,+5 and +7.

Electronegativity is a chemical property that describes the tendency of the atom to attract electrons towards itself.

Both Assertion and Reason are true and the Reason is the correct explanation of the Assertion. 

Electron Affinity: decreases down the group. Since the atomic size increases down the group, electron affinity generally decreases$ ( I < Br < F < Cl)$. An electron will not be as attracted to the nucleus, resulting in a low electron affinity. However, fluorine has a lower electron affinity than chlorine.

Germanium forms tetrahalides with all halogens except astatine and forms dihalides with all halogens except bromine and astatine.

As we move down the group the metallic character increases which impart lustrousness to the elements.

As the atomic size of the Florine is less it has more nuclear charge. So it requires more energy to remove the electron from its outer most orbit. So Florine has high ionization enthalpy and as we move down the group size increases nuclear charge decreases hence Ionization potential.

Florine is most electronegative than the other elements of that group because it has less atomic size so it attracts electrons more towards itself (Electronegativity).

The atomic number of elements are 9,17,35,53,85.
Electronic configuration of elements will be
9  = 2,7
17= 2,8,7
35= 2,8,18,7
53=2,8,18,18,7
85=2,8,18,18,32,7
The pattern shows that all elements have 7 electron in their outermost valence shell and all these elements belong to halogens.

Halogens need to lose only one electron to form an anion, and thus, their tendency to form an anion is highest. 

The general electronic configuration of chlorine is $[Ne] 3s^{2} 3p^{5}$

F does not have empty d-orbitals o it show only one oxidation state. In othens electrons can excite to empty d-orbitals and show variable oxidation state

$Br - 35$

Bond energy is inversely proportional to molecular mass as van der wall forces exist  between molecules of halogens
$\therefore$ Bond Energy order:
$Cl _2>Br _2>I _2$

Electrovalency theory (valence band theory) explains two atoms that have an unpaired electron in their orbitals can overlap to give rise to chemical bond and chemical bond nothing but an attractive force between two atoms.

As we move along a period from left to right, number of proton increases and valence shell remains same, so, radius of atom decreases.
Also, as we move down the group, number of valence shell increases, so, size of atom increases so order of radii is F < O < C < CI.

Iodine is a component of almost every living plant and animal. No standard measurements of iodine in food exist because iodine concentrations vary across the world. In general, foods from the sea contain the most iodine, followed by animal foods, then plant foods. Of all foods, seaweed (like kelp), is the most well known and reliable source of natural iodine. Egg and dairy products can also be good sources.

Most active element is Fluorine. The reduction potential of fluorine is very high. Hence, it is extremely reactive in nature. Also F-F bond energy is low (38 kcal/mol). The valence shell electron configuration of fluorine $2s^22p^5$  indicates that it has very strong tendency to take up one electron to attain stable noble gas configuration. Hence, it has high reactivity.

The reason is that the attractive forces between the molecules of these elements increase from top to bottom of the Group.

In iodine, the electrons are so far from the nuclei that the electron clouds can easily distort. The London dispersion forces are strong. So the Iodine is solid.

Hence option A is correct.

$CCl _2F _2$ is called as freons or chloro floro carbons.

As we move down the group of halogens the size of elements increases thereby increasing the Van der Waal forces; hence boiling and melting point of Iodine is more than Fluorine molecule.

Ionic compounds are soluble in water
In AgF  $F^-$ is small onion with high charge density so less polarisation and less covalent character in the whole group of Ag holdies.  AgF is most Ionic in nature.