Topic 12 Group 17

Answer these questions.

– List out all the halogens in group 17?

F, Cl, Br, I, At

– What is the properties of halogens?

– nonmetals.

– relatively low melting and boiling points that increase steadily down the group.

– at room temperature, Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.

– all group 17 elements are oxidising agents.

– becomes darkens in colour when down to group.

– What kind of molecules in halogens? What is the forces in halogens? What is the trends of strength of intermolecular forces in halogens?

All the halogens exist as diatomic molecules, F2, Cl2, Br2, I2. van der Waals dispersion forces are the primary intermolecular attractions between one molecule and its neighbors. Covalent bond is for intramolecular forces within a molecule of halogens. Larger molecules farther down the group have more electrons which can move around and form the temporary dipoles that create these forces. The stronger intermolecular attractions down the group require more heat energy for melting or vaporizing, increasing their melting or boiling points.

– Which halogen has the highest melting point?

From the lowest boiling and melting point to the highest, the group in order is fluorine, chlorine, bromine, iodine and astatine, F < Cl < Br < I < At. When move down the group the halogens become darker in colour. For example fluorine is a very pale yellow whereas iodine will be dark purple in colour when it is in a vapour state.
F =  pale yellow , pale = pucat,
Cl =  pale green 
Br = brown
I = dark purple
At = black

 

– In which halogen the dispersion forces are the most strong?

The dispersion forces are strongest for iodine molecules because they have the greatest number of electrons. The relatively stronger forces result in melting and boiling points which are the highest of the halogen group.

– What is the electronegativity of halogens?

In general, electronegativity increases across a period, and decreases down a group. Therefore, fluorine has the highest electronegativity out of all of the elements. It is because fluorine has seven valence electrons, it only needs one more electron to acheive a noble gas configuration (eight valence electrons, octet).
When down group 17, electronegativity decreases.

Halogen, Electronegativity:

Fluorine = 4.0
Chlorine = 3.0
Bromine = 2.8
Iodine = 2.5

– Why are the halogens non polar?

The shape of a molecule and the polarity of its bonds determine the overall polarity of that molecule. The molecule of halogens has no overall polarity, it is non polar. Halogens molecule were completely symmetric, the dipole moment vectors on each molecule will cancel each other out, making the molecule non polar.

A molecule that contains polar bonds, might not have any overall polarity, depending upon its shape. The simple definition of whether a complex molecule is polar or not depends upon whether its overall centers of positive and negative charges overlap. If these centers lie at the same point in space, then the molecule has no overall polarity (and is non polar). If a molecule is completely symmetric, then the dipole moment vectors on each molecule will cancel each other out, making the molecule nonpolar.

– Why are the halogens oxidising agents?

Halogens can acts as strong oxidizing agents because of halogens are highly electronegative and high electron affinity with low dissociation energies and high negative electron gain enthalpies. Halogens take electrons very much readily from other elements and oxidise other elements. Therefore, halogens have a high tendency to gain an electron.
Therefore, they have a high tendency to gain an electron. Hence, they act as strong oxidizing agents.
– Why iodine is weaker oxidising agent than bromine?

Similarly bromine is a more powerful oxidising agent than iodine. Bromine can remove electrons from iodide ions to give iodine and the iodine can’t get them back from the bromide ions formed because of high electronegativity of the elements placed above.

– Why Astatine is weaker oxidising agent than iodine?
Similarly iodine is a more powerful oxidising agent than astatine. iodine can remove electrons from astatide ions to give astatine and the astatine can not get them back from the iodide ions formed because of high electronegativity of the elements placed above.
– Why is iodide a strong reducing agent, but iodine an oxidising agent?
Iodide has a negative charge, I-, which means it holds extra electrons. In the presence of other iodide atoms it can lose the electrons to form stable I2. The lost electrons will be gained by another species which will be reduced making iodide a good reducing agent. On the other hand, Iodine is not the strongest oxidizing agent and does not make other species lose electrons very easily compared to the oxidizing potential of chlorine, bromine or fluorine. The other halogens are able to oxidize iodine anions as well but not vice versa. A nucleophilic attack on I2, I2 acts as an electrophile (form a I+) because it is a polarizable molecule and may accept electrons from the nucleophile becoming reduced therefore acting as an oxidizing agent.
– What is the reactivity reaction between halogens with hydrogen gas?
H2 + F2 –> 2HF (explosive in the dark)
H2 + Cl2 –> 2HCl (explosive when exposed to strong sunlight)
H2 + Br2 –> 2HBr (200oC. Presence of a catalyst)
H2 + I2 <=> 2HI (450oC. Presence of a catalyst).
The reactivity decrease when down to group.
– What is the reactivity of the reaction between astatine with hydrogen gas?
The reaction between astatine and hydrogen is expected to be slower than the reaction between iodine and hydrogen.

– Why does the oxidising power of halogens decrease down the group?

Whenever a halogen is acts as an oxidant in solution, the it converts to a halide ion which is solvated by water molecules. From fluorine to iodine, the ease with which these hydrated ions are formed decreases; therefore, oxidizing ability decreases down the group. Fluorine is such a powerful oxidizing agent that solution reactions are unfeasible. Chlorine has the ability to take electrons from both bromide ions and iodide ions. Bromine and iodine cannot reclaim those electrons from the chloride ions formed.

– Why Astatine is weaker oxidising agent than iodine?

– Which is the strongest reducing agent among hydrogen halide and why?

HF is a weak acid due to its high bond energy. In solution the halide ions act as reducing agents, the strongest ability increases down the group. HI is the strongest reducing agent.

– Why KCl and H2SO4 react to give only HCl (hydrogen halide) but not chlorine, whereas KI and H2SO4 react to liberate iodine (free halogen)?

HBr and HI are powerful reducing agents, and they are also thermodynamically less stable than HCl. HI easily dissociates to H2 and I2 at higher temperatures. And, conc.H2SO4 is a fairly effective oxidising agent in hot condition.
So, when an iodide like KI is heated with conc.H2SO4, the HI formed in the initial stage is easily oxidised to free iodine, and H2SO4 gets reduced to SO2. Similar reactions take place with a bromide also. 2HI + H2SO4 = SO2 + I2 + 2H2O
HCl is only a mild reducing agent, and it is not easily oxidised to free chlorine gas by conc.H2SO4.

– What is the relation enthalpy vaporisation halogens?

Heat of vaporization: the energy required to vaporize one mole of a liquid at a pressure of one atmosphere. It is a measure of the strength of the intermolecular forces between the particles. Heat of vaporisation, Cl2 > Br2 > I2.

– Arrange order of electron affinity of halogens?

The correct order of electron affinity of halogens is CI> F> Br> I. Electron Affinity (decreases down the group). Since the atomic size increases down the group, electron affinity generally decreases (At < 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.
– Why fluorine has a lower electron affinity than chlorine?
Fluorine, though higher than chlorine in the periodic table, has a very small atomic size. This makes the fluoride anion so formed unstable (highly reactive) due to a very high charge/mass ratio. As a result, fluorine has an electron affinity less than that of chlorine.
– Which hydrogen halide is most acidic?
The order of acidic character can be explained in terms of strength of H−X bonds, which is in the order H−I < H−Br < H−Cl < H−F. Since H−I bond is weakest, therefore, HI is the strongest acid. On the other hand H-F bond is strongest, hence it is the weakest acid among all the halogen acids.
The polar nature of the H-X bond is due to the difference in electronegativity between hydrogen and the halogen. The larger the difference the more polar is the bond. Going down Group 17, the electronegativity of the elements decreases.
H = 2.1
I = 2.5
At = 2.2
The difference in electronegativity between H and At (0.1 unit) is less than that between H and I (0.4 unit). The H-At bond is less polar than the H-I bond. The more polar, less acidic. The less polar, more acidic.
– Explain in terms of hydrogen halide, the more polar, less acidic, the less polar, more acidic?
When these compounds act as an acid, an H-X bond is broken to form H+ and X- ions. The more polar this bond, the easier it is to form these ions. Thus, the more polar the bond, the stronger the acid. An 0.1 M HF solution is moderately acidic.
– HF and HCl which is more acidic?
HCl is a stronger acid than HF because fluorine is more electronegative than chlorine.
– HF and HCl which is more polar?
Fluorine is more electronegative than chlorine. Therefore, we would expect an HF molecule to be more polar than an HCl molecule. In addition, hydrogen is less electronegative than either fluorine or chlorine, so in both of these molecules the hydrogen bears the positive charge.
– What makes HAt stronger acid than HI?
Astatine is the last element in Group 17. The size of the astatine atom is the largest among group 17 elements. As a result, the H-At bond longer and weaker than the H-I bond and easier to break compared to the H-I bond. This makes H-At a stronger acid. An acid is a substance that releases H+ unit (basic definition). The easier it is to release the proton(H+) greater is its acidic strength. SO in this particular case HI is the stronger acid because due to the very large difference in the sizes of the two atoms HI is able to release the proton most easily.
– Why HF is a weak acid?
Why Hydrofluoric Acid Is a Weak Acid. Because the hydroxonium ion is attached to the fluoride ion, it isn’t free to function as an acid, thus limiting the strength of HF in water. The FHF- bifluoride anion is stabilized by a strong hydrogen bond between hydrogen and fluorine.
– Why HF is a weak acid than HCl?
HF is a weaker acid because the strength of an acid is determined by how completely that acid will dissociate. Since the bond between HF is stronger than the bond between HCl, HCl will more completely dissociate which makes it a stronger acid.
– Which hydrogen halide is most reactive?
Therefore, HCl is the most volatile when it comes to reactivity. It dissociates 1000 times more than HF does, creating H+ and Cl- ions. TL;DR HCl dissociates into H+ and Cl- ions 1000x more than HF, but HF, despite being a weak acid chemically, is much much much much more dangerous than HCl.
– What are the health impacts of hydrogen halides?
Concentrated hydrogen chloride can be corrosive to the skin, eyes, nose, mucous membranes, and respiratory and gastrointestinal tracts. Inhalation of hydrogen chloride can lead to pulmonary edema. Ingestion can cause severe injury to the mouth, throat, esophagus, and stomach.
– Which is strongest acid?
Carborane. The World’s Strongest Acid. The record-holder used to be fluorosulfuric acid (HFSO3), but the carborane superacids are hundreds of times stronger than fluorosulfuric acid and over a million times stronger than concentrated sulfuric acid.

The following are high-level thinking skills (KBAT) questions designed based on the learning outcomes provided:

12.0 Group 17

12.1 Physical properties of selected Group 17 elements

1. Relate between the colour intensity of Group 17 elements: Cl2, Br2, I2, with their volatility as down the group?

12.2 Reactions of selected Group 17 elements

1. Explain the reason why is it happens towards the trend in the relative reactivities of Group 17 elements when down group, discussion in relation as oxidising agents from Eº values?

2. Explain the order of reactivity of F2, Cl2, Br2, I2 with hydrogen, and compare the relative thermal stabilities of the hydrides?

3. Explain the reactions of chlorine with cold and hot aqueous sodium hydroxide?

12.3 Reactions of selected halide ions

1. Explain and write equations for reactions of Group 17 ions with aqueous silver ions followed by aqueous ammonia;

2. Explain and write equations for reactions of Group 17 ions with concentrated sulphuric acid.

12.4 Industrial applications of halogens and their compounds

1. Describe the industrial uses of the halogens and their compounds as antiseptic, bleaching agent and in black-and-white photography;

2. Explain the use of chlorine in water treatment.

12 Group 17

12.1 Physical properties of selected Group 17 elements

Candidates should be able to:

(a) state that the colour intensity of Group 17 elements: Cl2, Br2, I2, increase down the group;

(b) explain how the volatility of Group 17 elements decreases down the group.

12.2 Reactions of selected Group 17 elements

Candidates should be able to:

(a) deduce and explain the relative reactivities of Group 17 elements as oxidising agents from Eº values;

(b) explain the order of reactivity of F2, Cl2, Br2, I2 with hydrogen, and compare the relative thermal stabilities of the hydrides;

(c) explain the reactions of chlorine with cold and hot aqueous sodium hydroxide.

12.3 Reactions of selected halide ions

Candidates should be able to:

(a) explain and write equations for reactions of Group 17 ions with aqueous silver ions followed by aqueous ammonia;

(b) explain and write equations for reactions of Group 17 ions with concentrated sulphuric acid.

12.4 Industrial applications of halogens and their compounds

Candidates should be able to:

(a) describe the industrial uses of the halogens and their compounds as antiseptic, bleaching agent and in black-and-white photography;

(b) explain the use of chlorine in water treatment.

12 Group 17

12.1 Physical properties of selected Group 17 elements

 

 

 

 

Candidates should be able to:
(a) state that the colour intensity of Group 17 elements: Cl2, Br2, I2, increase down the group;

(b) explain how the volatility of Group 17 elements decreases down the group.

12.2 Reactions of selected Group 17 elements

Candidates should be able to:
(a) deduce and explain the relative reactivities of Group 17 elements as oxidising agents from Eº values;

(b) explain the order of reactivity of F2, Cl2, Br2, I2 with hydrogen, and compare the relative thermal stabilities of the hydrides;

 

(c) explain the reactions of chlorine with cold and hot aqueous sodium hydroxide.

12.3 Reactions of selected halide ions

Candidates should be able to:
(a) explain and write equations for reactions of Group 17 ions with aqueous silver ions followed by aqueous ammonia;

(b) explain and write equations for reactions of Group 17 ions with concentrated sulphuric acid.

12.4 Industrial applications of halogens and their compounds

Candidates should be able to:
(a) describe the industrial uses of the halogens and their compounds as antiseptic, bleaching agent and in black-and-white photography;

(b) explain the use of chlorine in water treatment.

 

 

 

 

 

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