Group 17 Chemistry

Group 17 Chemistry



– List out all the halogens in group 17?

F, Cl, Br, I, At

group 17 chemistry F Cl Br I At

– What is the properties of halogens?


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 colour shows from the elements group 17?

When move down the group the halogens become darker in colour.

F =  pale yellow , pale = pucat,
Cl =  pale green 
Br = red-brown
I = dark purple (at vapour state)
At = black

– What kind of molecules in halogens?

All the halogens exist as diatomic molecules, F2, Cl2, Br2, I2.

– What is the forces in halogens?

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.

– Why do the 1st ionization energy of halogens decrease down the group?

When moving down group, the number of electrons increases, atomic radius increases which decreases the attraction between nucleus and the valence electrons therefore, the strength of shielding increases. As a result, it is easier for valence shell electrons to ionize, and thus the ionization energy decreases down a group.

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.

What happen when going down group 17?

1. the atomic radius increases
2. the volatility decreases
3. the electron affinity decreases
4. the electronegativity decreases
5. the bond energy decreases
6. the oxidising power decreases
7. the reactivity towards hydrogen decreases.

group 17 trends halogens g7

1. the atomic radius increases

Down a group, the number of energy levels (n) increases, so there is a greater distance between the nucleus and the outermost orbital. This results in a larger atomic radius.

2. Down group 17, the volatility decreases (related to the density increases)

I2 < Br2 < Cl2 < F2

Because attractive forces increases in strength, packing of molecules increases and their density increases.

Volatility = the tendency of a substance to turn into a gas.

Low boiling point = high volatility (more volatile).

high boiling point = low volatility (less volatile)

Halogen Volatility

Polarity of molecules? Non-polar

Type of intermolecular bonds? Instantaneous dipole-induced dipole,

Cl2, lighter atoms, less electron, smaller dipoles, less energy to break intermolecular bonds, more volatile.

I2, heavier atoms, more electrons, bigger dipoles, more energy to break intermolecular bonds, less volatile.


– The volatility of the Group 17 elements, chlorine, bromine and iodine, decreases down the group. What is responsible for this?

A Bond length in the halogen molecule

B Bond strength in the halogen molecule

C Number of electrons in the halogen molecule

D Electronegativity of the halogen


3. the electron affinity decreases? 

Electron affinity refers to the amount of energy that is liberated whenever a molecule or a neutral atom tends to add an electron from the other elements.

A. F > Cl > Br > I (wrong)
B. Cl > F > Br > I (correct)

Cl (-349) > F (-328) > Br (-325) > I (____)

Small atomic has higher electron affinity. From Cl, Br to I, electron affinity decreases due to the increasing atomic radius.

F smaller than Cl but not F has higher electron affinity, why? It is because, fluorine atom is very small as compared to chlorine atom and due to its small size there are strong inner repulsion among valence electrons and so the outer electron does not feel the attraction from the nucleus. So electron affinity of fluorine is less than that of chlorine. 

The electrons in the outermost shell of a fluorine atom are closer together. Energy is required to keep the gained electron in the shell, causing fluorine to have a smaller electron affinity than chlorine

4. the electronegativity decreases

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. As when down group, the radius of each atom increases due to more shells. This means there is less attraction between the positive nucleus and the outer electrons as you go down the 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 atom is very small and 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

5. the bond energy decreases

A molecule with highest bond energy?

A. Fluorine

B. Chlorine

C. Bromine

D. Iodine

The order of bond dissociation energy is: Cl2 > Br2 > I2 > F2.

– Why bond energy of halogens decrease down the group?

On moving down the group of halogens, Chlorine will have the highest bond energy. Apart from the fluorine case, the bond energy (bond dissociation energy) decreases from chlorine to bromine and to iodine. The halogen atoms are getting bigger, and so the bonding electrons are further from the halogen nucleus, and experience less attraction towards it. The bond is therefore more easily broken.

Fluorine is exceptionally has lowest bond energy because:

1. it has small atomic size due to which the electrons are held in a compact volume,

2. consequently (akibatnya) there is strong repulsion among non bonded electrons.

3. interelectronic repulsions due to small sized F atom.

4. Hence (oleh itu), bond becomes weak though (walaupun) bond is short. Due to this reason bond dissociation energy of fluorine less than other halogens.

6. the oxidising power decreases (accept electron)

when down group, the atomic radius is increases, the ability of halogen atoms to recieve electron decreases. Fluorine is the strongest oxidizing agent because fluorine atoms are the smallest halogen atoms, and so accept electrons most easily. Down group 17, as the halogen atoms get larger, they accept electrons less easily, and the oxidizing power becomes weaker.

7. the reactivity towards hydrogen decreases.

The reactivities of the halogens decrease down the group ( F > Cl > Br > I > At ).

This is because the atomic radius increases in size with an increase of electronic energy levels. This lessens the attraction for valence electrons of other atoms, decreasing reactivity.

– Reactivity halogens towards Hydrogen is decreases.

reaction with hydrogen cl2 br2 i2

Because of the bond energy decreases,

HI is a stronger acid than HCl,

HI bond enthalpy lower than HCl,

HI longer bond than HCl,

HI small overlap than HCl,

HI less energy required to dissociates than HCl.

Reactivity halogens towards hydrogen

Reducing character is the ability of a substance to reduce something else. So it itself must get oxidized.

litmus paper test blue red base acid

– HIO3 weaker acid than HClO3

Cl more electronegative with small atomic radius, Cl atom in HClO3 pull away, less energy required to build the bond. Higher decreases dissociation, H2O+ increases.


– Acidity increases (acid strength)

(weaker acid) HClO < HClO2 < HClO3 < HClO4 (stronger acid)


– For the hydrogen halides, HX:

the boiling point increases in the order HCI < HBr <HI .

thermal stability decreases in the order HCI > HBr > HI

the acid strength increases in the order HCI < HBr <HI


– The solubility of the silver halides, AgX in ammonia decreases in the order: AgCl > AgBr > Agl

The solubility of the silver halides AgX in ammonia decreases in the order AgCl AgBr Agl


– Concentration of H2SO4, sulphuric acid react with:

chloride –> HCl

bromide –> HBr and Br2

iodide –> HI and I2

– Chlorine, Cl2 react with:

cold dilute sodium hydroxide, NaOH –> chloride, Cl- and Chlorate (i)

hot concentrated sodium hydroxide, NaOH –> chloride, Cl- and Chlorate (v)

Add Comment