Group 17 elements, The Noble gas elements

Halogen Family:

Halogen family consists of seven elements which are Fluorine, Chlorine, Bromine, Iodine, and astatine. Astatine is radioactive.

All the elements of group 17 elements (Except At) react with metals to give salts so they are called halogen(Sea Salt forming elements).

In each family, we generally study The preparation of elements, its physical properties, Chemical properties, and uses. So let’s discuss one by one.

Chemistry is vast and memorizing everything is not so easy. So we will use some tricks and tips to learn things easily.

Physical properties:

To learn various physical properties remember a small trick  ”All India English Medium School”. Here the first capital letters represent A=Atomic Radius, I=Ionisation energy, E=Electron affinity and Electronegativity, M=melting and boiling Point, S= State. So let’s start one by one.

Atomic Radius;

The halogens have the smallest atomic radii in their respective periods due to the maximum effective nuclear charge. (Generally, Atomic radius Increases down The group and decreases along the period). So both atomic and ionic radii will increase down the group as the addition of a new energy shell. So the trend is F<Cl<Br<I.

Ionisation Energy;

Down the group, Ionisation energy Decreases because down the group size increases and effective nuclear charge decreases so the electron experience less force of attraction.

So I.E trend is F>Cl>Br>I

Electron affinity:

Down the group, EA generally  Decreases. EA of Cl is more than F.

The reason; Due to the small size of Fluorine the electron density around the nucleus increases so the incoming electron suffers more repulsion. But in chlorine, the electron density decreases due to large size.

EA trend Cl>F>Br>I

Halogens have extremely high Electron gain enthalpy (Electron affinity and electron gain enthalpy is the same) in their respective periods.


Down the group Electronegativity Decreases

EN trend F>Cl>Br>I

Melting Point and Boiling Point;

Melting and boiling points of these elements increase regularly from Fluorine to Iodine.

Oxidation State:

The general electronic configuration of halogen family is ns2 np5

So there is only 7 valence shell electron. so they will try to gain an electron to complete their octet. So the State is -1.

Higher elements have vacant d subshell so they can show +1,+3, +5 and +7 oxidation states.

But Fluorine only Shows -1 due to small size and unavailability of d-orbital. Cl, Br, & I show  +1, +3, +5, +7 oxidation states because of the presence of empty d-orbital in their valence shells. The positive oxidation states are seen in interhalogens, oxoacids, and oxides.

Oxidation states of Halogens
      F  Only -1
     Cl -1 to +6
     Br -1 to +6
      I -1 to +6

Physical state: The group 17 elements exist in the various physical state

All these are diatomic in nature. Intermolecular forces in halogens are weak
and increase down the group. Thus F2, Cl2 are gases, Br2
volatile liquid and I2 volatile solid
Color:  These elements display diverse colors
F→ Pale yellow color
Cl → Greenish yellow color
Br → Reddish-brown color
I → Dark violet color
Solubility:  F, Cl is soluble in water
Br, I, are sparingly dissolvable in the water yet totally dissolvable in organic solvents

Metallic Nature:  The metallic nature increases as we move down the group.
Due to high ionization enthalpy values all these elements are non-metallic in nature.
Density: The densities increases moving from F to I.

Chemical Properties:

In chemical properties, we will study the order of Reactivity and reactivity towards other elements and compounds. Generally, an element combines with  H2, Oxygen, Nitrogen, Halogen X2, and Metals. So we will apply this general rule in every family.


All the halogens are non-metallic in nature. they have high electron gain enthalpy and high electronegativity and have a relatively smaller size than the respective period members. So they are highly reactive. And the reactivity decreases down the group.

Reactivity of F>Cl>Br>I

Oxidizing Nature

Halogens show the oxidising property as they easily accept an electron and undergo reduction itself. So they are great oxidizing agents. So they show oxidation and reduction reaction.

Remember: Xact as Oxidising agent and X–  act as Reducing agent

Fluorine is the best oxidizing agent and can oxidize all other halide particles to halogen in a solution. As we move down the group from F to I, oxidizing power decreases. Hence Chlorine can oxidize bromide particles to bromine and iodide particles to iodine. Similarly, bromine can oxidize iodide particles to iodine.

Cl2 + 2Br¯ → Br2 + 2Cl¯

Cl2 + 2I¯ → I2 + 2Cl¯

Br+ 2 I¯ → I2 + 2Br¯

Reaction with Hydrogen;

All halogens reacts with hydrogen to form halogen halides which are acidic in nature.

The acidic strength Increases down the group.

As mentioned earlier the fluorine has high reactivity so fluorine reacts vigorously with H2 even in dark.

H2 + F2  2HF

Hope you remember the Story that Toka Swu sir told.Clrequires sunshine while bromine reacts with hydrogen just on heating. Iodine reacts with hydrogen on heating in the presence of a catalyst.

In dark

H2 + Cl2  No reaction

In sunlight

H2 + Cl2  2HCl

Reaction with Oxygen


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