Oxidation State of Group 17 Elements

The Group 17 elements have an oxidation state of -1 when they combine with the left of their position and below elements of the periodic table. The elements of Group 17 of the periodic table are known as Halogens. Halogens are reactive nonmetals and include fluorine, chlorine, bromine, and iodine. The oxidation state of oxygen is usually -2 except in compounds with fluorine, oxygen has a positive oxidation number. All the elements of Group 17 form compound in odd oxidation states (-1, +1, +3, +5, +7) but down the group importance of the higher oxidation states generally decreases. Group 17 elements only required one additional electron to form a full octet. This characteristic makes them more reactive than the other non-metal groups.

What are Halogens?

The Group 17 elements of the periodic table are known as Halogen, in greek: Halo means salt and genes mean producing, so collectively halogens means salt producing. They are highly reactive nonmetals. Fluorine, chlorine, bromine, iodine, and astatine are the elements. Halogens react with metals to form compounds called salt. The halogen elements have seven valence electrons, that's why they are located on the left of the noble gases on the periodic table. Halogens have seven electrons in their outermost shell (ns2np5) and one electron is short from the configuration of the nearest noble gas.

Oxidation State

1. All elements of the halogen family exhibit -1 oxidation state.

2. Elements such as chlorine, bromine, and iodine also show +1, +3, +5, and +7 state.

3. When chlorine, bromine, and iodine, halogens in combination with small and highly electronegative atoms of fluorine and oxygen, the higher oxidation state is realized.

4. The oxoacids and oxides of bromine and chlorine have +6 and +4 states. Fluorine atoms can not expand its octet, because there are no valence shell d orbitals in fluorine.

5. Fluorine is the most electronegative element and exhibits only -1 oxidation state.

Physical Properties

  1. Physical state: Fluorine and chlorine are gases on the other hand bromine is a liquid and iodine is a solid.

  2. Colour: Group 17 elements have a variety of colours. For example, iodine is dark violet in colour and Fluorine is pale yellow in colour.

  3. Solubility: Chlorine and Fluorine are soluble in the water on the other hand Iodine and Bromine are less soluble in water.

Chemical Properties

1. Being highly reactive halogens react with metals and non-metals in order to form halides. As we move down the group reactivity of halogens decreases. Halogens have strong oxidizing properties among the halogen element, F2 is the strongest oxidizing halogen, it easily oxidizes the other halide ions present in the solid phase, or in the solution. Generally, halogen oxidizes the halide ions which are of higher atomic number. For Example: 

F2 + 2X- → 2F- + X2 ( where, X= Cl, Br or I)

2. With the help of reaction of halogens with water, the relative oxidizing nature can be illustrated. Where chlorine and bromine react with water and form hydrohalic and hypohalous acid.  In a non-spontaneous way, iodine reacts with water. With water in the acidic medium  I- can be oxidized. For example:

4I- (aq) + 4H+ (aq) + O2 (g) → 2I2 (s) + 2H2O (I)

1. General characteristics of Group 17 elements

Characteristics of Halogen Family

Symbol and name

Atomic Number

Electron Arrangement

Melting point 

Boiling point




2, 7

-220oC, 53K

-188oC, 85K




2, 8, 7

-101oC, 172K

-34oC, 235K




2, 8, 18, 7

-7oC, 256K

59oC, 332K




2, 8, 18, 18, 7

114oC, 387K

185oC, 458K




2, 8, 18, 32, 18, 7

302oC, 575K

337oC, 610K

2. Electronic Configuration

The halogen family members have seven valence electrons, which is halogens have seven electrons in their outermost orbit. From the nearest noble gas configuration halogens have one electron short. The configuration of the halogen family is given as ns2np5.

Atomic Number


Electronic Configuration



  2, 7



  2, 8, 7



  2, 8, 18, 7



  2, 8, 18, 18, 7



  2, 8, 18, 32, 18, 7

3. Electronegativity of Halogen Family

  1. Fluorine: 4.0

  2. Chlorine: 3.0

  3. Bromine: 2.8

  4. Iodine: 2.5

  5. Astatine: 2.2

Fun Facts

The elements of group 17 include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) from the top to the bottom. Group 17 elements are called “halogens” because they give salts when they react with metals. Group 17 elements are very reactive nonmetal. The electronic configuration of the valence shells of these electrons is ns2np5. Thus, in the outermost shell of these elements, the number of electrons is 7. The element misses out on the octet configuration by one electron. The atomic and nuclear radii of these elements keep on increasing as we move down the group. Due to the addition of an extra energy level, this happens. Their atomic charge is quite powerful and can be attributed to this fact.

These elements have various colours. Fluorine and chlorine are soluble in water, bromine and iodine are less soluble in water. Fluorine and chlorine are gases, on the other hand, bromine is liquid and iodine is solid.

FAQ (Frequently Asked Questions)

1. Mention some uses of Group 17 elements?

The uses of Group 17 elements:

  1. An important ingredient in toothpaste is Fluorine compounds. Because Fluorine compounds take care of teeth rotting by reacting with the enamel of the teeth.

  2. Majorly chlorine is being used as a bleach and also used in the metallurgy of elements like platinum and gold.

  3. Iodine is generally used as an antiseptic because it kills the germs on the skin.

2. Why are Group 17 elements are Dangerous?

All the Group 17 elements including fluorine, chlorine, bromine, iodine, and astatine are highly reactive nonmetals and are highly electronegative due to their highly effective nuclear charge. Halogens can gain an electron through reaction with other elements due to their high reactivity. To biological organisms in sufficient quantities, halogens can be harmful or lethal.