Periodic Trends in Group 17 Elements Atomic Size Electronegativity and Reactivity
Group 17 elements of the periodic table comprises Halogens. They come under the p-block elements of the modern periodic table. There are five Halogens and in order of valency in the periodic table they are as follows: Chlorine, Fluorine, Iodine, Bromine and Astatine. The word “Halogen” is a Greek word which means salt producer due to the properties of elements like Bromine, Chlorine and Iodine. Halogens exhibit high electronegativity and the anions formed become the anionic part of the salts which are widely found in seawater. Electronegativity is defined as the ability of an atom to accept an electron and form an octet. The last element of the group, Astatine, is radioactive in nature. In this article, students will learn about Halogens and their properties.
What are Halogens?
Halogens are highly reactive nonmetals belonging to the 17th group of the periodic table. They have seven electrons in their outermost shell with the electronic configuration ns2np5. They are highly electronegative in nature as they are only one electron short of the nearest noble gas configuration. Out of the five Halogens, Astatine is the only radioactive element. The Physical and Chemical properties of Halogens are greatly similar which is not observed in other groups.
Properties of Halogens
Physical Properties
Halogens exhibit smooth transitions in their Physical state. Chlorine and fluorine are glasses naturally, bromine is liquid in its natural state and iodine is solid in nature.
With change in atomic number, the melting and the boiling points of the elements change.
Halogens are usually coloured due to the absorption of radiation in their visible regions. Fluorine exhibits yellow color, bromine shows red color, Chlorine is greenish-yellow in color and iodine is violet.
Chlorine and fluorine dissolve in water completely, iodine and bromine are partially soluble in water but completely soluble in organic solvents such as chloroform disulphide.
Chemical Properties
Halogens show a -1 oxidation state, however, bromine, Chlorine and fluorine can also exhibit +1, +3, +5 and +7 oxidation states as well. The higher oxidation states are exhibited only when Halogens combine with highly electronegative atoms like oxygen and fluorine. They are usually highly reactive and can react with metals and nonmetals alike, thus, forming halides. They can readily accept an electron to complete electronic configuration and form an octet. Out of all the Halogens, fluorine is the strongest Oxidizing agent.
Trends Among Halogens
Reactivity of Halogens decreases down the group.
Halogens have a small atomic size.
They have a high nuclear charge.
Group 17 Trends Properties
The modern periodic table's group 17 consists of the following elements.
Chlorine
Fluorine
Iodine
Bromine
Astatine
These elements are called halogens. Halogen is a Greek word, which means a salt producer. These elements are known as salt producers due to the properties exhibited by bromine, chlorine, and iodine. They are highly electronegative in nature and form anions, which constitute the anionic part of salts found in the seawater. Astatine is the last element of the group and is radioactive in nature. These elements belong to the p block of the modern periodic table. The halogen family constitutes the most homogenous group after the alkali group in the modern periodic table.
Did You know?
Why is the electron affinity of chlorine more than that of fluorine?
Answer: This is due to the compact structure of fluorine. Chlorine has a larger atomic size hence it can accommodate more electrons, whereas the electrons in fluorine are closely-spaced. So, the crowded electrons in fluorine screen its effective nuclear charge, and thus, it exhibits a lower electron affinity.
FAQs on Group 17 Trends and Properties of Halogens
1. What are Group 17 elements in the periodic table?
The Group 17 elements, also called halogens, are fluorine, chlorine, bromine, iodine, and astatine. These elements are located in Group 17 of the periodic table and have similar chemical properties because they all have seven valence electrons (ns2np5).
- Fluorine (F)
- Chlorine (Cl)
- Bromine (Br)
- Iodine (I)
- Astatine (At)
2. Why are Group 17 elements called halogens?
Group 17 elements are called halogens because they are "salt-formers" when they react with metals. The term halogen comes from Greek words meaning “salt-producing.”
- They react with metals to form ionic halides.
- Example: 2Na(s) + Cl2(g) → 2NaCl(s)
3. What is the general electronic configuration of Group 17 elements?
The general electronic configuration of Group 17 elements is ns2np5. This means they have seven electrons in their outermost shell.
- They need one more electron to complete an octet.
- This explains their high electron affinity and reactivity.
4. How does atomic size change down Group 17?
The atomic radius increases down Group 17 from fluorine to astatine. This trend occurs because additional electron shells are added as we move down the group.
- More energy levels increase shielding effect.
- Valence electrons are farther from the nucleus.
5. How does reactivity change down the halogen group?
The reactivity of halogens decreases down Group 17. Fluorine is the most reactive, while iodine and astatine are less reactive.
- Smaller atoms gain electrons more easily.
- Electronegativity decreases down the group.
6. What is the trend in electronegativity in Group 17?
The electronegativity decreases down Group 17 from fluorine to astatine. Fluorine is the most electronegative element in the periodic table.
- Increased atomic size reduces nuclear attraction for bonding electrons.
- Shielding effect increases down the group.
7. In what physical states do Group 17 elements exist at room temperature?
At room temperature, halogens exist in all three physical states: gases, liquid, and solid. Their physical state changes down the group due to increasing intermolecular forces.
- F2 and Cl2 are gases.
- Br2 is a liquid.
- I2 and At are solids.
8. Why do halogens form -1 ions?
Halogens form -1 ions (X-) because they gain one electron to complete their octet configuration. With seven valence electrons, gaining one electron gives them a stable noble gas configuration.
- Example: Cl + e- → Cl-
- This forms stable ionic compounds like NaCl.
9. What are displacement reactions in Group 17?
A displacement reaction in Group 17 occurs when a more reactive halogen displaces a less reactive halogen from its salt solution. Reactivity decreases down the group.
- Chlorine displaces bromine: Cl2(aq) + 2KBr(aq) → 2KCl(aq) + Br2(aq)
- Bromine cannot displace chlorine from KCl.
10. How do the oxidizing properties change down Group 17?
The oxidizing power decreases down Group 17 because the ability to gain electrons decreases. Fluorine is the strongest oxidizing agent among the halogens.
- Strong oxidizing agents readily gain electrons.
- Example: F2(g) + 2e- → 2F-
