Group 17 (Halogens) and Group 18 (Noble gases) - SS3 Chemistry Lesson Note
Group 17 and Group 18 are two neighbouring groups in the p-block of the periodic table, consisting of elements known as the Halogens and the Noble gases, respectively. These groups exhibit distinct properties and behaviours, making them significant in various chemical and industrial applications. Let's explore the characteristics of Group 17 (Halogens) and Group 18 (Noble gases) in detail:
Group 17 - Halogens:
1. Elements: Halogens consist of five elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Fluorine and chlorine are gases at room temperature, bromine is a liquid and iodine and astatine are solids.
2. Electron Configuration: Group 17 elements have seven valence electrons in their outermost electron shell (ns2 np5). The halogens have a strong tendency to gain one electron to achieve a stable noble gas electron configuration.
3. Reactivity: Halogens are highly reactive nonmetals, especially alkali metals and alkaline earth metals. They readily form halide ions (F-, Cl-, Br-, I-) by gaining an electron. Their reactivity decreases as you move down the group. Fluorine is the most reactive halogen, while iodine is less reactive.
4. Diatomic Molecules: Halogens exist as diatomic molecules in their elemental forms (e.g., F2, Cl2, Br2, I2). The diatomic nature of halogens is due to the sharing of electrons through a single covalent bond between two atoms of the same element.
5. Halides and Acids: Halogens form halide salts with metals and hydrogen halides (e.g., hydrofluoric acid, hydrochloric acid). Halides are essential in various chemical processes and industrial applications.
6. Biological Importance: Halogens play a role in biological systems, such as the presence of iodine in thyroid hormones (thyroxine and triiodothyronine).
Group 18 - Noble Gases:
1. Elements: The Noble gases consist of six elements: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All noble gases are gases at room temperature and are chemically inert.
2. Electron Configuration: Noble gases have complete electron shells with full valence electron configurations (ns2 np6). This stable electron configuration makes noble gases chemically unreactive.
3. Inert Nature: Noble gases are highly unreactive and do not readily form chemical compounds under normal conditions. Their lack of reactivity is due to the stability of their electron configuration.
4. Uses:
● Helium is used in various applications, including filling balloons, cryogenics, and as a coolant in certain scientific equipment.
● Neon is famous for its use in neon signs due to its bright and colourful emission spectrum when an electrical current is applied.
● Argon is used in various industries as an inert shielding gas.
● Xenon has applications in lighting, anaesthesia, and high-pressure arc lamps.
5. Radioactivity: Radon is a radioactive noble gas and is considered a health hazard when present in indoor air due to its potential link to lung cancer.
Both Group 17 (Halogens) and Group 18 (Noble gases) have unique properties that make them valuable in different applications. The halogens' reactivity and ability to form compounds find applications in various chemical and industrial processes, while the noble gases' inert nature and unique properties make them useful in lighting, cryogenics, and other specialised fields.