Using the periodic table, identify the lightest member of each of the following groups: (a) noble gases (b) alkaline earth metals (c) alkali metals (d) chalcogens

Noble gases are a group of chemical elements with similar properties found in group 18 of the periodic table. Known for their lack of reactivity, these gases are colorless, odorless, and tasteless. The lack of reactivity stems from their full valence electron shell, making it unnecessary for them to gain or lose electrons to achieve a stable configuration.
Noble gases include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). Helium, with an atomic number of 2, is not only the lightest noble gas but also the second lightest element in the entire periodic table. It is primarily used in applications requiring low temperatures like MRI machines, and as a lifting gas in balloons and airships due to its lighter-than-air characteristics.
Despite their non-reactivity, some noble gases do form compounds under specific extreme conditions. The first noble gas compound discovered was xenon hexafluoroplatinate in 1962.

Alkaline earth metals are found in group 2 of the periodic table, characterized by their shiny, silver-white metallic surface and their ability to conduct heat and electricity. These elements are called 'earth metals' because of their presence in various minerals within the Earth's crust.

• Beryllium (Be) - Atomic number 4
• Magnesium (Mg) - Atomic number 12
• Calcium (Ca) - Atomic number 20
• Strontium (Sr) - Atomic number 38
• Barium (Ba) - Atomic number 56
• Radium (Ra) - Atomic number 88

Beryllium, the lightest member with an atomic number of 4, is extensively used in aerospace applications for its high strength-to-weight ratio and thermal stability. Alkaline earth metals have two valence electrons, which they readily lose to form divalent cations, contributing to their high reactivity. These elements are also essential in biological processes; for instance, magnesium and calcium are vital for living organisms.

Alkali metals, occupying group 1 of the periodic table, are known for being soft, highly reactive, especially with water, and having a single electron in their outermost shell.
Following their increasing atomic number, they include:

• Lithium (Li) - Atomic number 3
• Sodium (Na) - Atomic number 11
• Potassium (K) - Atomic number 19
• Rubidium (Rb) - Atomic number 37
• Caesium (Cs) - Atomic number 55
• Francium (Fr) - Atomic number 87

Lithium, the lightest, with an atomic number of 3, is extensively used in rechargeable batteries. The tendency of alkali metals to lose their single valence electron makes them excellent conductors of electricity. They typically form ionic bonds, creating strong compounds widely utilized in various industries, from electronics to pharmaceuticals.

Chalcogens are the elements found in group 16, which includes oxygen, sulfur, selenium, tellurium, and polonium. They exhibit diverse physical and chemical properties but share the common characteristic of needing two electrons to complete their valence shell.

• Oxygen (O) - Atomic number 8
• Sulfur (S) - Atomic number 16
• Selenium (Se) - Atomic number 34
• Tellurium (Te) - Atomic number 52
• Polonium (Po) - Atomic number 84

Oxygen, the lightest chalcogen with atomic number 8, is vital for the process of respiration and is the most abundant element in the Earth's crust. Chalcogens can form various compounds, including oxides, sulfides, and selenides, many of which are crucial for industrial applications such as electronics, glassmaking, and as semiconductors.