Provide the following:
a. the atomic number and symbol of the lightest alkali metal
b. the atomic number and symbol of the heaviest noble gas

Alkali metals are a group of elements found in Group 1 of the periodic table, characterized by their single valence electron, which makes them highly reactive. The lightest alkali metal is lithium, with an atomic number of 3 and the symbol 'Li'. These metals are known for their low density and are typically found in nature only in compound form.

Noble gases are located in Group 18 of the periodic table and are known for their lack of reactivity due to having a full valence shell of electrons. The heaviest noble gas is radon, which has an atomic number of 86 and the symbol 'Rn'. These gases are colorless, odorless, and exist in a gaseous state at room temperature.

The atomic number of an element is the number of protons found in the nucleus of an atom, which determines the element's identity and its position in the periodic table. Each element is also represented by a unique chemical symbol, typically one or two letters derived from its name, such as 'Li' for lithium and 'Rn' for radon. Understanding these concepts is essential for identifying elements and their properties.