Alkali metals are a group of elements in the periodic table that includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). These metals are highly reactive and form various compounds with different elements.

Compounds formed by alkali metals:

1. Amides (MNH2): All alkali metals form amides by reacting with nitrogen gas. The general formula of amides is MNH2, where M represents an alkali metal. For example, lithium amide (LiNH2), sodium amide (NaNH2), and potassium amide (KNH2) are some commonly known amides.

2. Ionic salts like hydrides (MH): Alkali metals react with hydrogen gas to form ionic hydride salts. The formula of hydrides is MH, where M represents an alkali metal. For example, lithium hydride (LiH), sodium hydride (NaH), and potassium hydride (KH) are some commonly known hydrides.

3. Basic oxides: Alkali metals react with oxygen gas to form basic oxides. The formula of basic oxides is MO, where M represents an alkali metal. For example, lithium oxide (Li2O), sodium oxide (Na2O), and potassium oxide (K2O) are some commonly known basic oxides.

Compounds that alkali metals do not form:

Superoxide like KO2: Alkali metals do not form superoxide compounds like KO2. Superoxides are formed when alkali metals react with oxygen gas in the presence of excess oxygen. For example, potassium superoxide (KO2) is a superoxide compound that is formed by reacting potassium metal with oxygen gas in the presence of excess oxygen. However, other alkali metals do not form superoxides.

Conclusion:

In conclusion, all alkali metals form amides, hydrides, and basic oxides, but they do not form superoxide compounds like KO2.