Group 1 elements, commonly referred to as alkali metals, exhibit a vigorous reaction with water, resulting in the production of hydrogen gas and alkali metal hydroxides.

The alkali metals include lithium ($\text{Li}$), sodium ($\text{Na}$), potassium ($\text{K}$), rubidium ($\text{Rb}$), cesium ($\text{Cs}$), and francium ($\text{Fr}$). These metals are characterized by their high reactivity, particularly with water. When an alkali metal interacts with water, a chemical reaction takes place, yielding hydrogen gas and an alkali metal hydroxide. This reaction is exothermic, meaning it releases heat. In some cases, the heat generated during the reaction can be sufficient to ignite the hydrogen gas, potentially leading to a fiery explosion.

The general equation for this reaction can be expressed as:

In this equation, $M$ represents an alkali metal, while the symbols $(s)$, $(l)$, $(aq)$, and $(g)$ indicate the physical states of the reactants and products: solid, liquid, aqueous, and gas, respectively.

The reactivity of alkali metals increases as one moves down the group. This trend is attributed to the outermost electron, which is involved in the reaction being situated further from the nucleus. As a result, this electron is held less tightly, making it easier to be donated to a water molecule, thereby facilitating the reaction. For instance, lithium reacts slowly with water, sodium reacts vigorously, and potassium can react explosively.

In laboratory settings, it is crucial to handle these reactions with caution due to the production of hydrogen gas and the exothermic nature of the reactions. Typically, alkali metals are stored under oil to prevent accidental contact with water, which could trigger unwanted reactions.

In conclusion, Group 1 elements react with water to form hydrogen gas and alkali metal hydroxides. This reaction is exothermic and displays increasing reactivity as you proceed down the group.