Final answer:
The highly reactive elements on the far left of the periodic table are called alkali metals, which include elements like lithium and sodium. These metals react with water to form alkaline solutions and are characterized by their tendency to lose a single valence electron.
Step-by-step explanation:
The elements on the far left of the periodic chart that are very reactive are known as alkali metals. These include lithium, sodium, potassium, rubidium, cesium, and francium which constitute group 1 of the periodic table. The name 'alkali metal' comes from the fact that these metals react with water to form very basic (alkaline) solutions. Alkali metals are known for their high reactivity; they readily lose their single valence electron to form cations with a charge of +1, and as a result, they engage in reactions readily. Notably, the halogens (group 17) are the most reactive nonmetals, while noble gases (group 18) are the least reactive nonmetals, known as inert gases.