Final answer:
Group IA elements, or alkali metals, are called reactive metals due to their single valence electron, which can be lost easily, leading to high reactivity. Group VIIA elements, known as halogens, are reactive nonmetals as they readily gain an electron to complete their valence shell, forming stable compounds, particularly halide salts.
Step-by-step explanation:
Elements in group IA (1), also known as alkali metals, are highly reactive metals because they have only one electron in their outer shell, which they can easily lose to form a stable electronic configuration. This single valence electron can be lost with minimal energy, making alkali metals highly reactive when they come into contact with other substances, such as water or halogens.
On the other hand, elements in group VIIA (17), also referred to as halogens, are reactive nonmetals. They have seven valence electrons, just one electron short of a full shell, making them very eager to gain an electron to achieve a stable electron configuration. Because of this, halogens form compounds readily, particularly with alkali metals and alkaline earth metals, to create halide salts.
The reactivity of these elements is influenced by their position in the periodic table, which is based on Mendeleev's principle of organizing elements by their chemical properties. Alkali metals in group IA and halogens in group VIIA are arranged such that their similar reactivity patterns define their respective groups as reactive metals and reactive nonmetals.