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Why do alkali metals form ionic compounds with nonmetals?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkali metal Modern version of the periodic table of the elements (printable).

Alkali metals form ionic compounds with nonmetals primarily because of their electronic structure and low ionization energy.12

Each alkali metal atom possesses a single, weakly bound valence electron in its outermost shell. Because these metals have very low electronegativity, they readily lose this electron to achieve a stable, noble-gas electron configuration.213

When an alkali metal reacts with a nonmetal—which typically has a high electronegativity and a strong tendency to gain electrons—the metal atom transfers its valence electron to the nonmetal atom. This process creates a positively charged cation and a negatively charged anion. The resulting ionic compound is held together by the strong electrostatic attraction between these oppositely charged ions, forming hard crystals with high melting points.12