Alkali metals

Alkali metals are the group of elements in the first column of the periodic table, which includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Hydrogen also occupies the same column, but its properties differ from those of the metals, so it is generally not classified with this group.

The characteristic feature of this group is that each atom has a single electron in its outermost shell. This electron is easily released, making these substances highly reactive with other materials, particularly water and air. When they release the electron, they form a positively charged ion (M+).

Physical properties

These metals are soft—some can be cut with a knife—and have low melting points and low luster compared to other metals. Moving down the group, the melting point decreases: lithium has the highest, while cesium can melt at a temperature close to room temperature. All are excellent conductors of electricity and heat, and their surfaces are silvery-white when freshly cut.

Chemical reactivity

When placed in water, they produce hydroxide (such as NaOH) and hydrogen gas, releasing heat. The reaction becomes more vigorous as one moves down the group: lithium reacts gradually, sodium and potassium react rapidly, while rubidium and cesium react extremely vigorously. For this reason, these metals are not found in nature in pure form, but rather as salts and minerals in combination with other elements—for example, sodium chloride (table salt) and potassium compounds essential to plants.

Alkali metals are typically stored in mineral oil or under an inert gas to protect them from oxygen and moisture in the air. When burned, their flames produce different colors—sodium produces yellow, potassium produces violet—which is used to identify them in fireworks and street lamps.

Uses and significance

Lithium is widely used in rechargeable batteries for mobile phones and electric vehicles. Sodium and potassium play important roles in living organisms: they regulate water balance and the transmission of nerve signals. Cesium is used in atomic clocks that measure time precisely. Francium is extremely rare and decays rapidly (radioactive), so it has no commercial application.