Group 1 (I) Alkali Metals: Properties and Trends

Group 1 contains lithium (Li), sodium (Na), and potassium (K). They are called alkali metals because they form alkaline (basic) solutions when they react with water.

Key Physical Properties

• Soft metals: can be cut with a knife; freshly cut surfaces are shiny and silver but quickly turn dull (react with oxygen).
• Low density: Li, Na and K float on water. Density generally increases down the group.
• Melting point: decreases down the group (lithium has the highest melting point of the three).
• Electrical conductivity: good conductors (they are metals).

Electronic Structure and Ions

Each atom has one electron in its outer shell: Li: $2,1$, Na: $2,8,1$, K: $2,8,8,1$. They lose this electron to form $M^+$ ions (charge +1) and make ionic compounds such as NaCl.

Reactivity Trend (Why they get more reactive)

Reactivity increases down the group. The outer electron is farther from the nucleus and held less tightly, so it is lost more easily. Think of a magnet holding a paperclip: the farther away it is, the weaker the pull.

Reactions to Know

• With water: fizzing (hydrogen gas) and an alkaline solution (metal hydroxide). The reaction gets more vigorous from Li → Na → K. Potassium may ignite with a lilac flame.

General equation:

$$2M(s) + 2H_2O(l) \rightarrow 2MOH(aq) + H_2(g)$$

• With oxygen: form oxides; these metals are stored under oil to stop reactions with air and water.

Common Misconceptions

• “All metals are hard and heavy.” Group 1 metals are soft and low density (Li, Na, K float).
• “Reactivity decreases down the group.” It increases down Group 1.
• “Sodium is safe in water.” It produces hydrogen gas and a strong alkali; it must be handled with care.