Group 1 (alkali metals) – lithium, sodium and potassium

What are Group 1 elements?

Lithium, sodium, potassium, rubidium, cesium; soft metals that form 1⁺ ions and react similarly.

Why are lithium, sodium, and potassium called a family of elements?

They have similar chemical properties, react similarly with water and air, and have one electron in their outer shell.

Describe the reaction of lithium with water

Lithium floats, fizzes gently, forms lithium hydroxide and hydrogen gas.

Describe the reaction of sodium with water

Sodium melts into a ball, fizzes rapidly, forms sodium hydroxide and hydrogen gas.

Describe the reaction of potassium with water

Potassium ignites with a lilac flame, fizzes violently, forms potassium hydroxide and hydrogen gas.

What trend is observed in the reactions of Group 1 elements with water?

Reactivity increases down the group; reactions become faster and more vigorous.

Explain why reactivity increases down Group 1

Outer electron is further from nucleus, weaker attraction, easier to lose, so reactivity increases.

How do Group 1 metals react with air?

Lithium forms a dull oxide, sodium forms oxide and peroxides, potassium forms oxide, peroxide, and superoxide; reactivity increases down the group.

Why does lithium react slower with water than sodium or potassium?

Lithium’s outer electron is closer to the nucleus, so it is held more strongly and lost less easily.

Predict the reaction of rubidium with water

Rubidium reacts explosively with water, forming rubidium hydroxide and hydrogen gas.

Predict the reaction of cesium with water

Cesium reacts extremely violently with water, forming cesium hydroxide and hydrogen gas.

Explain the trend in melting points of Group 1 metals

Melting points decrease down the group due to weaker metallic bonding as atoms get larger.

Explain the trend in density of Group 1 metals

Density generally increases down the group as atomic mass increases faster than volume.

Explain why Group 1 metals form 1⁺ ions

They each have one electron in the outer shell which is easily lost to achieve a full inner shell.

How can the reaction of an alkali metal with water be used to identify it?

Observe reaction rate, hydrogen gas evolution, flame color; potassium gives lilac flame, sodium yellow, lithium no flame.

Explain the trend in reactivity in terms of electronic configuration

Down the group, outer electron is further from nucleus, less attracted, lost more easily, increasing reactivity.

How does reaction with oxygen provide evidence for reactivity trends?

Lithium forms Li₂O, sodium forms Na₂O₂, potassium forms KO₂; larger metals form more complex oxides, showing increasing reactivity.

How does reaction with water provide evidence for reactivity trends?

Lithium reacts slowly, sodium moderately, potassium vigorously; shows reactivity increases down the group.

Predict properties of other alkali metals

Other alkali metals (Rb, Cs) will be very soft, low melting points, highly reactive, form 1⁺ ions, react violently with water.

Explain why these trends support classification as a family

All have one outer electron, similar chemical reactions, gradual trends in reactivity and physical properties, consistent with Group 1.

Describe practical safety precautions when reacting Group 1 metals with water

Use small pieces, safety goggles, gloves, perform behind safety screen, use trough of water to contain reaction