Group I Elements: Properties and Predictions

This document provides detailed notes on the properties of Group I elements (alkali metals) and how to predict the properties of other elements within the group.

Properties of Group I Elements

Group I elements (Li, Na, K, Rb, Cs, Fr) exhibit characteristic properties due to their electronic configuration. They all have one electron in their outermost shell, which is readily lost to form a +1 ion.

Reactivity

Reactivity increases as you go down Group I. This is because the outermost electron is further from the nucleus and is more easily removed. The larger atomic size also means the effective nuclear charge is lower, making it easier to lose the electron.

Key Points:

• Lithium (Li) is relatively unreactive.
• Sodium (Na) is reactive.
• Potassium (K) is more reactive than Sodium.
• Rubidium (Rb) is even more reactive than Potassium.
• Cesium (Cs) is the most reactive alkali metal.

Physical Properties

Physical properties also change down the group:

• Melting Point & Boiling Point: Melting and boiling points decrease down the group. This is due to the weaker metallic bonding. More electrons mean weaker attraction between the delocalised electrons and the metal ions.
• Density: Density increases down the group. Larger atomic size and more mass contribute to this.
• Colour: Alkali metals are silvery-white and shiny.
• Hardness: Alkali metals are soft and can be cut with a knife.

Chemical Properties

Chemical properties are the most significant aspect of Group I elements:

• Reaction with Water: Alkali metals react vigorously with water. The reactivity increases down the group. The reaction produces hydrogen gas and a metal hydroxide. The heat produced can be significant, and for the more reactive metals, the reaction can be explosive.
• Reaction with Air: Alkali metals react with oxygen in the air to form oxides. The reactivity increases down the group.
• Reaction with Halogens: Alkali metals react readily with halogens (Group 17) to form ionic compounds (metal halides). The reactivity increases down the group.
• Electrolysis: Alkali metals are easily reduced to their elemental state by electrolysis.

Predicting Properties of Other Group I Elements

Based on the trends observed in Group I, you can predict the properties of other elements within the group:

Reactivity Prediction

To predict the reactivity of an unknown Group I element, consider its position in the group. Elements further down the group are generally more reactive.

Example: If you have an element located between Potassium and Rubidium, it will be more reactive than Potassium but less reactive than Rubidium.

Physical Property Prediction

Similarly, physical properties can be predicted based on the element's position in the group. Melting point, boiling point, density, and hardness will generally follow the same trends as observed in the known elements.

Chemical Property Prediction

The chemical properties are the easiest to predict. Consider the reactivity with water, air, and halogens. An element further down the group will be more reactive in these reactions.

Note: The reactivity with water, air, and halogens increases as you move down the group. Melting point and boiling point generally decrease as you move down the group.

Safety Precautions

Alkali metals react vigorously with water and other substances. Therefore, appropriate safety precautions must be taken when handling them:

• Always wear safety goggles.
• Handle alkali metals in a dry environment.
• Avoid contact with water.
• Dispose of alkali metals properly.