1.2.5 Group 7

In this lesson, we will explore the unique properties of alkali metals, their reactions with oxygen, chlorine, and water, and the trend of increasing reactivity as you move down the group.

Alkali Metals - Group 1

The elements in Group 1 of the periodic table are known as the alkali metals. This group includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkali metals share similar properties due to the presence of a single electron in their outer shell.

Properties and Outer Shell Electrons

The properties of elements in Group 1 depend on the outer shell of electrons in their atoms. The outer shell, also known as the valence shell, is the outermost energy level where electrons are located. It plays a crucial role in determining the chemical behaviour and physical properties of an element.

Single Electron in Outer Shell

Alkali metals have one valence electron in their outermost energy level. This lone electron is loosely bound to the nucleusA membrane-bound organelle in eukaryotic cells that contains DNA. and is easily lost during chemical reactions. The presence of a single valence electron contributes to the characteristic properties and reactivity of alkali metals.

Reactivity of Alkali Metals

Alkali metals are highly reactive due to the ease with which they can lose their single valence electron to achieve a stable electron configuration. As you move down Group 1, the reactivity of the alkali metals increases.

Reactions with Oxygen

Alkali metals react vigorously with oxygen to form metal oxides. The reaction involves the alkali metal atoms combining with oxygen atoms to produce metal oxide compounds. For example:

• Lithium (Li) reacts with oxygen (O₂) to form lithium oxide (Li₂O).
• Sodium (Na) reacts with oxygen (O₂) to form sodium oxide (Na₂O).
• Potassium (K) reacts with oxygen (O₂) to form potassium oxide (K₂O).

Reactions with Chlorine

Alkali metals react readily with chlorine to form metal chloride compounds. The reaction involves the alkali metal atoms transferring their valence electron to the chlorine atoms. For example:

• Lithium (Li) reacts with chlorine (Cl₂) to form lithium chloride (LiCl).
• Sodium (Na) reacts with chlorine (Cl₂) to form sodium chloride (NaCl).
• Potassium (K) reacts with chlorine (Cl₂) to form potassium chloride (KCl).

Reactions with Water

Alkali metals react vigorously with water, producing hydrogen gas and metal hydroxide compounds. The reaction involves the alkali metal atoms displacing hydrogen from water molecules. For example:

• Lithium (Li) reacts with water (H₂O) to form lithium hydroxide (LiOH) and hydrogen gas (H₂).
• Sodium (Na) reacts with water (H₂O) to form sodium hydroxide (NaOH) and hydrogen gas (H₂).
• Potassium (K) reacts with water (H₂O) to form potassium hydroxide (KOH) and hydrogen gas (H₂).

Increasing Reactivity

As you move down Group 1, the reactivity of the alkali metals increases. This trend occurs because the outermost electron is further away from the nucleus, experiencing weaker attractive forces. Consequently, the outer electron is easier to remove, leading to greater reactivity.

Predicting Properties from Trends

Properties within Group 1 can be predicted based on trends as you move down the group:

• Atomic Size: Atomic size generally increases as you move down the group. This is because each alkali metal has an additional energy level or shell, resulting in larger atomic radii. The larger the atom, the more spread out the outer electron is from the nucleus.
• Electronegativity: Electronegativity, which measures an element's ability to attract electrons, decreases as you move down Group 1. Alkali metals have relatively low electronegativity since the outer electron is relatively far from the nucleus and experiences weaker attractive forces.
• Reactivity: Reactivity increases as you move down the group. Alkali metals at the top of Group 1, such as lithium (Li) and sodium (Na), are less reactive compared to those at the bottom of the group, such as potassium (K) and cesium (Cs). The increase in reactivity is due to the larger atomic size and weaker attractive forces on the outer electron, making it easier to remove.

Example Predictions

Let's make predictions about the properties of alkali metals based on trends within Group 1:

• Atomic Size: As you move down the group, the atomic size increases. For example, lithium (Li) has a smaller atomic size compared to sodium (Na), and sodium has a smaller atomic size compared to potassium (K).
• Reactivity: Reactivity increases as you move down the group. For example, potassium (K) is more reactive than sodium (Na), and sodium is more reactive than lithium (Li).
• Density: Density generally increases as you move down the group due to the increase in atomic mass. For example, potassium (K) has a higher density than sodium (Na), and sodium has a higher density than lithium (Li).

Conclusion

In conclusion, alkali metals in Group 1 of the periodic table exhibit characteristic properties due to the presence of a single electron in their outer shell. Alkali metals are highly reactive, and their reactivity increases as you move down the group. They react vigorously with oxygen, chlorine, and water to form metal oxides, metal chlorides, and metal hydroxides, respectively.