Trends in Group 2: The Alkaline Earth Metals (AQA A-Level Chemistry): Revision Notes

2.2.1 Trends in Group 2: The Alkaline Earth Metals

Overview of Group 2 Elements

Group 2 elements, known as the alkaline earth metals, include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). These metals react by losing two electrons to form ( 2^+ ) ions, achieving a stable electron configuration.

Atomic Radius

The atomic radius of Group 2 elements increases as you move down the group.

Reasons

• Moving down the group, elements have more electron shells, which leads to a larger atomic radius.
• The increased distance between the nucleus and the outer electrons reduces the effective nuclear attraction.

Reactivity

The reactivity of Group 2 metals increases down the group.

Reasons

• Increased shielding: As the number of inner electron shells increases, the outer electrons experience more shielding from the nucleus, reducing the nuclear attraction.
• Easier loss of outer electrons: Due to greater shielding and atomic radius, the outermost electrons are more easily lost, making the metals more reactive.

First Ionisation Energy

The first ionisation energy decreases as you move down Group 2.

Reasons

• The atomic radius increases, meaning the outermost electrons are further from the nucleus and experience weaker attraction.
• Increased shielding by inner electrons makes it easier to remove the outer electrons, requiring less energy.

Melting Point

The melting points of Group 2 elements generally decrease down the group.

Reasons

• Group 2 elements have a metallic structure where positive metal ions are surrounded by a sea of delocalised electrons.
• As the atomic radius increases down the group, the ions become larger. This weakens the metallic bonds, as the attractive force must act over a greater distance.
• Weaker metallic bonding requires less energy to overcome, resulting in lower melting points.