Group 2: Properties, Reactions of Elements and Compounds, Trends

Introduction

Group 2 of the periodic table consists of alkaline earth metals: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra). These elements share similar chemical properties due to having two valence electrons.

Properties of Group 2 Elements

Physical Properties

• Metallic: They are lustrous, silvery-white metals.
• Relatively low density compared to other metals.
• Malleable and ductile (though less so than alkali metals).
• Lower melting and boiling points compared to alkali metals.
• Not very reactive at room temperature.

Chemical Properties

• Tend to lose two electrons to form $2^+$ cations.
• React with oxygen to form oxides.
• React with water (though reactivity increases down the group).
• React with acids.
• Form ionic compounds.

Reactions of Group 2 Elements

Reaction with Water

The reactivity of Group 2 metals with water increases down the group. The reaction produces hydrogen gas and a hydroxide solution.

$M(s) + 2H_2O(l) \rightarrow M(OH)_2(aq) + H_2(g)$

Reaction with Oxygen

Group 2 metals react with oxygen at high temperatures to form oxides. The oxides formed are typically basic in nature.

$M(s) + O_2(g) \rightarrow MO_2(s)$

Reaction with Acids

Group 2 metals react with dilute acids to form salts and hydrogen gas.

$M(s) + 2HCl(aq) \rightarrow MCl_2(aq) + H_2(g)$

Trends in Properties

Atomic Radius

Atomic radius increases down the group. This is due to the addition of electron shells.

Ionization Energy

Ionization energy decreases down the group. This is because the outermost electrons are further from the nucleus and are shielded by more inner electrons.

Electronegativity

Electronegativity decreases down the group. This is because the attraction for electrons weakens with increasing distance from the nucleus.

Metallic Character

Metallic character increases down the group. This is due to the decreasing ionization energy and increasing tendency to lose electrons.

Trends in Oxide Properties

Basicity

The basicity of oxides decreases down the group. This is because the $M^{2+}$ cation has a smaller charge density, leading to a weaker interaction with water.

$M_2O_n(s) + nH_2O(l) \rightarrow 2M(OH)_n(aq)$

Specific Compounds

Magnesium Oxide ($MgO$)

A strong ionic compound with a high melting point. It is a stable white solid.

Magnesium Chloride ($MgCl_2$)

A soluble ionic compound used in various applications.

Calcium Carbonate ($CaCO_3$)

A common mineral found in limestone and chalk. It decomposes on heating to form calcium oxide and carbon dioxide.

$CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$

Applications of Group 2 Compounds

• Magnesium: Used in alloys, fireworks, and as a reducing agent.
• Calcium: Essential for bones and teeth, used in cement production.
• Strontium: Used in fireworks for red colour.
• Barium: Used in luminous paints and in the manufacture of glass.

Element	Symbol	Atomic Number	Reactivity with Water	Oxide Formula	Oxide Basicity
Beryllium	Be	4	Very Low	$BeO$	Amphoteric
Magnesium	Mg	12	Low	$MgO$	Basic
Calcium	Ca	20	Moderate	$CaO$	Basic
Strontium	Sr	38	Moderate	$SrO$	Basic
Barium	Ba	56	High	$BaO$	Basic
Radium	Ra	88	Very High	$RaO$	Basic