The Alkaline Earth Metals Revision Notes for Leaving Cert Chemistry

The Alkaline Earth Metals

Introduction and location

The alkaline earth metals are found in Group 2 of the Periodic Table. These elements are called "alkaline earth metals" because they form alkaline (basic) solutions when they react with water.

infoNote

The name "alkaline earth metals" also comes from the fact that many of their compounds are found naturally in the Earth's crust, particularly in earth-like minerals and rocks.

The three main alkaline earth metals you need to know for your Leaving Cert are:

Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)

These metals have low ionisation energies and low electronegativity values, which means they readily form ionic compounds by losing their two outermost electrons.

Physical properties

All alkaline earth metals share similar physical characteristics that make them easily identifiable:

Physical state: All are solid at room temperature
Appearance: Shiny, silvery-looking metals
Conductivity: Good conductors of both electricity and heat
Reactivity: All are reactive elements, but they vary in how reactive they are

infoNote

The tendency to lose two electrons is a key feature of all the chemical reactions of the alkaline earth metals, including their reactions with oxygen, water and acids.

Chemical reactions and equations

Reactions with oxygen

All alkaline earth metals react with oxygen to form metal oxides:

lightbulbExample

Chemical Equations: Reactions with Oxygen

Beryllium: $2\text{Be} + \text{O}_2 \rightarrow 2\text{BeO}$ (beryllium oxide)
Magnesium: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$ (magnesium oxide)
Calcium: $2\text{Ca} + \text{O}_2 \rightarrow 2\text{CaO}$ (calcium oxide)

Reactions with water

The alkaline earth metals show different levels of reactivity with water:

Beryllium: No reaction with water
Magnesium: Reacts slowly with cold water but much faster with steam
- $\text{Mg} + 2\text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 + \text{H}_2$
Calcium: Reacts quickly with cold water
- $\text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2$

In these water reactions, hydrogen gas is produced along with the metal hydroxide.

Reactivity trends down the group

There is a clear pattern in reactivity as you move down Group 2:

chatImportant

Reactivity increases down the group: Be < Mg < Ca

This is a crucial trend that frequently appears in exams!

This increasing reactivity occurs because:

The atomic radius increases as you go down the group
The shielding effect of inner electrons increases
These two factors cause the first ionisation energy to decrease down the group
Therefore, the electrons in the outermost energy levels are more easily lost
This means the reactivity increases as you go down the group

Key characteristics summary

The properties of the alkaline earth metals demonstrate their unique position in the periodic table:

All alkaline earth metals are reactive elements because they have low first ionisation energy values, meaning they readily lose their two outermost electrons
They are less reactive than the alkali metals but still too reactive to occur freely in nature as pure metals
Instead, they are found in stable compounds such as magnesium oxide and calcium carbonate ( $\text{CaCO}_3$ ), which is commonly called limestone
Since alkaline earth metals have low ionisation energies and low electronegativity values, they readily form ionic compounds by losing their two outermost electrons

Important exam points

chatImportant

Critical Information for Exams

Beryllium is unique among the alkaline earth metals as it forms both ionic (e.g. in BeO) and covalent bonding (e.g. in $\text{BeCl}_2$ , the bonding is covalent with electronegativity difference = 1.57)
Remember that reactivity increases down the group - this is the opposite of what happens with ionisation energy
The chemical equations for reactions with oxygen and water are commonly asked in exams
Understanding the trend explanation (atomic radius, shielding effect, ionisation energy) is crucial for exam success

bookmarkSummary

Key Points to Remember:

Alkaline earth metals are Group 2 elements that readily lose two electrons to form ionic compounds
Physical properties: solid, shiny, good conductors of electricity and heat
Reactivity increases down the group: beryllium < magnesium < calcium
All react with oxygen to form oxides, but only magnesium and calcium react with water to produce hydrogen gas
The increasing reactivity trend is explained by decreasing ionisation energy down the group due to increasing atomic size and shielding effect

The Alkaline Earth Metals (Leaving Cert Chemistry): Revision Notes