HS Chemistry - Periodic Table Trends

Group 2 Elements' Reactions

Overview of The Page

This page will cover:

• Common reactions among Group 2 elements.

The elements in Group $column$ 2 of the Periodic Table $aka the Beryllium Group, although you may also hear it referred to as the Magnesium Group, or even the Calcium Group$ exhibit specific properties and trends due to their similar electron configuration. They also react in similar ways, and trends can be seen in these reactions.

Reactivity

The reactivity of an element is its ability and tendency to react. Elements that have lower first ionization energies are easier to ionize, and thus react more readily. Thus, the reactivity of Group 2 elements increases down the Group.

Reactions With Oxygen

The general formula for a Group 2 element's reaction with Oxygen $we'll use Beryllium, but Beryllium can be substituted for any Group 2 element$ is:

2Be $s$ + O₂ $g$ → 2BeO $s$

A metal oxide is formed. This metal oxide is solid at room temperature, white in color, and insoluble in water. As the reactivity of Group 2 elements increases down the Group, these reactions become more energetic down the Group.

This reaction is exothermic - it releases heat. This heat is typically seen in the form of a flame. The color of this flame depends on what Group 2 metal is used:

• If Magnesium is used, a bright white flame will be seen.
• If Calcium is used, an orange-red flame will be seen.
• If Strontium is used, a solid red flame will be seen.
• If Barium is used, a solid green flame will be seen.

The color of flame present when Beryllium or Radium react with Oxygen will not be covered here.

Reactions With Water

The general formula for a Group 2 element's reaction with water $we'll use Beryllium, but Beryllium can be substituted for any Group 2 element$ is:

Be $s$ + 2H₂O $l$ → Be$OH$₂ $aq$ + H₂ $g$

A metal hydroxide and Hydrogen gas is formed. As the reactivity of Group 2 elements increases down the Group, these reactions become more energetic down the Group, and the metal hydroxide becomes more soluble.

However, when steam is used instead of liquid water, the reaction changes:

Be $s$ + H₂O $g$ → BeO $s$ + H₂ $g$

A metal oxide and Hydrogen gas is formed instead. As the reactivity of Group 2 elements increases down the Group, these reactions also become more energetic down the Group.

Reactions With Acids

There are three acids this topic will cover: hydrochloric acid, sulfuric acid, and nitric acid:

Hydrochloric Acid

The general formula for a Group 2 element's reaction with hydrochloric acid $we'll use Beryllium, but Beryllium can be substituted for any Group 2 element$ is:

Be $s$ + 2HCl $aq$ → BeCl₂ $aq$ + H₂ $g$

A metal chloride and Hydrogen gas is formed. As the reactivity of Group 2 elements increases down the Group, these reactions become more energetic down the Group, and the metal hydroxide becomes more soluble.

Sulfuric Acid

The general formula for a Group 2 element's reaction with sulfuric acid $we'll use Beryllium, but Beryllium can be substituted for any Group 2 element$ is:

Be $s$ + H₂SO₄ $aq$ → BeSO₄ $aq$ + H₂ $g$

A metal sulfate and Hydrogen gas is formed. As the reactivity of Group 2 elements increases down the Group, these reactions become more energetic down the Group, and the metal hydroxide becomes more soluble.

As you go further down the Group, the metal sulfate becomes less soluble $i.e. MgSO~4~ is less soluble than BeSO~4~, CaSO~4~ is less soluble than MgSO~4~, etc.$.

Nitric Acid

Group 2 reactions with nitric acid are more complicated, as the products of the reaction depend on the concentration of the nitric acid.

It should also be noted that it is not known for sure whether Beryllium reacts with nitric acid, so it will not be covered here.

The general formula for a Group 2 element's reaction with nitric acid $we'll use Calcium, but Calcium can be substituted for any Group 2 element aside from Beryllium$ depends on the concentration of nitric acid:

• Dilute Concentration of Nitric Acid:

  • Ca $s$ + 2HNO₃ $aq$ → Ca$NO~3~$₂ $aq$ + H₂ $g$

• Moderate Concentration of Nitric Acid:

  • 3Ca $s$ + 8HNO₃ $aq$ → 3Ca$NO~3~$₂ $aq$ + 2NO $g$ + 4H₂O $l$
  • The nitrogen monoxide $NO$ quickly reacts in the air to form nitrogen dioxide $NO~2~$. It's just that when the concentration of nitric acid is moderate, NO is first formed before it reacts to form NO₂, instead of forming NO₂ directly.

• High Concentration of Nitric Acid:

  • Ca $s$ + 4HNO₃ $aq$ → Ca$NO~3~$₂ $aq$ + 2NO₂ $g$ + 2H₂O $l$
  • When the concentration of nitric acid is high, NO₂ is directly formed, instead of NO being formed and then quickly reacting with the air to form NO₂

Group 2 Ionic Compounds

There are two different ionic compounds this topic will cover: hydroxides and carbonates.

Hydroxides

Group 2 hydroxides all have roughly the same formula $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

Be$OH$₂

The vast majority of hydroxides are insoluble, but Group 2 hydroxides are an exception. Except for Beryllium, all Group 2 hydroxides are soluble, and their solubility increases as you go further down the group.

The more soluble a metal hydroxide is, the more hydroxide $OH^\-^$ ions are dissolved in water, and the more basic $higher pH$ the resulting solution becomes.

Carbonates

Group 2 metals react with carbonate ions $CO~3~^2\-^$ to form carbonate compounds. Group 2 carbonates all have roughly the same formula $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

BeCO₃

Almost all carbonates are insoluble, and this applies to Group 2 carbonates as well. They are insoluble in water, and therefore do not react with water.

They do, however, react with $dilute$ acids. This reaction has the same formula for any Group 2 carbonate $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

BeCO₃ $s$ + 2HCl $aq$ → BeCl₂ + CO₂ + H₂O

A metal salt, CO₂, and H₂O are formed. In this case, since hydrochloric acid $HCl$ was used, a chloride $BeCl~2~$ was formed. However, if we used a different acid:

BeCO₃ $s$ + H₂SO₄ $aq$ → BeSO₄ + CO₂ + H₂O

A metal salt, CO₂, and H₂O are formed again. This time, the metal salt is a sulfate $BeSO~4~$, since sulfuric acid was used $H~2~SO~4~$. However, no matter which acid is used, when a Group 2 carbonate reacts with an acid, CO₂ and H₂O will be formed.

Thermal Decomposition

When certain Group 2 ionic compounds are heated, they decompose, or break down into simpler molecules. As heat is constantly required for the reaction to take place, thermal decomposition reactions are usually endothermic. This page will look at the thermal decomposition of Group 2 carbonates and nitrates.

Carbonates

Group 2 carbonates all have roughly the same formula $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

BeCO₃

When Group 2 carbonates are heated, they break down to form a Group 2 metal oxide and CO₂ $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

BeCO₃ → BeO + CO₂

Nitrates

The thermal decomposition of Group 2 nitrates is more complicated.

Group 2 nitrates all have roughly the same formula $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

Be$NO~3~$₂

When Group 2 nitrates are heated, they break down to form a Group 2 metal oxide, nitrogen dioxide, and oxygen gas $Beryllium is used for this example, but any Group 2 element can be used in Beryllium's place$:

2Be$NO~3~$₂ → 2BeO + 4NO₂ + O₂