Group 1A and 2A Reactions: Videos & Practice Problems

Alkali metals (group 1A) and alkaline earth metals (group 2A) react vigorously with water, producing hydrogen gas (H₂) and metal hydroxides in highly exothermic reactions. For example, the reaction of a group 1A metal with water can be represented as: $2_M+2H₂\to 2_{\mathrm{MOH}}+H₂$. Both groups also form ionic halides when reacting with halogens, such as $M+2X\to {\mathrm{MX}}_{₂}$ for group 2A metals.

Reaction with H2O

Alkali metals, found in group 1A of the periodic table, and alkaline earth metals from group 2A, are known for their vigorous reactions, particularly with water and halogens from group 7A. When these metals react with water, the reactions are highly exothermic, meaning they release a significant amount of heat, characterized by a negative change in enthalpy (ΔH).

In the case of alkali metals reacting with water, the general reaction can be represented as follows:

For a group 1A metal (M):

2 M + 2 H₂O → 2 M⁺¹ + 2 OH^- + H₂↑

Here, M represents the alkali metal, which forms a metal ion with a +1 charge, along with hydroxide ions (OH^-) and hydrogen gas (H₂). The reaction is balanced by ensuring that there are equal numbers of each type of atom on both sides of the equation. For alkaline earth metals in group 2A, the metal would produce a +2 ion instead, leading to a slightly different stoichiometry in the balanced equation.

Overall, the reactions of these metals with water are not only rapid but also produce hydrogen gas, which can be observed as bubbles during the reaction, further emphasizing the reactivity of these elements.

Group 1A and 2A Reactions Example

In the reaction between solid potassium (K) and liquid water (H₂O), a series of products are formed, illustrating a classic example of an alkali metal reacting with water. The balanced chemical equation for this reaction can be expressed as:

2 K (s) + 2 H₂O (l) → 2 K⁺ (aq) + 2 OH⁻ (aq) + H₂ (g) + heat

In this reaction, two moles of potassium react with two moles of water, resulting in the formation of two moles of potassium ions (K⁺), two moles of hydroxide ions (OH⁻), and hydrogen gas (H₂). The reaction is exothermic, meaning it releases heat as a product. This release of heat is significant, as it can lead to vigorous reactions, especially with alkali metals like potassium.

Understanding this reaction is crucial, as it highlights the reactivity of alkali metals and the nature of exothermic processes in chemical reactions.

Alkaline earth metals react with certain substances to produce hydrogen gas. Which of the following will result in hydrogen gas formation? Provide a balanced reaction.
a) Beryllium (Be) and O₂
b) Barium (Ba) and CO₂
c) Calcium (Ca) and H₂O
d) Strontium (Sr) and O₂

• A. Beryllium (Be) and O₂
  2 Be(s) + O₂(g) → 2 BeO(s)
• B. Barium (Ba) and CO₂
  Ba(s) + 2 CO₂(g) → BaO(s) + CO(g) + heat
• C. Calcium (Ca) and H₂O
  Ca(s) + 2 H₂O(l) → H₂(g) + Ca²⁺(aq) + 2 OH^–(aq) + heat
• D. Strontium (Sr) and O₂
  2 Sr(s) + O₂(g) → 2 SrO(s)

Answer: (C)

Reaction with Halogens

In chemical reactions involving halogens, both Group 1A (alkali metals) and Group 2A (alkaline earth metals) react with diatomic halogens to form ionic halides. When a Group 1A metal, represented as \( M \), reacts with a diatomic halogen (e.g., \( \text{Cl}_2 \)), the resulting ionic halide can be expressed as \( MX \). Here, the metal \( M \) has a charge of +1, while the halogen, being in Group 7A, has a charge of -1. The charges balance each other out, leading to the formation of the ionic compound.

For example, if we consider the reaction:

\[ 2M + \text{Cl}_2 \rightarrow 2MX \]

In this equation, the coefficient of 2 is necessary to balance the two chlorine atoms from the diatomic halogen, which results in two metal ions on the product side.

Similarly, when a Group 2A metal, which has a charge of +2, reacts with a halogen, the product formed is \( MX_2 \). In this case, the reaction can be represented as:

\[ M + \text{Cl}_2 \rightarrow MX_2 \]

Here, the +2 charge of the Group 2A metal balances with the -1 charge of two halogen atoms, resulting in the formation of the ionic compound \( MX_2 \).

In summary, both Group 1A and Group 2A metals react with diatomic halogens to produce ionic halides, with the need to balance the overall reaction as necessary.

Group 1A and 2A Reactions Example

When lithium, a Group 1A element with a +1 oxidation state, reacts with diatomic fluorine gas (F₂), which has a -1 oxidation state, the product formed is lithium fluoride (LiF). The balanced chemical equation for this reaction is crucial to ensure that the number of atoms for each element is equal on both sides of the equation.To balance the reaction, we start with the unbalanced equation:\[\text{Li (s)} + \text{F}_2 (g) \rightarrow \text{LiF (s)}\]Since each molecule of fluorine gas contains two fluorine atoms, we need two lithium atoms to react with it. Therefore, we place a coefficient of 2 in front of both lithium and lithium fluoride:\[2 \text{Li (s)} + \text{F}_2 (g) \rightarrow 2 \text{LiF (s)}\]This balanced equation indicates that two moles of solid lithium react with one mole of diatomic fluorine gas to produce two moles of lithium fluoride. Balancing chemical equations is essential for understanding stoichiometry, which allows us to predict the amounts of reactants and products involved in a chemical reaction.

Provide the products from the reaction between strontium and aqueous chlorine.

• A. SrCl(s)
• B. Sr₂Cl₃(s)
• C. Sr₂Cl(s)
• D. SrCl₂(s)

Answer: (D)

Here’s what students ask on this topic:

What happens when Group 1A metals react with water?

When Group 1A metals react with water, they undergo a highly exothermic reaction, producing hydrogen gas (H₂) and a metal hydroxide. The general reaction can be represented as:

$M\left(s\right)+2H2O\left(l\right)\to M\mathrm{OH}\left(\mathrm{aq}\right)+H2\left(g\right)$

Here, M represents a Group 1A metal, such as lithium (Li), sodium (Na), or potassium (K). The metal hydroxide formed is in aqueous form, and hydrogen gas is released. This reaction is highly exothermic, meaning it releases a significant amount of heat.

How do Group 2A metals react with water?

Group 2A metals react with water to form hydrogen gas (H₂) and a metal hydroxide, similar to Group 1A metals, but with a different stoichiometry. The general reaction can be represented as:

$M\left(s\right)+2H2O\left(l\right)\to M\left(\mathrm{OH}\right)2\left(\mathrm{aq}\right)+H2\left(g\right)$

Here, M represents a Group 2A metal, such as magnesium (Mg) or calcium (Ca). The metal hydroxide formed is in aqueous form, and hydrogen gas is released. This reaction is also exothermic, releasing heat.

What products are formed when Group 1A and 2A metals react with halogens?

When Group 1A and 2A metals react with halogens, they form ionic halides. For Group 1A metals, the reaction with a diatomic halogen (X₂) produces an ionic halide (MX). The general reaction is:

$2M\left(s\right)+X2\left(g\right)\to 2\mathrm{MX}\left(s\right)$

For Group 2A metals, the reaction with a diatomic halogen produces an ionic halide (MX₂). The general reaction is:

$M\left(s\right)+2X2\left(g\right)\to \mathrm{MX}2\left(s\right)$

Here, M represents a Group 1A or 2A metal, and X represents a halogen, such as fluorine (F₂), chlorine (Cl₂), bromine (Br₂), or iodine (I₂).

Why are reactions of Group 1A and 2A metals with water highly exothermic?

Reactions of Group 1A and 2A metals with water are highly exothermic because they release a significant amount of energy in the form of heat. This is due to the formation of strong bonds in the products (metal hydroxides and hydrogen gas) and the breaking of weaker bonds in the reactants (metal and water). The overall enthalpy change (ΔH) for these reactions is negative, indicating that energy is released. The exothermic nature of these reactions can be observed through the vigorous release of hydrogen gas and the increase in temperature of the reaction mixture.

How do you balance the chemical equations for reactions of Group 1A and 2A metals with halogens?

To balance the chemical equations for reactions of Group 1A and 2A metals with halogens, you need to ensure the conservation of mass and charge. For Group 1A metals reacting with halogens, the general equation is:

$2M\left(s\right)+X2\left(g\right)\to 2\mathrm{MX}\left(s\right)$

For Group 2A metals, the general equation is:

$M\left(s\right)+2X2\left(g\right)\to \mathrm{MX}2\left(s\right)$

Here, M represents a Group 1A or 2A metal, and X represents a halogen. Ensure the number of atoms of each element is the same on both sides of the equation. Adjust coefficients as necessary to balance the equation.