Group 1A and 2A Reactions - Online Tutor, Practice Problems & Exam Prep

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

Here we're going to say that alkaline metals, the elements in Group 1A and alkaline earth metals from group 2A, undergo numerous reactions. Now, the two types of reactions that we're going to pay attention to are those that have them reacting with either water or a halogen from group 7A.

Now here we take a look at the reaction with water. We're going to say both groups react violently with water and have high exothermic, so ΔH of hydration. Now recall when metals react with an acidic proton H₂ gas is formed. Here we have an example of a reaction of these metals with water and in particular we're looking at group 1A.

Now with group 1A, we're going to say that arm metal from group 1A reacts with water. It's going to generate H₂ gas. In addition to this, it would produce our metal ion, and since it's in Group 1A, it's plus one. If we're in Group 2A, it'd be +2 plus hydroxide ion, and we said that this is a highly exothermic reaction.

Remember, exothermic means we're releasing heat, so heat would be a product. Once we balance this out, we'd have to put a 2 here, here, here and here, and this would represent my balanced equation between the reaction of group 1A metal with water. Now remember M here could stand in for a group 1/8 or a group 28 metal.

Group 1A and 2A Reactions Example

Here it says we need to complete and balance the following reaction. So from group 18 we have potassium solid reacting with liquid water. Now from our example that we saw earlier, we know that this will produce H₂ gas.

We know that it will produce 2 moles of potassium ion aqueous, it will produce 2 hydroxide ions aqueous plus the generation of heat. It is an exothermic process, so heat would be a product.

Now in addition to this we'd have a 2 here and A₂ here to finish balancing out our reaction O. This would represent our complete imbalance reaction between the reaction between the reacting of potassium solid and liquid water.

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)

Reaction with Halogens

Now when it comes to the reaction with halogens, we're going to say both groups 1A and 2A react with halogens to produce ionic pallets. If we take a look here, if M here represents a group 1A metal, it reacts with a diatomic halogen to produce an ionic halid. Remember, group 1A is plus one in charge. Halogens are in Group 7A, so they're -1. The numbers are the same, so they just cancel out. So our ionic halid is MX.

We have to balance this out. There's two halogens here, but only one here. So I throw 2 here. But now I have two metals on the product side, so I'd have to put a 2 here. M could also represent a group 2A metal which have a charge of two plus or +2. They would still react with the halogen, which is -1 and create M2X2 solid as a product.

In that case, you get that as a product and you still have to balance out your overall reaction if necessary. So just remember group 1A and 2A metals react with diatomic halogens to produce ionic halts.

Group 1A and 2A Reactions Example

Here it's us to complete and balance the following reaction. Here we have lithium salt reactor with diatomic fluorine gas. So if we know here that lithium is in Group 1A, so it's plus one fluorine in Group 7-8, so it's -1. As a result, we create lithium fluoride.

We still have to balance this reaction, so I put a 2 here. So both sides have two fluorines and I'd have to put a 2 here so that both sides have two lithiums. This would represent our complete and balanced reaction between lithium fluoride well between lithium solid and fluorine gas into production of lithium fluoride.

2   Li (s) +   F 2   (g)   →   2   LiF (s)

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

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

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.