Group 2

In 2020, the Spitzer Space Telescope was retired by NASA after 17 years of service. It had observed the universe's infrared activity, providing us with a unique insight into previously hidden areas of space. It carried instruments that could detect wavelengths all the way from just 3.6 μm up to 160 μm in length, and used a mirror almost 1 metre in diameter to focus and reflect light. This mirror was cooled to a chilly 5.5 K - that's -268 °C!

But that's not the reason why it catches our interest. No, we care more about what it was built from. The mirror was made of beryllium, an example of a group 2 element.

Group 2 metals

• This article is about group 2 in inorganic chemistry.
• We'll start by providing an overview of the elements found in group 2.
• We'll then look at the properties of group 2 elements, including their atomic radius and first ionisation energy.
• After that, we'll explore how they react.
• Finally, we'll go over how to test for group 2 elements.

Group 2 elements

Take a look at the periodic table below. The column in pink shows you one particular group, group 2.

Group 2 in the periodic table. Olive, StudySmarter Originals

Group 2 contains six elements:

• Beryllium (Be)
• Magnesium (Mg)
• Calcium (Ca)
• Strontium (Sr)
• Barium (Ba)
• Radium (Ra)

These elements all appear in nature, although barium is never found on its own due to its high reactivity. Likewise, radium is extremely radioactive, and only occurs as part of the decay chains of heavier elements such as thorium and uranium.

Properties of group 2

Group 2 elements are fairly similar. Physically, they are all soft, shiny, silvery-white metals, with relatively low melting and boiling points and densities. Let's take a look at some of their other properties in more detail.

Group 2 structure and bonding

All group 2 elements have two electrons in their outer shell. These electrons are found in an outer s-orbital.

The electron configuration of magnesium. Created using images from commons.wikimedia.org

When they react, group 2 elements lose their two outer electrons to form cations with a charge of 2+, and an oxidation state of +2. This means that group 2 elements form ionic compounds.

Group 2 atomic radius

If you've read Periodic Trends, you should be able to predict how the atomic radius of group 2 elements varies as you move down the group. As you can see in the graph below, atomic radius increases moving down the group. This is because each subsequent element has more electrons, with more electron shells.

The atomic radius of group 2 elements. Anna Brewer, StudySmarter Originals

We've already seen the electronic structure of magnesium: it has 12 electrons found in three electron shells. The next element in the group, calcium, has 20 electrons found in four electron shells. It, therefore, has a larger atomic radius.

Magnesium and calcium. Created using images from commons.wikimedia.org

Group 2 melting points

In general, the melting points of group 2 elements decrease as you move down the group. As solids, metals form metallic lattices consisting of positive metal cations surrounded by a sea of negative delocalised electrons, as shown below.

Calcium's metallic lattice. Anna Brewer, StudySmarter Originals

This lattice is held together by strong electrostatic attraction between the negative electrons and the nuclei of the positive cations. Remember that atomic radius increases as you move down the group. This means that the nuclei are further away from the delocalised electrons. Therefore, the electrostatic attraction is weaker. So, less energy is needed to overcome it and melt the solid.

The melting points of group 2 elements. Anna Brewer, StudySmarter Originals

Group 2 first ionisation energy

We'll now move on to looking at the first ionisation energies of group 2 elements.

Can you guess the trend?

First ionisation energy decreases as you go down group 2. Once again, this is due to increasing atomic radius. As you move down the group, the outermost electron is further away from the nucleus. This means that the attraction between the nucleus and the electron is weaker, hence easier to overcome.

The first ionisation energy of group 2 elements. Anna Brewer, StudySmarter Originals

Group 2 electronegativity

Now let's look at electronegativity.

Once again, there is much more detail in Polarity. But the basic principles of electronegativity apply here too. Electronegativity decreases as you go down the group in the periodic table. As we know, atomic radius increases as you move down the group. This means that any bonded electrons are further from the nucleus, so the attraction between them is weaker.

Like all metals, group 2 elements are insoluble in water. However, their compounds have varying solubilities. (You can find out more in Group 2 Compounds.)

Group 2 reactivity

The final property we'll look at is reactivity. Like most metals, group 2 elements are fairly reactive. Their reactivity increases as you go down the group. As we explored earlier, group 2 elements (apart from beryllium) always react to form ions with a charge of 2+. This requires removing two outer shell electrons - in other words, the processes of first and second ionisation. Ionisation energy decreases as you go down the group, so it is easier to remove these electrons. Therefore, reactivity increases.

Reactions of group 2

Now that we've learnt about the properties of group 2, we can take a look at some of their reactions.

All reactions involving group 2 are redox reactions.

The group 2 element loses two electrons to form a cation with a charge of 2+, and an oxidation state of +2. It is oxidised. On the other hand, the other elements involved gain electrons. They are reduced. Don't worry - we'll practice showing this below.

Let's now explore the reactions of group 2 with water, oxygen, chlorine, and acids.

Group 2 elements' reaction with water

Have you ever wondered why group 2 are called the alkaline metals? It's because they react with water to produce alkaline metal hydroxides and hydrogen gas. This is a great example of the trend in reactivity of group 2 elements. Here, M represents the group 2 metal:

As with all reactions involving group 2 elements (apart from that sneaky beryllium), the reaction between a group 2 metal and water is a redox reaction. The group 2 metal is oxidised and loses electrons, whilst the hydrogen in water is reduced and gains an electron. The oxygen doesn't take part in the redox reaction - it is just a spectator species. We can show this using oxidation states.

The oxidation states in magnesium hydroxide. Anna Brewer, StudySmarter Originals

The reaction between a group 2 metal and water gets more vigorous as you go down the group. For example, magnesium reacts extremely slowly with water, producing just a few bubbles. You'd be hard-pressed to see any reaction at all. However, calcium fizzes gently when you add it to water, whilst strontium and barium bubble violently. Overall, their reactivity increases as you move down the group. Once again, this is because their ionisation energies decrease as you go down the group. Lower ionisation energies mean that it is easier to lose electrons, so reactivity increases.

Group 2 elements' reaction with oxygen

We'll now focus on the reaction between group 2 elements and oxygen. Burning a group 2 element in oxygen produces a metal oxide. Here's the equation:

The same reaction happens if you leave a group 2 metal exposed to air. A metal oxide rapidly builds up on the surface of the metal, producing a thin coating that stops any further reaction.

Strontium and barium also burn in oxygen to produce a peroxide, . However, beryllium, magnesium, and calcium don't. This has to do with the smaller size of these metal ions. Since they are smaller, they have a much higher charge density, attracting the oxygen molecules differently.

Group 2 elements' reaction with chlorine

Group 2 metals react with chlorine to produce metal chlorides. In fact, they react in a similar way with all halides. Once again, reactivity increases as you go down the group. Here's the general equation:

Group 2 elements' reaction with acids

Finally, we'll turn our attention to the reactions of group 2 with acids. These vary depending on the type of acid used.

Hydrochloric acid

This is the simplest case - the group 2 element reacts with hydrochloric acid to give a metal chloride and hydrogen gas. For example, mixing magnesium with hydrochloric acid gives magnesium chloride and hydrogen:

Nitric acid

Nitric acid makes things a little more complicated. Group 2 metals can also reduce the nitrogen atoms found within nitric acid, forming all manner of nitrous oxides. However, the main reaction produces a metal nitrate and hydrogen gas.

Sulphuric acid

Group 2 elements react with sulphuric acid to produce metal sulphates and hydrogen gas. However, in reality, strontium and barium don't tend to react much. This is because the sulphate forms an insoluble layer on the surface of the metal, preventing any further reaction. Likewise, calcium sulphate is only sparingly soluble, so calcium doesn't react much with sulphuric acid either. Nevertheless, here's the general reaction between a group 2 metal and sulphuric acid:

Group 2 summary

Here's a handy table that summarises the reactions of group 2 for you.

Testing for group 2

Right at the start of the article, we mentioned how all group 2 elements are pretty similar in appearance. They are all silvery metals. This can make them quite tricky to tell apart. However, one way of distinguishing group 2 metals is by putting them in a flame. The different metals burn to produce different-coloured flames in a spectacular show.

Get a clean metal loop and dip it in acid. Hold it in a Bunsen burner flame until there is no colour change. This cleans the loop. Next, dip the loop in a solid sample of your metal and hold it back in the Bunsen burner once again. Observe the colour of flame produced. With any luck, you'll get the following results.

Note that beryllium and magnesium don't produce a coloured flame. You'll have to rely on other chemical tests to tell them apart.

Uses of group 2 elements

Lastly, let's focus on some of the uses of group 2.

• Calcium is the fifth-most abundant element in the human body and plays a role in bone health, muscle contraction, and neurotransmission.
• Calcium compounds are used in agriculture to raise the pH of soil. They can also be used to remove sulphur from flue gas.
• Barium compounds are used in x-rays, and beryllium alloys are used in mechanical parts.
• Magnesium is the third-most commonly used structural metal, mostly used in lightweight alloys.