In simple terms
A friendly intro before the formal notes — no formulas yet.
Group 2: Down the Group Trends
Group 2 elements, the alkaline earth metals, show predictable changes in their properties as you go down the group. These trends, from reactivity to solubility, are all explained by the increasing size of the atoms and ions.
Imagine trying to pull a small electron 'bead' away from a central 'nucleus' magnet. If you add layers of 'cushions' (electron shells) between them, the pull gets weaker and it's easier to remove the bead. This is like ionisation energy decreasing down Group 2, making the elements more reactive.
- 1
A Level Group 2: solubility SO₄²⁻ ↓, OH⁻ ↑ down group. | Sim hint: BaSO₄ insoluble — barium meal.
- 2
Thermal stability CO₃²⁻ and NO₃⁻ increases down group. | Sim hint: Decomposition temperature trend.
- 3
Complex ion formation less central than transition metals. | Sim hint: Contrast with d-block chemistry.
- 4
Link to lattice energy and ionic radius arguments. | Sim hint: Born–Haber style reasoning at A Level.
Explore the concept
Use the live diagram and synced steps — play it or tap a step card to walk through.
Key formulas
Tap any symbol to reveal exactly what it means and its units.
Full topic notes
Formal explanation with the rigour you need for the exam.
Trends in Atomic and Physical Properties
As we descend Group 2 from Mg to Ba, several key properties change in a predictable manner. The atomic radius increases because each successive element adds a new principal quantum shell of electrons. This has a knock-on effect on other properties.
Atomic Radius: Increases down the group due to the addition of electron shells.
First Ionisation Energy: Decreases down the group. The outermost electrons are further from the nucleus and experience increased shielding from inner shells, making them easier to remove despite the increasing nuclear charge.
Melting Point: Generally decreases down the group, but the trend is not perfectly regular (Magnesium is an anomaly). This is because the metallic bonding gets weaker as the atomic size increases and the distance between the positive nuclei and the delocalised electrons increases.
Reactivity: Increases down the group. The lower ionisation energy means it is easier for the atoms to lose their two valence electrons and form a 2+ ion.
Solubility of Group 2 Compounds
The solubility of Group 2 compounds shows two important, opposing trends. For a salt to dissolve, the hydration enthalpy of the ions must be more exothermic than the lattice energy. Both these values decrease down the group, but at different rates for different anions.
Hydroxides, M(OH)₂: Solubility increases down the group. Magnesium hydroxide is 'sparingly soluble' (often described as insoluble in introductory contexts), while barium hydroxide is much more soluble.
Sulfates, MSO₄: Solubility decreases down the group. Magnesium sulfate (Epsom salts) is very soluble, while barium sulfate is famously insoluble. This is why adding acidified barium chloride or barium nitrate is the test for sulfate ions.
Explanation: The differing trends are due to the relative changes in lattice enthalpy and hydration enthalpy down the group. For sulfates, the lattice enthalpy decreases less rapidly than the hydration enthalpy, making dissolution less favourable down the group. The reverse is true for hydroxides.
Thermal Stability of Carbonates and Nitrates
Thermal stability refers to the resistance of a compound to break down upon heating. For Group 2 carbonates and nitrates, their stability increases significantly as you go down the group. This trend is explained by the polarising power of the cation.
Decomposition of Carbonates:
Decomposition of Nitrates:
The key to explaining this trend is charge density. A small, highly charged cation like has a high charge density and a strong polarising effect. It distorts the electron cloud of the large carbonate () or nitrate () anion, weakening the internal covalent bonds (e.g., C-O bonds) and making decomposition easier. The larger ion has a lower charge density, polarises the anion less, and so the compound is more thermally stable.
When explaining trends in thermal stability, always structure your answer clearly. Start with the trend in ionic radius of the cation, link this to the trend in charge density and polarising power, and finally explain how this affects the stability of the anion and the compound as a whole. Simply stating 'stability increases' will not earn full marks.
Worked examples
See the formulas applied — reveal one step at a time, like the exam.
A student has two unlabelled test tubes, one containing aqueous magnesium nitrate and the other containing aqueous barium nitrate. Describe a simple chemical test to distinguish between the two solutions. Include the expected observations and an ionic equation.
- 1
Reagent: Add a few drops of dilute sulfuric acid, , or aqueous sodium sulfate, , to each test tube.
Compare the temperatures at which magnesium carbonate and calcium carbonate decompose. Explain your answer in terms of the properties of the cations.
- 1
Comparison: Magnesium carbonate decomposes at a lower temperature than calcium carbonate. (e.g., at ~350°C, at ~840°C). Therefore, calcium carbonate is more thermally stable.
How it all connects
The big idea sits in the middle — tap a linked idea to explore the link.
Tap a linked idea to see how it connects back to the main topic — that connection is what examiners reward.
Glossary
Try to recall each definition before you reveal it.
Quick check
Answer in your head first — then tap to check. No pressure.
Revision flashcards
Flip the card. Test yourself before the exam.
What are the elements in Group 2 of the periodic table called?
The alkaline earth metals.
Key takeaways
Review these before you close the topic — retrieval beats re-reading.
- ✓
Atomic Radius: Increases down the group due to the addition of electron shells.
- ✓
First Ionisation Energy: Decreases down the group. The outermost electrons are further from the nucleus and experience increased shielding from inner shells, making them easier to remove despite the increasing nuclear charge.
- ✓
Melting Point: Generally decreases down the group, but the trend is not perfectly regular (Magnesium is an anomaly). This is because the metallic bonding gets weaker as the atomic size increases and the distance between the positive nuclei and the delocalised electrons increases.
- ✓
Reactivity: Increases down the group. The lower ionisation energy means it is easier for the atoms to lose their two valence electrons and form a 2+ ion.
Practice — then mark it
The whole point: a real Cambridge question, marked mark-by-mark.
Test Your Knowledge on Group 2 Trends
Test Your Knowledge on Group 2 Trends
Extra simulations & links
PhET, GeoGebra and other curated tools — open in a new tab.
Frequently asked
Checkpoint
One marked question is worth ten re-reads — close the loop before you move on.
Reading it isn’t knowing it — prove it.
Before you move on: do Test Your Knowledge on Group 2 Trends on paper, snap a photo, and get examiner-style feedback on exactly where you win and lose marks.