Calcium vs Strontium
Both are alkaline earth metals, so they share the same broad chemistry.
The differences in plain English
- They sit in the same column, group 2, so they have the same number of outer electrons and react in similar ways; the heavier one, Strontium, is usually the more reactive of the two if they are metals, and the less reactive if they are non-metals.
- Both are solids at room temperature.
- Strontium is denser, about 70 per cent more than Calcium (2.64 against 1.55 g/cm³).
- Calcium melts at 842 °C, Strontium at 777 °C.
- An atom of Strontium is about 2.2 times heavier than an atom of Calcium (87.62 u against 40.08 u).
- Calcium pulls electrons more strongly in a bond (electronegativity 1 against 0.95).
Side by side
| Calcium | Strontium | |
|---|---|---|
| Atomic number | 20 | 38 |
| Symbol | Ca | Sr |
| Family | Alkaline earth metal | Alkaline earth metal |
| Group / period | 2 / 4 | 2 / 5 |
| State at room temperature | Solid | Solid |
| Atomic mass | 40.078 u | 87.621 u |
| Density | 1.55 g/cm³ | 2.64 g/cm³ |
| Melting point | 842 °C | 777 °C |
| Boiling point | 1484 °C | 1377 °C |
| Electronegativity | 1 | 0.95 |
| First ionisation energy | 589.8 kJ/mol | 549.5 kJ/mol |
| Electron configuration | [Ar] 4s2 | [Kr] 5s2 |
| Discovered by | Humphry Davy | William Cruickshank (chemist) |
Calcium
You are carrying about a kilogram of calcium, almost all of it in your bones and teeth. Yet calcium the metal is something few people ever see: a soft, silvery solid that fizzes gently in water and dulls quickly in air. The metal is a curiosity. Its compounds are everywhere, in chalk, limestone, marble, seashells, cement, plaster and indigestion tablets.
- Cement manufacture is one of the largest single industrial sources of carbon dioxide, because heating limestone drives off the gas chemically as well as burning fuel.
- Calcium colours a flame brick red, which is how it shows up in a flame test and in some fireworks.
Strontium
Strontium is the only element named after a place in the United Kingdom. The lead mines at Strontian, a small village on the west coast of the Scottish Highlands, produced an unusual mineral in the 1780s, and the metal inside it was named accordingly. It is a soft, silvery alkaline earth metal that behaves so much like calcium that the human body cannot tell them apart.
- Strontium is the only element named after a place in the United Kingdom: Strontian, a village in the Scottish Highlands.
- A survey of baby teeth in St Louis found strontium-90 from nuclear tests rising year by year, which helped bring about the 1963 Partial Test Ban Treaty.
Colour the bubbles by density or melting point and the difference jumps out.
More comparisons
Data from Periodic-Table-JSON (CC BY-SA); temperatures rounded to the nearest degree. Written by Anthony.