ElementsWhat are the alkaline earth metals?
The alkaline earth metals fill the second column. They are harder and less reactive than the alkali metals next to them, but still too reactive to be found pure in nature. Each atom has two outer electrons. Their compounds are common in rocks: limestone, chalk and marble are calcium carbonate. Calcium and magnesium are needed by all living things. Several of them give strong colours to flames, which is why they are used in fireworks.
The family in numbers
Melting points in this family run from 649.9 °C (magnesium) to 1,287 °C (beryllium). Among its solid members, the least dense is calcium (1.54 g/cm³) and the densest is radium (5 g/cm³). The most recently discovered member is radium (1898).
How the family changes down the column
Like their neighbours in group 1, the alkaline earth metals become more reactive going down. Beryllium hardly reacts with water at all. Magnesium reacts slowly with cold water and briskly with steam. Calcium fizzes steadily in cold water, and barium more strongly still. Each atom gives up its two outer electrons when it reacts, so the family forms compounds of the same pattern: MgO, CaO, BaO.
Flame colours and fireworks
Calcium compounds colour a flame brick red, strontium compounds a deep crimson and barium compounds apple green. These are the reds and greens of fireworks. Magnesium metal burns with a dazzling white light and is used in flares and sparklers.
Where you meet them
Calcium is the metal of bones, teeth, eggshells and sea shells, and of limestone, marble, chalk, cement and plaster. Magnesium sits at the centre of chlorophyll, the green substance with which plants catch sunlight, and its light, strong alloys are used in aircraft and laptops. The word "earth" in the name is an old chemists' word for substances that did not melt or change in a fire, as the oxides of these metals do not. Radium, at the foot of the column, is strongly radioactive.
All alkaline earth metals compared
| No. | Symbol | Name | Atomic mass | State | Melts at | Boils at | Density g/cm³ | Discovered |
|---|---|---|---|---|---|---|---|---|
| 4 | Be | Beryllium | 9.012183 | Solid | 1,287 °C | 2,471 °C | 1.85 | 1798 |
| 12 | Mg | Magnesium | 24.305 | Solid | 649.9 °C | 1,090 °C | 1.74 | 1808 |
| 20 | Ca | Calcium | 40.08 | Solid | 841.9 °C | 1,484 °C | 1.54 | 1808 |
| 38 | Sr | Strontium | 87.62 | Solid | 776.9 °C | 1,382 °C | 2.64 | 1790 |
| 56 | Ba | Barium | 137.33 | Solid | 726.9 °C | 1,897 °C | 3.62 | 1808 |
| 88 | Ra | Radium | 226.02541 | Solid | 699.9 °C | 1,140 °C | 5 | 1898 |
Other families: alkali metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, noble gases, lanthanides, actinides.