Alkaline Earth Metal
Alkaline earth metals are the six elements of Group 2 of the periodic table — beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) — each with two valence electrons that are lost to form 2+ cations. They are harder and denser than alkali metals, with higher melting points, and they react with water (though less vigorously than Group 1) to form alkaline hydroxide solutions. Calcium and magnesium are biologically essential; calcium is the primary mineral in bones and teeth, while magnesium is a cofactor for hundreds of enzymatic reactions.
Key Formula
M(s) + 2H2O(l) → M(OH)2(aq) + H2(g)
LaTeX: \text{M}(s) + \text{2H}_2\text{O}(l) \rightarrow \text{M(OH)}_2(aq) + \text{H}_2(g)
| Symbol | Meaning | Unit |
|---|---|---|
| M | Alkaline earth metal (Ca, Mg, Ba, etc.) | — |
| M(OH)2 | Metal hydroxide formed | — |
| H2 | Hydrogen gas released | — |
Worked Example
Problem
Calculate the mass of calcium hydroxide formed when 20 g of calcium reacts completely with excess water.
Solution
Step 1 – Balanced equation: Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) Step 2 – Moles of Ca: Molar mass of Ca = 40 g/mol n(Ca) = 20 g ÷ 40 g/mol = 0.5 mol Step 3 – Moles of Ca(OH)2: 1:1 ratio, so n(Ca(OH)2) = 0.5 mol Step 4 – Molar mass of Ca(OH)2: 40 + 2(16+1) = 40 + 34 = 74 g/mol Step 5 – Mass: m = 0.5 mol × 74 g/mol = 37 g
Answer
37 g of calcium hydroxide
Properties of alkaline earth metals
| Element | Symbol | Atomic No. | Melting Point (°C) | Key Use |
|---|---|---|---|---|
| Beryllium | Be | 4 | 1287 | Aerospace alloys |
| Magnesium | Mg | 12 | 650 | Antacids, alloys |
| Calcium | Ca | 20 | 842 | Bones, cement |
| Strontium | Sr | 38 | 777 | Fireworks (red colour) |
| Barium | Ba | 56 | 727 | X-ray contrast agent |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Alkali Metal
Alkali metals are the six elements of Group 1 of the periodic table — lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr) — each having a single valence electron that is readily lost to form a +1 cation. They are soft, shiny, highly reactive metals that react vigorously with water to produce a metal hydroxide and hydrogen gas, with reactivity increasing down the group. Alkali metals are found widely in nature as salts and are essential to biological processes; sodium and potassium ions, for example, regulate nerve impulse transmission in living organisms.
Chemical Group
A chemical group (also called a family) is a vertical column in the periodic table containing elements that share the same number of valence electrons, and therefore exhibit similar chemical properties and reactivity patterns. The modern IUPAC system numbers groups 1 through 18 from left to right. Elements within a group show predictable trends: for example, reactivity increases down Group 1 (alkali metals) because the outermost electron is progressively further from the nucleus and more easily lost.
Periodic Trend
Periodic trends are systematic patterns in elemental properties that arise from the regular variation in nuclear charge and electron configuration across periods and down groups of the periodic table. Key periodic trends include atomic radius, ionisation energy, electron affinity, electronegativity, and metallic character, all of which change predictably as atomic number increases. Understanding periodic trends allows chemists to predict chemical reactivity, bond types, and physical properties of elements and their compounds without needing to memorise individual data for every element.
From Arabic "al-qaly" (alkali) + Latin "terra" (earth). The name reflects that these oxides (earths) were alkaline but did not dissolve readily in water, unlike alkali metal oxides. The term "alkaline earth" was used by 18th-century chemists before the elements themselves were isolated.