2.2 Group 2 - Melting points, ionisation energy and reactions - Revision guide

Aug 26, 2026

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Revision notes on Group 2 (alkaline earth) trends, linking melting points and 1st ionisation energy to atomic size, electron shell shielding and weakened metallic bonding. Covers typical reactions with oxygen, explaining formation of magnesium oxide, reactivity increasing down the group, and the role of oxide removal for fair rate experiments. Includes reactions with acids and water/steam, hydroxide solubility trends, observations such as fizzing and precipitation, and applications such as using Mg(OH)2 in medicine and steps for extracting titanium using magnesium.

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2.2 Group 2

Melting points and bonding trends

1st ionisation energy trends

Reactions with oxygen

Reactions with acids and water

Solubility of hydroxides and sulphates

Solubility tests and observations

Using magnesium to extract titanium

2.2 Group 2 Melting points Down the group the melting points decrease. The metallic bonding weakens as the atomic size increases. The distance between the positive ions and delocalized electrons increases. Therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken. 1st ionisation energy The outermost electrons are held more weakly because they are successively further from the nucleus in additional shells. In addition, the outer shell electrons become more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons Group 2 reactions Reactions with oxygen. The group 2 metals will burn in oxygen. Mg burns with a bright white flame. 2Mg + O2 􏃠 2MgO MgO is a white solid with a high melting point due to its ionic bonding. Reactivity of group 2 metals increases down the group Mg will also react slowly with oxygen without a flame. Mg ribbon will often have a thin layer of magnesium oxide on it formed by reaction with oxygen. 2Mg + O2 􏃠 2MgO This needs to be cleaned off by emery paper before doing reactions with Mg ribbon. If testing for reaction rates with Mg and acid, an un-cleaned Mg ribbon would give a false result because both the Mg and MgO would react but at different rates. Mg + 2HCl 􏃠 MgCl2 + H2 MgO + 2HCl 􏃠 MgCl2 + H2O Reactions with water. Magnesium burns in steam to produce magnesium oxide and hydrogen. The Mg would burn with a bright white flame. Mg (s) + H2O (g) 􏃠 MgO (s) + H2 (g) Mg will also react with warm water, giving a different magnesium hydroxide product. Mg + 2 H2O 􏃠 Mg(OH)2 + H2 This is a much slower reaction than the reaction with steam and there is no flame. Make sure you learn the difference between the reaction of Magnesium with steam and that of warm water The other group 2 metals will react with cold water with increasing vigour down the group to form hydroxides. Ca + 2 H2O ( l) 􏃠 Ca(OH)2 (aq) + H2 (g) Sr + 2 H2O ( l) 􏃠 Sr(OH)2 (aq) + H2 (g) Ba + 2 H2O ( l) 􏃠 Ba(OH)2 (aq) + H2 (g) The hydroxides produced make the water alkaline (if they are soluble in water) One would observe: fizzing, (more vigorous down group) the metal dissolving, (faster down group) the solution heating up (more down group) and with calcium a white precipitate appearing (less precipitate forms down group) [N Goalby chemrevise.org](N Goalby chemrevise.org) 1 Using Magnesium to Extract titanium Titanium is a very useful metal because it is abundant, has a low density and is corrosion resistant – it is used for making strong, light alloys for use in aircraft for example. Titanium is extracted by reaction with amore reactive metal (e.g. Mg, Na) . Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium (similar reactions take place for vanadium, tungsten and molybdenum) . Titanium cannot be extracted by electrolysis because it has to be very pure. Steps in extracting Titanium 1. TiO2 (solid) is converted to TiCl4 (liquid) at 900 C: 2. The TiCl4 is purified by fractional distillation in an Ar atmosphere. 3. The Ti is extracted by Mg in an Ar atmosphere at 500 C Titanium is expensive because 1. The expensive cost of the Mg 2. This is a batch process which makes it expensive because the process is slower (having to fill up and empty reactors takes time) and requires more labour and the energy is lost when thereactor is cooled down after stopping 3. The process is also expensive due to the Ar, and the need to remove moisture (as TiCl4 is susceptible to hydrolysis) . 4. High temperatures required in both steps TiO2 + 2 Cl2 + 2 C TiCl4 + 2 CO TiCl4 + 2Mg Ti + 2 MgCl2 TiO2 is converted to TiCl4 as it can be purified by fractional distillation, TiCl4 being molecular (liquid at room temperature) rather than ionic like TiO2 (solid at room temperature) . This all makes titanium expensive even though it is a relatively abundant m

FAQs

Why do melting points decrease down Group 2?

As atomic size increases, metallic bonding weakens: the distance between positive ions and delocalised electrons increases, reducing electrostatic attraction.

How does Group 2 reactivity change when going down the group?

Reactivity increases down the group. For example, magnesium burns more readily, and other Group 2 metals react more vigorously with cold water to form hydroxides.

What are the key differences between magnesium reacting with steam and with warm water?

With steam, magnesium burns with a bright white flame and forms magnesium oxide and hydrogen. With warm water, the reaction is much slower, produces magnesium hydroxide, and there is no flame.

Aug 26, 2026

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