Group 2: the alkaline earth metalsIB MYP Chemistry: Revision notes
Section 1
Where are the alkaline earth metals?
Group 2 contains beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), plus radium. Each atom has two electrons in its outer shell. They react by losing both to form ions with a charge of 2+, such as Mg²⁺ and Ca²⁺.
The compounds of these metals make alkaline solutions (hence the name 'alkaline earth').
Section 2
Physical properties
Group 2 metals are shiny when clean and are solids at room temperature. Compared with Group 1 metals they are harder, denser and have higher melting points. For example magnesium melts at about 650 °C but sodium melts at about 98 °C.
They are still fairly reactive, but less reactive than the Group 1 metal in the same row of the table, as two electrons must be lost.
Compare with Group 1: Group 2 metals are harder, denser and melt at higher temperatures.
Section 3
Reactivity increases down the group
Going down Group 2 (Mg, Ca, Sr, Ba):
- there are more electron shells
- the two outer electrons are further from the nucleus and more shielded
- the attraction is weaker, so the electrons are lost more easily
- reactivity increases
Calcium is more reactive than magnesium, and barium is more reactive than calcium.
Do not mix up the trends. Group 2 reactivity increases down the group, just like Group 1.
Section 4
Reactions with oxygen and water
With oxygen the metals form white oxides. Magnesium burns with a bright white flame:
2Mg + O₂ → 2MgO
With water, reactivity depends on the metal:
- Magnesium reacts only very slowly with cold water, but reacts when heated in steam to give magnesium oxide and hydrogen: Mg + H₂O → MgO + H₂
- Calcium fizzes in cold water, giving a cloudy solution of calcium hydroxide: Ca + 2H₂O → Ca(OH)₂ + H₂
- Strontium and barium react more vigorously still.
The hydroxide solutions are alkaline.
Section 5
Reactions with dilute acid
Group 2 metals react with dilute acids to give a salt and hydrogen:
metal + acid → salt + hydrogen
Mg + 2HCl → MgCl₂ + H₂
Ca + 2HCl → CaCl₂ + H₂
Mg + H₂SO₄ → MgSO₄ + H₂
The reactions are faster and produce more bubbles of hydrogen going down the group, so calcium reacts more vigorously than magnesium.
Balance chlorides carefully: each Group 2 ion is 2+, so it needs two chloride ions, giving MgCl₂ and CaCl₂.
Section 6
Uses of magnesium and calcium compounds
Magnesium
- the metal is used in light alloys and in fireworks and flares (bright white light)
- magnesium oxide has a very high melting point and lines furnaces
- magnesium hydroxide is in indigestion remedies because it neutralises stomach acid
Calcium
- calcium carbonate (limestone) is used in building materials and cement, and in some antacid tablets
- calcium oxide and calcium hydroxide (lime) neutralise acidic soil
- calcium compounds make up bones and teeth
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Group 2: the alkaline earth metals
- A firework designer in Valencia uses magnesium powder to produce a brilliant white light in a display rocket. Magnesium is a Group 2 metal, and the powder burns in the oxygen of the air.Write the balanced symbol equation for magnesium burning in oxygen.2 marks
- A class adds a small piece of calcium to cold water in a beaker containing universal indicator. The calcium sinks, fizzes steadily, and the water turns cloudy and then purple. In a second beaker, a clean strip of magnesium ribbon in cold water produces only a few tiny bubbles over several minutes.Explain why calcium reacts more vigorously with water than magnesium.2 marks
- A student compares magnesium and calcium by reacting each with dilute hydrochloric acid and collecting the hydrogen in a gas syringe for 60 s. She uses the same mass of metal, 25 cm³ of the same acid and the same temperature, and repeats each test twice. Magnesium gave 16 cm³ and 20 cm³. Calcium gave 58 cm³ and 62 cm³. The magnesium was a ribbon strip and the calcium was small granules. Her hypothesis was that calcium is more reactive than magnesium.Calculate the mean volume of hydrogen for each metal and state whether the results support her hypothesis.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).