2. Group 2, alkaline earth metals Flashcards
What are the elements in group 2 called?
The alkaline earth metals
What is atomic radius?
The distance from the centre of the nucleus to the outer electrons
What happens to atomic radii down group II?
It increases
Why does atomic radius increase down group II?
- more shells as you move down the group
- so increased distance from nucleus
- so atomic radius ↑
What is the first ionisation energy?
The enthalpy change when 1 mole of gaseous atoms forms one mole of positive gaseous atoms (by losing 1 mole of electrons)
What happens to first ionisation energy down group II?
Decreases
Why does first ionisation energy decrease down group II?
- more shells down group
- outer electrons so ↑ distance from nucleus
- so increased shielding
- so weaker attraction for outer electrons
What is melting point?
The point at which sufficient bonds are broken/loosened within the substance so that the solid and liquid phase are in equilibrium
What happens to the melting point down group II?
Decreases
Why does melting point decrease down group II?
- Metals held by metallic bonds
* Atomic radii ↑ down group but same number of delocalised electrons = less attraction between metal ions and electrons
What is the irregularity in the trend that melting point decreases down group II?
Mg
Why is Mg an irregularity in the trend that melting point decreases down group II?
It has a different crystal structure from the other elements, which is less packed and therefore easier to separate
Which group II compounds react with water?
All of them
What do group II compounds react with water to produce?
The metal hydroxide and hydrogen
What is the rate of reaction when Mg reacts with water?
Very slow
What is the equation for the reaction of Mg with water?
Mg₍ₛ₎ + H₂O₍ₗ₎ → Mg(OH)₂₍ₐᵩ₎ + H₂₍𝓰₎
What happens when Mg is heated in steam?
It will burn to form an oxide
What is the equation for the reaction of Mg with steam?
Mg₍ₛ₎ + H₂O₍𝓰₎ → MgO₍ₛ₎ + H₂₍𝓰₎
For group II elements, from calcium to barium, how do they react with cold water down the group?
React with increasing vigour down the group
Why do group II elements, from calcium to barium, react more vigorously with water down the group?
- more likely to lose electrons
- larger atom/more shells
- greater distance from nucleus to outer electrons
- ↑ shielding
- easier to lose outer electrons
What is solubility?
The maximum amount of solute that will dissolve in a given volume of solvent
(i.e. how easily it dissolves)
How soluble is something when it is ‘sparingly soluble’?
Not very soluble
Why is Mg(OH)₂ considered to be sparingly soluble?
A very small amount of it dissolves, giving a suspension of magnesium hydroxide in water (milk of magnesia)
How is milk of magnesia formed?
Magnesium hydroxide is dissolved, giving a suspension in water
How soluble is Mg(OH)₂?
Sparingly
How soluble is Ca(OH)₂?
Quite - dissolves almost fully in water
What happens when calcium hydroxide is added to water?
It dissolves almost fully to form lime water
What happens when barium/strontium hydroxide are added to water?
They both dissolve to produce strongly alkaline solutions - OH- fully dissociates
What happens when elements below barium in group II are added to water?
They dissolve easily and form clear solutions
What happens to the solubility of the hydroxides down group II?
It increases
What happens to the solubility of the sulphates down group II?
It decreases
What is barium sulphate used to test for?
The presence of sulphate ions
Why is barium sulphate used to test for sulphate ions?
Solubility of the sulphates decreases down group Ii
What does barium chloride form in the presence of sulphate ions?
White precipitate
How is the sulphate test carried out?
- Add HCl to solution being tested
2. Add aqueous barium chloride - if sulphate ions present, then white precipitate of barium sulphate forms
Why is HCl added in the sulphate test?
Removes any other ions that could give a precipitate with barium chloride e.g. carbonate ions
When HCl is added in the sulphate test, what is formed as a result?
CO₂ and H₂O
What is the solubility of BaCl₂ like in water?
Very soluble
Equation for sulphate test, with magnesium sulphate?
BaCl₂ + MgSO₄ → BaSO₄ + MgCl₂
What is Mg(OH)₂ used for?
- laxative - relieve constipation - ↑ water in intestines
* antacid - relieve indigestion and heart burn
What is Ca(OH)₂ used for?
↑ PH level in the soil into the optimal range (6-7) - for plant growth and uptake of nutrients (also known as hydrated lime)
What is BaSO₄ used for?
- used in medical imaging of the gastrointestinal tract as it is opaque to X-rays
- BaSO₄ solution ingested by patient, covers oesophagus, stomach and intestines
Why is BaSO₄ used for barium meals?
Other Ba compounds are toxic, and other group II metal compounds are soluble
What is CaO or CaCO₃ used for?
To remove SO₂ produced in burning fuels
What is Mg used for?
In the extraction of Ti from TiCl₄:
TiO₂ converted to TiCl₄ by heating with carbon and chlorine. TiCl₄ then reduced by Mg
Equation for reduction of TiCl₄ by Mg?
TiCl₄ + 2Mg → Ti + 2MgCl₂
