Group 2 Flashcards
What block do the group 2 elements exist in?
S-block
Physical properties of Group 2 metals
Atomic radius increases down the group
Ionic size increases down the group
Melting points decrease down the group
Chemical properties of Group 2 metals
Undergo redox reactions to form 2+ ions
Reactivity increases down the group
Ionisation energies decrease down the group
What is the relationship in terms of atomic radi between positively charged ions and atoms?
Smaller atomic radius in positivity charged ions
Nuclear charge exceeds the electronic charge
Electrons are pulled closer to nucleus
Why do melting points decrease down the group?
Metallic bonding gets weaker due to increased size and density
How do the ionisation energies of group 2 compare with group 1?
Higher due to there being more electrons to remove in a energy level
What is the trend, going down the group, when group 2 metals react with oxygen?
React with increasing vigour down the group
Equation for the reaction of Mg with O2 including state symbols
2Mg(s) + O2(g) –> 2MgO(s)
Ionic equations for the reaction of Mg with O2
Mg –> Mg2+ + 2e-
O + 2e- –> O2-
Trend, going down the group, of the reaction of group 2 metals with water
React with increasing vigour
Describe the reaction of Mg with cold water
Very slow
Give the equation of the reaction of Mg with cold water
Mg(s) + 2H20(l) –> Mg(OH)2(aq) + H2(g)
Give the equation of the reaction of Mg with steam
Mg(s) + H20(g) –> MgO(s) + H2(g)
Trend, going down the group, of the reaction of group 2 metals with dilute acid
React with increasing vigour down the group
What is produced when a group 2 metal reacts with an acid? Give an example
Salt + Hydrogen
Mg(s) + H2SO4(aq) –> MgSO4(aq) +H2(g)
Ca(s) + 2HCl(aq) –> CaCl2(aq) + H2
Compare the reaction of group 2 metal with water and group 2 metal with dilute acid
Reactions more vigorous with dilute acid
Ionic equation of Mg with acid
Mg(s) + 2H+(aq) –> Mg2+(aq) + H2(g)
What type of solids do group 2 oxides form?
Ionic
except for beryllium which has covalent character
Trend in solubility of group 2 hydroxides
Solubility increases down the group
Give the equation for the reaction of calcium oxide with water
CaO(s) + H20(l) –> Ca(OH)2(s)
What is the trend in basic strength down Group 2? Explain the trend
Basic strength increases due to the solubility of the hydroxides increasing
What is the trend, going down the group, of charge density of group 2 metal ions?
As metal ions get larger, charge density decreases
Use of Ca(OH)2
Farming:
Neutralises acidic soils
Use of Mg(OH)2
Used in toothpaste and indigestion tablets as an antiacid
What are Ca(OH)2 and Mg(OH)2 an example of?
Weak alkalis
Trend in the ease of decomposition of Group 2 carbonates going down the group
Decomposition becomes harder as you move down the group
Properties of Group 2 carbonates
Insoluble in water
Undergo thermal decomposition to produce an oxide and CO2
Give an equation showing the decomposition of a group 2 carbonate
MgCO3(s) –> MgO(s) + CO2(g)
Trend in solubility of group 2 sulfates going down the group
Decreases
What is the appearance of group 2 sulfates?
White, crystalline solids
Why does solubility of group 2 sulfates decrease down the group?
Little change in lattice energy
Cation gets larger so hydration enthalpy gets smaller
A larger cation has a lower charge density so is less attracted to water molecules
Describe the test for sulfates
Add dilute HCl to a sample of group 2 sulfate
Add a few drops of barium chloride solution
White precipitate of barium sulfate will appear if it is a sulfate
Why is acid added in the test for sulfates?
To prevent precipitation of other insoluble ions such as carbonate
Describe the appearance of the group 2 metals
Bright, silvery solids
Why do group 2 metals sometimes appear dull?
- A slow reaction happens between the metal and oxygen in the air
- This forms a surface coating of oxide which gives the dull colour
- It also prevents further reaction
Give the equation for the reaction between calcium and oxygen
2Ca(s) + O2(g) –> 2CaO(s)
Give the equation for the reaction of barium with chlorine
Ba(s) + Cl2(g) –> BaCl2(s)
How does milk of magnesia work?
Give the equation
- Contains a saturated solution of magnesium hydroxide with extra solid magnesium hydroxide
- This acts as an antiacid that neutralises excess stomach acid
Mg(OH)2 + 2HCl –> MgCl2 + 2H2O
Why do the hydroxide ions in milk of magnesia pose no risk to health?
-Low solubility of magnesium hydroxide means the concentration of OH- ions is very low
Give the equation for the reaction between calcium oxide and nitric acid
What type of reaction is it?
What observations can you make?
CaO + 2HNO3 –> Ca(NO3)2 + H2O
Neutralisation reaction
White solid goes to colourless solution
Give the equation for the reaction of calcium hydroxide with nitric acid
Ca(OH)2 + 2HNO3 –> Ca(NO3)2 + 2H2O
What are basic oxides?
Oxides of metals that react with water to form metal hydroxides and with acids to form salts and water
Give the equation in which limewater becomes cloudy
CO2(g) + Ca(OH)2(aq) –> CaCO3(s) + H20(l)
