Group 2 Elements

• Elements in Group 1 and Group 2 are known as: s-block elements because their valence [bonding] electrons are in the s orbitals.

M  → M2+

+

2e-

• These elements give away 2 electrons when they react.
• As the Group 2 elements cause the reduction of other compounds or elements (as it gives two electrons to another compound), we say it is a good Reducing agent.
• Reactivity increases as you go down the Group.  This means they lose their electrons more readily.
• This means as you go down Group 2, they become better Reducing agents.

Physical Properties

• High melting and boiling points
• Low density metals
• Form colourless compounds/white when solid

Atomic Radius

The atomic radius increases as you go down the group due to:

• The increased number of electron shells
• The less effective nuclear attraction

1st Ionisation energy

The first ionisation energy decreases as you go down the group due to:

• despite the increased nuclear charge
• there is increased electron shielding
• the atomic radii increases
• Overall the effective nuclear attraction decreases.
• Become more reactive as you go down group 2.

Group 2 elements reacted with oxygen

• Group 2 metals react vigorously with oxygen to form simple ionic oxide

e.g. 2Mg (s) + O₂ (g) → MgO (s)

• It reacts with increasing vigour as you go down the group

Group 2 elements reacted with water

• Beryllium does not react with water
• The rest of the group 2 metals react with increasing vigour as you go down the group to form a metal hydroxide, M(OH)₂ and hydrogen gas

e.g. M (s) + 2H₂O (l) → M(OH)₂ (aq) + H₂ (g)

• These hydroxides have increasing solubility in water to form alkaline solutions.

Group 2 oxides and hydroxides
 

• Group 2 oxides and hydroxides are bases
• They are neutralised by acids to from a salt and water

e.g. MgO (s) + 2HCl (aq) → MgCl₂ (aq) + H₂O (l)
       Ca(OH)₂ (s) + 2HCl → CaCl₂ (aq) + H₂O (l)
 
Oxides

• Group 2 oxides react with water to form a solution of the metal hydroxide.
• These solutions usually have a pH of 10-12

e.g. MgO (s) + H₂O (l) → Mg(OH)₂ (aq)
 
Hydroxides

• Group 2 hydroxides dissolve in water to form alkaline solutions.

e.g. Ca(OH)₂ (s) + aq → Ca²⁺ (aq) + 2OH^- (aq)

• The solubility of the hydroxides in water increases as you go down the group.

Uses of group 2 hydroxides?
 
- Calcium hydroxide, Ca(OH)₂ is used by farmers and gardeners to neutralise acidic soils
- Magnesium hydroxide, Mg(OH)₂ is used in 'Milk of magnesia' to relieve indigestion. It works by neutralising any excess acid in the stomach.
 
Group 2 Metal Carbonates
 
THERMAL DECOMPOSITION is the breaking of a chemical substance using heat into at least 2 smaller substances.

• The group 2 carbonates undergo thermal decomposition to form the metal oxide and carbon dioxide gas.

 e.g. MgCO₃ (s) → MgO (s) + CO₂ (g)

• The group 2 carbonates decompose at a higher temperatures as you go down the group.

• e.g. BaCO₃ needs the most energy to break the bonds in the compound.

 

 

Calcium Compounds

 

 



 
 
- Most calcium is found as calcium carbonate in limestone
 
Uses of calcium compounds

• Limestone - Calcium carbonate CaCO₃ (s) - making cement
• Quicklime Calcium Oxide CaO (s) - iron purification
• Slaked Lime - Solid calcium hydroxide Ca(OH)₂ (s) - Soil Treatment
• Lime water - Aqueous calcium hydroxide Ca(OH)₂ (aq) - testing for CO₂

 

Come and Practice some Questions!

Hi to My Chemistry Club friends,

Today I am going to go over some common exam questions and in response there will be some model answers. I hope this helps get you ready for your F321 OCR A Chemistry exam, or just enlightens your chemistry knowledge :)

1. Define the term: Relative Atomic Mass? (3)

Relative Atomic Mass is the average mass of an atom compared to 1/12th the mass of an atom of carbon-12.

2. What is meant by an orbital? (1)

An orbital is a region that can hold up to two electrons with opposite spins.

3. MgCO₃ (s) --> MgO (s) + CO₂ (g)

    What type of reaction is this? (1)

Thermal Decomposition

4. The student did an experiment another three times, using CaCO₃, SrCO₃ and BaCO₃. What trend in the behaviour of the group 2 carbonates would be observed by the student? (1)

The ease of thermal decomposition decreases down the group.

 

5. Explain why NF₃has a permanent dipole? (2)

F Is more electronegative than N. Also the dipoles do not cancel out (as it is an asymmetrical shape).

6. Explain, in terms of the intermolecular forces present, why ICl has a higher boiling point than Cl₂? (2)

ICl has permanent dipole-dipole interactions and Cl₂ has only Van-der-Waals' forces. The forces are stronger in ICl and this is why it has a higher boiling point.

7. The hydrazine molecule, H₂N-NH₂, is covalent. Predict the H-N-H bond angle in a hydrazine molecule. Explain your answer. (4)

107 °

There are 3 bonding pairs and 1 lone pair. The electron pairs repel. However, the lone pairs repel more than the bonded pairs.

8. What is the name for NaClO? (1)

Sodium Chlorate (I)

[suffix -ate just means the chlorine has oxygen attached to it]

9. What is meant by the term electronegativity? (2)

It is the ability of an atom to attract electrons in a covalent bond.

10. Describe how Van-der-Waals' forces arise. (3)

There is an uneven distribution of electrons, this creates an instantaneous dipole. This then causes induced dipoles in neighbouring molecules.

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Here is a diagram to help explain question 10:

 

 

 

 

 

 

 

 

 

 

Thanks for reading today's blog post, but don't forget to subscribe so you do not miss any of my regular future posts!

Holly :)

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Here is a little bonus question:

State and explain the trend in the boiling points of chlorine, bromine and iodine. (3)

Chlorine has the lowest boiling point, followed by bromine and then iodine has the highest boiling point.

There is a greater number of electrons/stronger Van-der-Waals' forces in Iodine compared to Chlorine.

Therefore more energy is needed to break the Van-der-Waals' forces.