group 2 elements
TRANSCRIPT
Group 2 Elements
HISYAMUDIN
MAC ALISTER
Introduction
Groups 2 elements are:
1) Consist of 6 elements2) S-block elements3) Known as alkaline earth metals
Z Element No. of electrons/shell
4 Beryllium 2, 2
12 Magnesium 2, 8, 2
20 Calcium 2, 8, 8, 2
38 Strontium 2, 8, 18, 8, 2
56 Barium 2, 8, 18, 18, 8, 2
88 Radium 2, 8, 18, 32, 18, 8, 2
The elements of Group 2, the Alkaline Earth Metals, are:
symbol electron configuration
beryllium Be [He]2s2 magnesium Mg [Ne]3s2 calcium Ca [Ar]4s2 strontium Sr [Kr]5s2 barium Ba [Xe]6s2 radium Ra [Rn]7s2
Beryllium
Magnesium
Calcium
Barium
Physical Properties• Atomic radii• Ionisation energy• Melting point• Standard Electrode Potential
Physical Properties
Element Colour
Mg brilliant white
Ca brick-red
Sr crimson
Ba apple green
Atomic radius
the atomic radius increases as going down the Group.
The radius of an atom is governed by:
• the number of layers of electrons around the nucleus.
Ionisation Energy
The decrease in first ionisation energy
Ionisation energy is governed by:
• the amount of screening by the inner electrons,
• the distance between the outer electrons and the nucleus
Melting Point
Standard Electrode Potential
Element Be Mg Ca Sr Ba
Eᶲ/V -1.85 -2.37 -2.87 -2.89 -2.90
• All the Eᶲ values are negative
• This show that the group 2 element are strong reducing agents (electron donor)
Chemical properties
REACTIONS WITH WATER
Beryllium
• no reaction with water or steam even at red heat.
Magnesium
• burns in steam to produce magnesium oxide and hydrogen.
• Mg(s) + H2O(g) MgO(s) + H2(g)
Calcium• react rapidly with hot water
Strontium and barium• with cold water with increasing vigour to give
the metal hydroxide and hydrogen.
• X(s) + 2H2O(l) X(OH)2 (aq or s) + H2(g)
REACTIONS WITH OXYGEN
• the metals burn in oxygen to form a simple metal oxide which are white solids.
2X(s) + O2(g) 2XO(s)
• The oxides dissolve in water to form the respective hydroxides.
MO(s) + H2O(l) M(OH)2(aq)
Thermal decomposition
• The nitrates
• The carbonates
• The hydroxides
• Examples: • 2Mg(NO₃)₂(s) → 2MgO(s) + 4NO₂(g) + O₂• (brown fumes)• MgCO₃(s) → MgO(s) + CO₂(g)
• Mg(OH)₂(s) → MgO(s) + H₂O(l)
The effect of heat on the Group 2 carbonates
• All the carbonates give the metal oxide and carbon dioxide.
• If "X" represents any one of the elements:
• Going down the Group, the carbonates have to be heated more strongly before they will decompose.
• The carbonates become more stable to heat as going down the Group.
The effect of heat on the Group 2 nitrates
• All the nitrates give the metal oxide, nitrogen dioxide and oxygen after been heated.
• Again, if "X" represents any one of the elements:
• As going down the Group, the nitrates also have to be heated more strongly before they will decompose.
• The nitrates also become more stable to heat as go down the Group.
Solubility of Group 2 Sulphates
• BeSO₄ and MgSO₄ are soluble in water.
• CaSO₄ and SrSO₄ are sparingly soluble in water.
• Barium sulphate is insoluble in water.
Question
a. Explainsi. First ionisation energy of group 2.ii. Atomic radius of group 2. b. The nitrates of the group 2 elements decompose
on heating liberate a brown fumei. state the indentity of the brown fumeii. Write a balanced equation for the thermal
decomposition magnesium nitrate
THANK YOU