Periodic Properties: Groups I and II
A.
Group I—The Alkali Metals
1. Elements and Symbols
a. Li = Lithium
b. Na = Sodium
c. K = Potassium
d. Rb = Rubidium
e. Cs = Cesium
2.
Ion. Energy(kJ/mol)
520
495
419
403
376
2nd Ion. En.
7300
4560
3052
2633
2230
Reactivity with water
a. These elements need to lose 1 e- to be like a Noble Gas
b. Losing electrons is called “oxidation”
c. Water can gain electrons (“reduction”)
d. 2 M0(s) + 2 H2O(l) ------> 2 MOH(aq) + H2(g)
e. Example: 2 Na0(s) + 2 H2O(l) ------> 2 NaOH(aq) + H2(g)
f. Reactions are violently exothermic
g. Basic solutions are formed
Sodium metal reacting with water
3. Reactions with Oxygen
a. 4Li + O2  2Li2O Lithium Oxide
[O2- is called oxide;]
b. 2Na + O2  Na2O2 Sodium Peroxide
[O22- is called peroxide]
c. K + O2  KO2 Potassium Superoxide [O2- is called superoxide]
d. Rb + O2  RbO2 Rubidium Superoxide
e. Cs + O2  CsO2 Cesium Superoxide
B. Group II—The Alkaline Earth Metals
1. Elements and Symbols
Ion. Energy(kJ/mol)
a. Be = Beryllium
900
b. Mg = Magnesium
738
c. Ca = Calcium
590
d. Sr = Strontium
550
e. Ba = Barium
503
2nd Ion. En.
1757
1450
1145
1064
965
2. Reactions with Oxygen
a. Much more predictable: 2 M0(s) + O2(g) ------> 2 MO(s)
b. 2 Ca0(s) + O2(g) ------> 2 CaO(s)
3. Reactivity with water
• These elements need to lose 2 e- to be like a Noble Gas
• M0(s) + 2 H2O(l) ------> M(OH)2(aq) + H2(g)
• Example: Mg0(s) + 2 H2O(l) ------> Mg(OH)2(aq) + H2(g)
• Reactions are slow, with some bubbling visible
• Basic solutions are formed
4. Reactivity with Acid
a. M0(s) + 2 HCl(aq) ------> 2 MCl2(aq) + H2(g)
b. Mg0(s) + 2 HCl(aq) ------> 2 MgCl2(aq) + H2(g)
C. Ionization Energy
1. The energy required to remove an e- from a gaseous element
2. X(g) + I.E. ------> X+(g) + e3. More reactive metals have lower Ionization Energies
4. Ionization Energy decreases down a Group—the electron being removed is
farther from the nucleus, thus easier to remove
5. Ca (I.E. = 590 kJ/mol) is more reactive than Mg (I.E. = 738 kJ/mol)
6. K (I.E. = 419 kJ/mol) is more reactive than Li (I.E. = 520 kJ/mol)
Calcium Metal
Reacting with
Water to Form
Bubbles of
Hydrogen Gas
D. Metal Oxides and Water
1. The Alkali and Alkaline Earth Metals react with water to make it basic
2. 2 Na0(s) + 2 H2O(l) ------> 2 NaOH(aq) + H2(g)
3. Mg0(s) + 2 H2O(l) ------> Mg(OH)2(aq) + H2(g)
4. The oxides of these metals also react with water to make basic solutions
5. 2KO2(s) + 2H2O(l) ------> 2KOH(aq) + O2(g) + H2O2(aq)
6. MgO(s) + H2O(l) ------> Mg(OH)2(aq)
E. Notes on Today’s Lab
1. Do the reactions in the hood: H2 is produced
2. Do Part A first (metal hardness); then use same piece for Part B (H2O rxn)
DON’T THROW METALS IN TRASH: THEY CAN CATCH ON FIRE
2 M0(s) + 2 ROH(l) ------> 2 M+OR-(aq) + H2(g)
3. Use the Bunsen burner in the hood to burn the Magnesium
4. Phenolpthalein is red under basic conditions
5. Orange pH paper turns blue under basic conditions
Incident: Sodium Metal-Solvent Fire