The Six Alkali Metals Discoveries are recent. Sodium and potassium (1807) by ______________. Cesium (1860) and rubidium (1861) from emission spectra. Francium (1939) from actinium radioactive decay.
Most salts are water ____________. Natural brines are good sources. Natural deposits allow mining of solids. Soft and silvery
The Six Alkali Metals Melting point, boiling point and density are low (for a metal): Melting Point
Boiling Point
Density (at 20 °C)
Lithium
180.54 °C
1347 °C
0.534 g/cm3
Sodium
97.81 °C
883.0 °C
0.971 g/cm3
Potassium
63.65 °C
773.9 °C
0.862 g/cm3
Rubidium
39.05 °C
687.9 °C
1.532 g/cm3
Cesium
28.4 °C
678.5 °C
1.873 g/cm3
Typically stored under _____ because they react with air (both oxygen and water vapor) 3
Common Chemical Behavior Valence electron configuration, ns1 Low first ionization energy Only forms one cation, M+1 Excellent reducing agent (good at losing electrons so that other elements can be reduced)
4
First Ionization Energy (kJ/mol)
Standard Reduction Potential (V = J/C)
Lithium
520.2
-3.040
Sodium
495.8
-2.713
Potassium
418.8
-2.924
Rubidium
403.0
-2.924
Cesium
375.7
-2.923
Practice Which of the following statements is false for the alkali metals. 1. As you go down group 1, the metals become more reactive with the halides. 2. Na has a higher ionization energy than K.
Sodium metal.
3. The melting points decrease as you go down the group. 4. These metals all have two valence electrons in s orbitals. 5. Ionic compounds composed of these metals are quite soluble in water. 5
Different Flame and Temper How can I distinguish between the alkali metals? _________. All of the alkali metals give positive flame tests. Complete the table below after doing the Metals Lab. Reactivity with _________. All of the alkali metals react exothermically with water to give the corresponding hydroxide and hydrogen gas. For safety reasons, you will only test small amounts of sodium and potassium in the Metals Lab. Flame Colour
Strength of Reaction with Water*
Lithium Sodium Potassium Rubidium Cesium 6
*Video:
Bluish red Blue http://www.youtube.com/watch?v=Ft4E1eCUItI&mode=related&search=
And Form Different Oxides Reaction with oxygen produces several ionic oxides.
In limited oxygen supplies: ________ (small amounts of Li2O2 from Li) Potassium, rubidium and cesium cannot be stopped at the oxide – only at the peroxide. Write an equation for the formation of Na2O:
Slide 7
General Chemistry: Chapter 21
With Excess Oxygen Lithium reacts with excess oxygen to give lithium oxide: Sodium reacts with excess oxygen to give sodium peroxide: Potassium, rubidium and cesium all react with excess oxygen to give the corresponding superoxide:
8
They Also Explode with Halogens Alkali metals also react vigorously with halogens:
_______are formed. What types of compounds are these salts? How about their solubility in water? Video: http://www.angelo.edu/faculty/kboudrea/demos/sodium_chlorine/sodium_chlorine.htm 9
The Dissolving Process What happens to the crystal of sodium chloride? NaCl(s) + H2O(l) -> NaCl(aq) (not a chemical eq.) Dissolving is a physical process: Na
+
Cl Cl
+ + Cl + +
Na
Na
Na
+
+ +
+
Na +
+
+
Na
+
A solvated, or hydrated cation, Na(OH2)6+(aq) or Na+(aq) 10
+
+ +
+
Before dissolving
+
+
Cl
+
Cl
After dissolving
+
Cl +
+
A solvated, or hydrated anion, Cl(OH2)6-(aq) or Cl-(aq)
For this process to be spontaneous, energy must be released.
The Solvation Stabilization For an ionic compound to be soluble in water, the solvated ions must be more stable (lower energy) than the initial crystal lattice so that energy is released. Alkali metals have large hydration enthalpies. (The beaker gets ______ when NaOH is dissolved in H2O!)
M ( s) M (aq) H hyd ____ 0(usually)
Exothermic process.
The metal ion is said to be stabilized by solvation (hydration) 11
Now We Can Explain the Li Anomaly Based on the data given to the right, the oxidation of Li in the presence of water to produce aqueous lithium ions is due mainly to the highly exothermic _________ of lithium ions.
subHo
ionHo
hydHo
rHo
Li
159
520
-510
169
Na
108
496
-410
194
K
89
419
-336
172
M(s) M(g)
sub H o
M(g) M + (g) + e
ion H o
M + (g) M + (aq)
hyd H o
M(s) M + (aq) + e
rHo
Why Li+ gets extra stabilization? The lithium cation’s small size (only 59 pm – remember that the electron configuration of Li+ is _________) allows the oxygen atoms of the surrounding water molecules to approach more closely than they could for a larger cation. Li is the best reducing reagent. First Ionization Energy (kJ/mol)
Standard Reduction Potential (V = J/C)
Lithium
520.2
-3.040
Sodium
495.8
-2.713
Potassium
418.8
-2.924
Rubidium
403.0
-2.924
Cesium
375.7
-2.923
13
Hydration Doesn’t Just Happen in Water Effect of Moisture Blue anhydrous
Quantitatively Speaking A 3 mm cube of sodium metal is added to 100 mL of distilled water in a beaker. When the reaction has completed, what is the concentration of the resulting sodium hydroxide solution? Assume that no water evaporates.
15
Quantitatively Speaking A 3 mm cube of sodium metal is added to 100 mL of distilled water in a beaker. When the reaction has completed, what is the concentration of the resulting sodium hydroxide solution? Assume that no water evaporates.
16
Names and Formulas of Inorganic Compounds Binary Compounds of Metals and Nonmetals
Naming Transition Metal Ionic Compounds Give both the systematic and the older names for the following: Indicate oxidation state for multi-oxidation state ions. systematic
older
AuCl
Aurous chloride
Fe2O3
Ferric oxide
FeCl2
Ferrous chloride
19
Practice Name the following: KF Li3N RbI
Name the following:
TiCl3 CuO Cu2O CaBr2 20
Practice
The molecular formula of the ionic compounds that calcium forms between CO32- and PO43- are
1. CaCO3 and Ca3(PO4)2 2. Ca(CO3)2 and Ca2(PO4)3
3. Ca2CO3 and Ca3PO4 4. Ca2(CO3)3 and CaPO4 5. Ca2(CO3)2 and Ca3(PO4)2
