Alkali and Alkaline Earth Metals

Flashcards: Alkali and Alkaline Earth Metals

Alkali Metals

S-block elements with the outer electron in an s-orbital. They react by losing an electron to produce M+ ions and are reducing agents.

Ionization Energy (Alkali Metals)

Decreases down the group due to increased shielding and distance between the nucleus and outer electron, resulting in increased reactivity.

Physical Properties of Alkali Metals

Soft metals with low densities, low melting points due to weaker metallic bonding, good conductors of heat and electricity.

Reaction of Alkali Metals with Water

Vigorous reaction with cold water to produce an alkaline solution and hydrogen gas.

Reaction of Alkali Metals with Oxygen

Lithium burns with a red flame to produce lithium oxide. Sodium burns with a yellow flame to produce sodium oxide and sodium peroxide. Potassium burns with a lilac flame to produce peroxide and superoxide.

Polarizing Power (Alkali Metals)

The tendency to form peroxides and superoxides increases down the group due to a decrease in the polarizing power of the cation.

Alkali Metal Hydroxides

Prepared by reacting the metal, oxide, or hydride with water. Soluble, with solubility increasing down the group. Solid hydroxides are deliquescent.

Thermal Stability of Group 1 Hydroxides

Increases down the group, with lithium hydroxide decomposing at 650°C to produce oxide and water vapor.

Alkali Metal Carbonates

Prepared by bubbling carbon dioxide through a solution of the alkali. Thermally stable except for lithium carbonate, which decomposes to give the oxide and carbon dioxide.

Efflorescence

The property of sodium carbonate-10-water crystals, which lose some or all of their water of crystallization without being heated.

Thermal Stability of Carbonates

Increases down the group due to a decrease in the q/r of the positive ion.

Alkali Metal Hydrogencarbonates

Prepared by bubbling excess carbon dioxide through a solution of the carbonate. Decompose when heated to produce a carbonate, water vapor, and carbon dioxide.

Alkali Metal Nitrates(V)

Break down when heated to produce a nitrate(III) and oxygen, except lithium nitrate, which breaks down to give lithium oxide, nitrogen dioxide, and oxygen.

Alkaline Earth Metals

Group 2 elements that form ionic compounds in which they are found as M2+ ions.

Beryllium

An amphoteric metal that reacts with both acids and alkalis to give a salt and hydrogen. Its compounds have covalent character, and Be2+ solutions are acidic.

Lattice Enthalpies (Group 2)

Higher for Group 2 than Group 1 compounds due to a higher q/r of their cation.

Thermal Stability (Group 2)

Group 2 compounds are more thermally unstable than corresponding Group 1 compounds due to a greater polarizing power of the cation.

Physical Properties of Alkaline Earth Metals

Silvery grey metals with higher melting points and densities than alkali metals due to stronger metallic bonding; good conductors of heat and electricity.

Reaction of Alkaline Earth Metals with Oxygen

Burn vigorously in air to produce a simple oxide, except barium, which tends to form the peroxide. They also form nitrides when heated in air.

Reaction of Alkaline Earth Metals with Water

Beryllium does not react with cold water or steam but reacts with acids. Magnesium reacts slowly with cold water but immediately with steam. Calcium reacts steadily with cold water. Strontium and barium react more vigorously.

Solubility of Group 2 Hydroxides

Increases down the Group due to a decrease in lattice dissociation enthalpy.

Thermal Stability of Group 2 Hydroxides

Increases down the Group due to a decrease in q/r of the cation.

Solubility of Group 2 Carbonates

Insoluble and prepared by precipitation. Their solubility decreases down the Group.

Thermal Decomposition of Group 2 carbonantes

Carbonates break down when heated to give the oxide and carbon dioxide.

Group 2 Hydrogencarbonates

Less stable than those of Group 1, found only in solution, and break down when heated to give a solid carbonate, water, and carbon dioxide.

Solubility of Group 2 Sulfates(VI)

Solubility decreases down the group.

Group 2 Nitrates(V)

Soluble and prepared by reacting dilute nitric acid with a metal oxide, hydroxide, or carbonate. They break down when heated to give an oxide, nitrogen dioxide, and oxygen.