The alkali metals are so called because their hydroxides, MOH, are all soluble bases in water (alkaline means basic)

Among the alkali metals, sodium and potassium are abundant and lithium, rubidium and cesium have lower abundance. Francium is highly radioactive.

Physical properties of the alkali metals

•They have a low density (Li, Na and K float on water) •They have low melting and boiling points •They are good conductors of heat and electricity

Low ionization energy and Electronegativity making it easy to remove electrons.

The alkali metal atoms have the largest size in their respective periods of the periodic table. Atomic radii and ionic radii increase with atomic number as we move from Li to Cs.

The alkali metals occur in Group I of the periodic table and so have an ionic charge of +1 in their compounds.

All the alkali metals are very reactive. None occurs as the free metal in nature. They must be stored under an inert substance, such as kerosene, because they react spontaneously and rapidly with the oxygen and water vapor in the air.

The alkali metals are all fairly soft and can be cut with a sharp knife. When freshly cut they are bright and shiny, but they soon take on a dull finish because of their reaction with air.

Methods for commercial production of alkali metals

The alkali metals can be obtained by electrolysis, which is a decomposition reaction driven by passing an electric current through molten mixtures or a solution.

For example, sodium metal is obtained by electrolysis of a molten sodium chloride.

)()(2)(2 2

600 gCllNalNaClo

Chemical properties of the alkali metals

The alkali metals react directly with all the nonmetals except the noble gases. The reactivity increases down the group. This reactivity increase is due to the increasing diameter of the atoms, so that the attractive forces on the one valence electron is much less, and it is free to leave. . The increasing reactivity of the alkali metals with atomic number is demonstrated in a specific manner by their reaction with water.

1. Reactions of the Alkali Metals with water

a. When metallic lithium reacts with water, hydrogen gas is evolved slowly, whereas sodium reacts vigorously with water.

22 222 HLiOHOHLi

22 222 HNaOHOHNa

Sodium reacts violently with water

b. The reaction of potassium with water produces a fire because the heat generated by the reaction is sufficient to ignite the hydrogen gas is evolved. Rubidium and cesium react with water with explosive violence.

22 222 HKOHOHK

22 222 HRbOHOHRb

Potassium reacts with water

Hydroxides of alkali metals The alkali hydroxides are a class of chemical compounds which are composed of an alkali metal cation and the hydroxide anion (OH), e.g., Lithium hydroxide (LiOH), Sodium hydroxide (NaOH).They all are basic in nature.

2. Reactions of the Alkali Metals with oxygen

All alkali metals will form oxides in the form of M2O, but only lithium will form this oxide in excess oxygen: Sodium in an excess of oxygen will form the peroxide:

OLiOLi 22 24

2222 ONaONa

Potassium, Rubidium and Cesium react with oxygen to form super-oxides with the general formula of MO2 for example potassium:

22 KOOK

The super-oxides release oxygen gas when they react with water or carbon dioxide gas. For this reason they are very useful in emergency breathers for fireman or emergency workers.

22222 222 OHOKOHOHKOairexhaled

23222 3224 OCOKCOKOairexhaled

The peroxide anion reacts with water to from hydrogen peroxide and hydroxide anions.

22222 22 OHNaOHOHONa

3. Reactions of the Alkali Metals with hydrogen

The alkali metals react directly with hydrogen at high temperatures to form hydrides.

LiHHLiot 22 2

NaHHNaot 22 2

The alkali metals hydrides are ionic compounds.

These Hydrides react with water to release hydrogen gas.

22 HLiOHOHLiH

22 HNaOHOHNaH

4. Reactions of the Alkali Metals with halogens

The alkali metals reduce halogens to form ionic halides:

NaClClNa 22 2

KIIK 22 2

KClClK 22 2

5. Reactions of the Alkali Metals with nitrogen

Lithium is the only element that reacts directly with nitrogen at room temperature:

nitridelithium

NLiNLi 32 26

The reddish black lithium nitride reacts directly with water to form ammonia:

ammonia

NHLiOHOHNLi 323 33

Compounds of alkali metals are for the most part white, high-melting ionic solids. With very few exceptions, alkali metal salts are soluble in water and the resulting solutions conduct an electric current, as a result of the dissociation of the salt into ions.

Not all the properties of lithium are analogous to those of the other members of the alkali metal family. For example, in contrast to the analogous salt of the other alkali metals, LiF and Li2CO3 are insoluble in water and LiCl is soluble in alcohols and ethers. The anomalous behavior of lithium is ascribed to the much smaller size of the Li+ ion.

Important Compounds of the Alkali Metals

1. Lithium chloride and lithium bromide, LiCl and LiBr. Because the Li+ ion is so small, Li salts have a affinity for H2O and yet a positive heat of solution, so they are used in dehumidifiers and air-cooling units. 2. Lithium carbonate, Li2CO3. Used to make porcelain enamels and toughened glasses and as a drug in the treatment of manic-depressive disorders. 3 Potassium nitrate, KNO3. Powerful oxidizing agent used in gunpowder and fireworks.

4. Sodium chloride, NaCl. Millions of tons used in the industrial production of Na, NaOH, Na2CO3/NaHCO3, Na2SO4, HCl, and purified for use as table salt. 5. Sodium carbonate and sodium bicarbonate, Na2CO3 and NaHCO3. Carbonate used as an industrial base and to make glass. Bicarbonate, which releases CO2 at low temperatures (500 to 1000), used in baking powder and in fire extinguishers. 6. Sodium hydroxide, NaOH. Most important industrial base; used to make bleach, sodium phosphates, and alcohols.

Biological importance of sodium and potassium

A typical 70 kg man contains 90 g sodium and 170 g potassium. This two alkali metals play a vital role in biological system. Sodium is major cation in blood plasma of vertebrates and potassium is a major cation in cytoplasm.

Flame test

The alkaline earth metals are metallic elements in the Group IIA in the periodic table. The alkaline earth metals are named after their oxides, the alkaline earths, whose old-fashioned names were beryllia, magnesia, lime, strontia and baryta. These oxides are basic (alkaline) when combined with water.

They are shiny silvery-white They readily lose their two outermost electrons to form cations with a 2+ charge They have low densities low melting points low boiling points, however…..

Physical properties of the alkaline-earth metals

Alkaline earth metals have higher density, higher melting point, higher boiling point, have less electropositive character than alkali metals.

Physical properties of the alkaline earth metals

The atomic and ionic radii of the alkaline earth elements are smaller than those of the corresponding alkali metals of the same period. This is due to increase in atomic number as well as increased nuclear charge in these elements.

The reactivity of the alkaline earth metals increase going down the group. Because the first ionization energy of the alkaline earth metals decreases down the group, it is easier for the outermost electrons to be removed from the atom and participate in chemical reaction, thus increasing reactivity down the group.

Occurrence of alkaline earth metals •All the discovered alkaline earth metals occur in nature. •Alkaline earth metals are obtained in the form of their ore in earth's crust. • Of the alkaline earth metals calcium and magnesium rank fifth and sixth in abundance respectively, in earth crust. • Beryllium is rare and radium is rarest of all.

Chemical properties of the alkaline earth metals

All the alkaline earth metals are highly reactive as they have tendency to lose 2 electrons from s-

orbitals.

Alkaline earth metals are less reactive than alkali metals. Alkaline earth metals the second most active

metals in the periodic system.

1. Reactions of the Alkaline earth Metals with water

They react with water to evolve hydrogen gas. The chemical reactivity of metal with water increase as we move from Mg to Ba. Be and Mg form an adherent oxide coating that allows only slight reaction.

222 )(2 HOHCaOHCa

222 )(2 HOHBaOHBa

Calcium metal reacting with water to form bubbles of hydrogen gas.

Hydroxides of alkaline earth metal Alkaline earth metals have tendency to form hydroxides. All the hydroxides are basic in nature and the basic strength increases on moving down the group.

All the elements of group 2 burns with oxygen gas to produce metallic oxide. The oxides of alkaline earth metals are less basic. Oxides become more basic on increase in electropositive character.

2. Reactions of the Alkaline earth Metals with oxygen

CaOOCa 22 2

BaOOBa 22 2

MgOOMg 22 2

Oxides can react with water to form hydroxides

22 )(OHCaOHCaO

All the alkaline earth metals combine with halogen at high temperature forming their halides.

3. Reactions of the Alkaline earth Metals with halides

22 CaClClCa

22 CaBrBrCa

22 BaClClBa

All the alkaline earth metals except Be, combine with hydrogen directly on heating to form metal hydride of general formula MH2.

4. Reactions of the Alkaline earth Metals with hydrogen

22 BaHHBa

22 CaHHCa

Alkaline earth metals react with acids liberating hydrogen.

5. Reactions of the Alkaline earth Metals with acids

222 HCaClHClCa

2442 HBaSOSOHBa

6. Reactions of the Alkaline earth Metals with nitrogen

2323 NCaNCa

2323 NBaNBa

Except Be

Important Compounds of the Alkaline Earth Metals

1. Beryl, Be3Al2Si6O18. Beryl occurs as a gemstone with a variety of colors. It is chemically identical to emerald, except for the trace of Cr+3 that gives emerald its green color. Beryl is the industrial source of Be metal. 2. Magnesium oxide, MgO. Because of its high melting point (28520C), it is used as a refractory material for furnace brick and wire insulation. 3. Calcium carbonate, CaCO3. Occurs as enormous natural deposits of limestone, marble, chalk and coral. Used as a building material, to make lime, and, in high purity, as toothpaste abrasive and antacid.

Biological importance of magnesium and calcium

An adult contains 25 g of Mg and 1200 g of Ca. The main pigment for the absorption of light in plants is chlorophyll which contains megnesium. Maximum percentage of calcium is present in bones and teeth.

Biological Role and Toxicity of Alkaline Earth Metals

Magnesium and calcium are essential to all known living organisms. They are involved in more than one role. For example, magnesium or calcium ion pumps play a role in some cellular processes. Magnesium functions as the active center in some enzymes, and calcium salts take a structural role in bones. Strontium plays an important role in marine aquatic life, especially hard corals, which use strontium to build their exoskeletons. Strontium and barium have some uses in medicine. For example "barium meals" are used in radiographic imaging, while strontium compounds are employed in some toothpastes. However, beryllium and radium are toxic. Beryllium's low aqueous solubility means it is rarely available to biological systems. It has no known role in living organisms, and, when encountered by them, is usually highly toxic. Radium has a low availability and is highly radioactive, making it toxic to life.