What Are Alkali Metals?
The alkali metals are six chemical elements in Group 1, the leftmost column in the periodic table. They are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). (Except hydrogen (H) has one electron in its outermost shell, but it is not classed as an alkali metal since it is not a metal but a gas at room temperature.)
The alkali metals are so named because when they react with water, they form alkalies. Alkalies are hydroxide compounds of these elements, such as sodium hydroxide and potassium hydroxide. Alkalies are very strong bases that are caustic. Lye, for example, is sodium hydroxide. Alkalies react with acids to form salts.
In their pure forms, alkali metals are soft, shiny metals with low melting points. Alkali metals react readily with air and moisture. Due to their reactivity, special precautions must be taken when using and storing these metals.
The alkali metals are highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen).
Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.
Alkali Metals on Periodic Table
The alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). This group lies in the s-block of the periodic table, as all alkali metals have their outermost electron in an s-orbital.
The alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting similar properties. For instance, when moving down the table, all known alkali metals show:
- Increasing atomic radius,
- Decreasing electronegativity
- Increasing reactivity
- Decreasing melting and boiling points
In general, their densities increase when moving down the table, with the exception of potassium, which is less dense than sodium.
Properties Of Alkali Metals
Alkali metals are a group of chemical elements in the periodic table with the following physical and chemical properties:
- Highly reactive at standard temperature and pressure
- Readily lose their outermost electron to form cations with a charge of +1
The alkali metals have low melting points. Lithium melts at 180.5 °C (356.9 °F); cesium melts at just 28.4 °C (83.1 °F). These elements are also excellent conductors of heat and electricity. The alkali metals are very reactive and so are usually found in compounds with other elements, such as salt (sodium chloride, NaCl) and potassium chloride (KCl).
They can all be cut easily with a plastic knife due to their softness, and their shiny surface tarnishes rapidly in the air due to oxidation. Because of their high reactivity, alkali metals must be stored under oil to prevent reaction with air.
In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, excluding hydrogen. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.
Properties of the alkali metals:
|Atomic weight (or stablest isotope)||6.941||22.99||38.098||86.468||132.905||223|
|Color of element||Silver||Silver||Silver||Silver||Silver||—|
|Melting point (°c)||180.5||97.72||63.38||39.31||28.44||27|
|Boiling point (°c)||1,342||883||759||688||671||677|
|Density at 20 °c (grams per cubic centimeter)||0.534||0.971||0.862||1.532||1.873||—|
|Volume increase on melting (percent)||1.51||2.63||2.81||2.54||2.66||—|
|Mass number of most common isotopes (terrestrial abundance, percent)||6 (7.59), 7 (92.41)||23 (100)||39 (93.2581), 40 (0.0117), 41 (6.7302)||85 (72.17), 87 (27.83)||133 (100)||—|
|Color imparted to the flame||Red||Yellow||Violet||Yellow Violet||Blue||—|
|Main spectral emission lines (wavelength, angstroms)||6,708; 6,104||5,890; 5,896||7,699; 7,665||4,216; 4,202||4,593; 4,555||—|
|The heat of fusion (calories per mole/kilojoules per mole)||720 (3)||621 (2.6)||557 (2.33)||523 (2.19)||500 (2.09)||500 (2)|
|Specific heat (joules per gram kelvin)||3.582||1.228||0.757||0.363||0.242||—|
|Electrical resistivity at 293–298 k (microhm centimeters)||9.5||4.9||7.5||13.3||21||—|
|Magnetic susceptibility (cgs units)||14.2 (10−6)||16 (10−6)||20.8 (10−6)||17 (10−6)||29 (10−6)||—|
|Crystal structure||Body-Centered Cubic||Body-Centered Cubic||Body-Centered Cubic||Body-Centered Cubic||Body-Centered Cubic||—|
|Radius: atomic (angstroms)||1.67||1.9||2.43||2.65||2.98||—|
|Radius: ionic (+1 ion, angstroms)||0.9||1.16||1.52||1.66||1.81||1.94|
|Radius: metallic (angstroms, 12-coordinate)||1.57||1.91||2.35||2.5||2.72||2.8|
|First ionization energy (kilojoules per mole)||520.2||495.8||418.8||403||375.7||380|
|Oxidation potential for oxidation from the 0 to +1 oxidation state at 25 °c (volts)||3.04||2.71||2.93||2.92||2.92||2.92|
List of Alkali Metals
The alkali metals are:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Cesium (Cs)
- Francium (Fr)
The International Union of Pure and Applied Chemistry (IUPAC) excludes hydrogen (H) as an alkali metal because it occurs as a gas under ordinary temperatures and pressures. However, hydrogen displays many of the properties associated with elements in the group and does become an alkali metal under extremely high pressure.
Examples Of Alkali Metals
The alkali metals are six chemical elements in Group 1, the leftmost column in the periodic table. They are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
Lithium is the lightest metal discovered yet. It is the only metal that reacts with nitrogen. Lithium Oxide is Amphoteric (both acid and base characteristics). Except for Lithium, other alkali elements are predominantly ionic. The charge density of Lithium is stronger than other alkali metals due to which it is extensively hydrated.
Lithium was discovered in 1817 by Johan Arfvedson, during petalite LiAlSi4O10 analysis. The word Lithium is derived from the Greek word ‘lithos’ meaning stone. Lithium is found in a number of pegmatitic minerals, clays, brines, oceans, and in all living things.
Uses of Lithium
- Lithium is used in heat-resistive ceramics and glasses.
- An alloy of Lithium is used in aircraft building.
- Lithium Deuteride is used as a fusion fuel in thermonuclear weapons.
- Lithium batteries are packed with a lot of energy as compared to other metals. Revolutionized devices like cell phones, and computers use lithium batteries.
- Lithium salts are used as a mood-stabilizing drug.
- Lithium-6 is the main source of tritium production.
- Lithium is used in deoxidizing copper and copper alloys.
- Lithium compounds are used as pyrotechnic colorants in fireworks that produce red luminance.
- Lubricating greases are produced from Lithium.
Sodium is a chemical substance that we consume every day in our food in the form of sodium chloride (common salt). Sodium is produced by the electrolysis of sodium chloride. The sodium element is highly reactive.
In 1806, Sir Humphry Davy, a chemist, obtained sodium by passing an electric current through molten sodium hydroxide. Sodium was first produced through nuclear fusion in stars, by the fusion of two carbon atoms. It can also be produced in stars when neon atoms gain a proton.
Uses of Sodium
- Sodium is used as luster in metals.
- Liquid Sodium is used as a coolant in nuclear reactors.
- The sodium salt of fatty acids is used in soap.
- NaK, an alloy of sodium and potassium, is an important heat transfer agent.
- Sodium compounds are used in paper, textile, petroleum, and chemical industries.
- Sodium Iodide is used to treat extensive ringworm.
- Sodium is used in street lights and sodium vapor lamps as it can give a yellow glow with bright luminance.
- Sodium hydroxide is used as oven cleaner.
Potassium is the 19th element in the periodic table. Potassium plays a vital role in the proper functioning of our bodies. It is an essential mineral that should be maintained in organisms. If the potassium level is not balanced it may lead to hyperkalemia or hypokalemia.
Potassium turns gray on exposure to air. To prevent oxidation and to keep out moisture, potassium is stored in petroleum.
Uses of Potassium
- Potassium chloride is essential for the growth of plants. It is used in fertilizers.
- Potash improves water retention, yield, nutrient value, taste, color, texture, and disease resistance of food crops.
- Potassium chlorate and potassium nitrate are used in explosives and fireworks.
- Potassium nitrate is used as a food preservative.
- Potassium maintains blood pressure and acidity levels in our bodies.
- Potassium chromate is used in the tanning of leather and in the manufacture of inks, gun powder, dyes, safety matches, etc.,
- Potassium is essential for normal cell respiration and electrolyte function as 95% of our cells are made of potassium.
- Potassium hydroxide is used to make detergents.
- Potassium helps to pump fluids inside the heart and the nerves.
Rubidium is a radioactive element. It is derived from the Latin word rubius meaning deepest red.
Uses of Rubidium
- Rubidium 82 is used in myocardial perfusion.
- Rubidium is used in the manufacture of atomic clocks, electronic tubes, and photocells.
- Rubidium is used as a working fluid in vapor turbines.
- It is used as a component in the engines of space vehicles.
- Rubidium vapor is used in laser cooling.
- Rubidium chloride is used to induce cells to take up DNA.
- It is used in thermoelectric generators.
- Rubidium Carbonate is used in making optical glasses.
- Due to the hyperfine structure of rubidium’s energy levels, it is used in atomic clocks.
- A compound made up of rubidium, silver and iodine has certain electrical characteristics and is used in making thin-film batteries.
Cesium is an active metal. Chemically, cesium is the most electropositive element and combines with anions to form compounds. It is a highly toxic element. Cesium hydroxide is the strongest base discovered yet.
It has many isotopes of which cesium-133 is a stable isotope and the most important standard for the measurement of time (Cesium clocks or atomic clocks). Cesium is liquid at or near room temperature.
Uses of Cesium
- Cesium-134 is used in the nuclear power industry.
- Used in photoelectric cells due to their quick electron emission.
- Cesium is used as a catalyst for the hydrogenation of certain organic compounds.
- It is used in propulsion systems.
- It removes air traces from vacuum tubes.
- Cesium is used in photovoltaic cells, television image devices, and night-vision equipment.
- Cesium vapor is used in the magnetometer.
- Cesium-137 is used in brachytherapy to treat cancers. (Brachytherapy is a cancer treatment method using radioactive elements)
- Cesium chloride solution is used in molecular biology for density gradient ultracentrifugation, primarily for the isolation of viral particles, subcellular organelles and fractions, and nucleic acids from biological samples.
- Cesium is used as a standard in spectrophotometry
- It is used in military aircraft.
Francium has the lowest electronegativity among all the known elements. It is a highly radioactive metal and the heaviest of these metals. Francium is produced by bombarding thorium with protons or by bombarding radium with neutrons.
This element is rare and is not used much. It is mainly used for scientific research in a laboratory. It decays quickly as it has a short half-life.
Alkali metals are of great use to us but should not be used without expert guidance as they get violent during reactions and should be handled cautiously as they are toxic.