Ionic salts are characterized as compounds of highly electropositive metal ions (cations) such as sodium (Na+), potassium (K+), lithium (Li+), cesium (Cs+) or slightly less electropositive metal ions like calcium (Ca2+), magnesium (Mg2+), barium (Ba2+) with highly electronegative ions of nonmetals (anions) such as halides (X-: Cl-, B-, F-, I-), carbonates (CO32-), nitrates (NO3-), sulfates (SO42-) and phosphates (PO43-).

Ionic salts are compounds held together by ionic bonds due to characteristic state of existence of elements as cations and anions as well as energy stabilization of ionic compound known as lattice energy of formation. Ionic compounds liberate respective elements in their ionic state (cations & anions) on dissolving in water and other polar solvents. This character of ionic salts makes them useful compounds for enormous academic, pharmaceutical, medical and industrial applications. Their application is based on analytical chemistry of compound, titration characteristics, electrochemistry, ion-exchange chromatography and biochemical identification.

 Ionic salts most commonly exist as sea-salts or minerals present in the sea. Hydrosphere covers 80 per cent of earth’s surface in form of oceans, rivers, lakes, water basins and seas. There is a large number of elements present in seawater in form of dissolved salts. Salt-forming minerals known as halites easily dissolved in water.

Halites commonly occur as sedimentary evaporites from marine environment such as rock-salt or halite (NaCl), sylvite (KCl), and fluorite (CaF2). The main source of sea-salt is the chemical weathering of igneous rocks, which follows extraction of soluble salts with water. Igneous rocks and sedimentary rocks contain alumino-silicates of calcium, sodium and potassium that come in contact with rain water and ocean currents to dissolve soluble bicarbonate salts (HCO3-) of metal elements.

Bicarbonate ions react with K+ ions present in earth minerals and sand for form kaolin clay. Marine organisms can convert Ca2+ ions into CaCO3 (calcium carbonate shells), which can forms sediments. HCl injected by undersea volcanoes reacts with bicarbonates to liberate Cl- ions and CO2 in water. Therefore, seawater is rich in compounds of halogens, carbonates and sulphates. Salinity of rivers, lakes and oceans is due to presence of these dissolved metal salts like NaF, KCl, MgBr2, Mg(SO4)2, NaHCO3. Evaporation of water leads to dehydration of compounds that precipitate to form aggregates, which eventually settle in ocean beds or seabed.

Alkali salts are mainly dissolved sea-salts such as sodium chloride (NaCl), potassium chloride or syline (KCl), sodium carbonate (Na2CO3), sodium nitrate or chile salt petre (Na2NO3) formed from chemical weathering of sodium alumino silicate (NaAlSi3O8 – soda feldspar) and potassium alumino silicates (KAlSi3O3 - feldspar). Alkaline earth salts are slightly heavier and form insoluble salts expect halides and nitrates. Small size and bivalency of alkaline earth metal enables strong metallic bond formation, which imparts greater density, hardness and higher melting & boiling point temperatures. Some common sea mineral of alkaline salts are magnesite (MgCO3), dolomite (MgCO3.CaCO3), kieserite (MgSO4.H2O), gypsum (CaSO4.H2O), limestone (CaCO3), and barytine (BaSO4).

This section describes basic types of salts:
Halides or Halogen compounds: Alkali halides (MX) are very reactive binary compounds containing highly electronegative element halogen (X) with electropositive ion (M: Na, K). Heavy metal halides are considered as precursors for many halogen compounds. Alkali halides (NaCl, KCl) can be easily detected by reaction with silver nitrate (AgNO3) as they form distinct precipitate-salt with silver ions. Seaweeds (macro-algae) are considered as only natural source of organic halides in oceans and seas. Sodium and potassium salts are most common in biological fluids in tissues and body fluids that regulate buffering capacity of blood and transport of proteins and vitamins across cell membrane.

The most remarkable feature of cation gradient in cells is development of functional features such as nerve cells. In resting state, nerve cell exhibits electrical potential corresponding to potassium ion (K+) and sodium ion (Na+) concentration across membrane. The concentration ratio is 7:1 in red blood cells of humans and most mammals. This potential is discharged by release of acetylcholine during activation of nerve cells. The electrical discharge is transmitted as signal through the length of nerve cell by electrical impulse (signal transduction). Alkali hydrides are used as coolant in nuclear reactors. Sodium carbonate (Na2CO3) is commonly used reagent (detergent) for washing and softening of hard water. Baking soda is used as disinfectant, component of fire extinguisher and baking food. Alkali hydroxides are commonly used in industry to make soaps, mercerize cotton, laboratory reagent and preparation of other compounds such as explosives. Radioactive alkali like caesium and francium find uses in explosive

industry and nuclear medicine.
Carbonates: Carbonates are a polyatomic oxocarbon anion of general class (CO3)2- and bicarbonate (hydrogen carbonate or HCO3-) is intermediate anion. Carbonates are class of acidic oxide of carbon i.e. carbon-di-oxide (CO2) with additional oxygen atom. In fact, these exist in aqueous state as conjugated acid-base pair of intermediates in dynamic equilibrium, which consists of gaseous and dissolved CO2, carbonic acid (H2CO3), bicarbonate (HCO3)- and proton (H+), carbonate (CO3)2-  and diproton (2H+). Conjugated acid-base pair of carbonate salts and its derivates regulate aqueous buffer system inside living organisms. All metal carbonates are insoluble except carbonates of alkali metals like sodium carbonate (washing soda – Na2CO3) and potassium carbonate (potash – K2CO3). Biocarbonates of alkali and alkaline metals exhibit greater solubility, which is the principle constituent of hard water (presence of Ca2+ and Mg2+ ions). Carbonates cause effervescence by release of CO2 gas by heating at high temperatures (roasting) or reaction with dilute HCl.

Metal carbonates are used for conversion to corresponding metal halides and oxides. Carbonates of alkaline earth metals form insoluble aqueous precipitate (CaCO3, MgCO3, Fe2CO3). This is the main reason for their occurrence as clay salts in earth minerals. These are common constituents of cement and paint industry. Magnesium and calcium cations are vital for biological structure and functions in plants and animals. Magnesium is the main pigment for absorption of light by chlorophyll of plant leaves, which imparts it green color. Calcium ions and calcium phosphates occur as mineral deposit in bones, cartilages, tendons and ligaments of animals. These play important role in muscle contraction by binding to proteins and provide structural framework of body. Ca2+ & Mg2+ ions participate in vital enzyme reactions that control metabolism of body such as glycosis (hydrolysis), gluconeogenesis, amino acid metabolism and tricarboxylic acid cycle (TCA); and, metabolic energy transformations. Milk of magnesia and milk of lime is important pharmaceutical aid for gastric absorption of nutrients and digestion (antacids). These are also used in preparation of toothpastes, powders and food components. Barium is a radioactive element used in radiology studies in medical industry.

Nitrate and Ammonium salts: Nitrates (NO3-) and nitrites (NO2-) are group of conjugate bases that involves oxoanion of nitrogen in aqueous solution with its conjugate acid – nitric acid (HNO3). All inorganic nitrate and nitrite salts (metal nitrates) are soluble in water at standard temperature and pressure. These compounds are usually considered toxic in nature. Ammonia (NH3) is the natural precursor for nitrates and nitrites, which is either converted from atmospheric dinitrogen (N2) by nitrogen fixation process (nitrification) and decay of organic compounds containing nitrogen (amino acids, urea), known as ammonification (putrefaction). Ammonia and ammonium salts (NH4Cl) are naturally found in small quantities in rainwater, volcanic matter, and vegetative matter. Ammonium ions (NH4+) and quaternary ammonium salts (N4+) are released as by-product of animal metabolism in both terrestrial and marine environment (such as secretions of kidney). It is very soluble in water and catalyzes many important organic and inorganic reactions in plants and animals. Natural mineral deposits of nitrate salts are found in abundance on earth as nitratine (sodium nitrate – Na2NO3) and saltpeter (potassium nitrate - K2NO3). Nitrate mineral salts are used directly as component of fertilizers and fuel or used to obtain other organic and inorganic nitrates that find large number of commercial applications such as food preservation, curing, refrigerants, and nerve stimulants in medicinal formulations.

Phosphate salts: Phosphates are polyatomic oxoanion of phosphorus (PO4)3- that are insoluble in water under standard conditions except phosphate salts with alkali metal, ammonium and hydrogen. Phosphates are principle constituents of fossils and main inorganic mineral component of bones and teeth in vertebrates (calcium phosphate). In solid state, elevation of temperature results in condensation of phosphate units to form pyrophosphates (PPi or P2O74-) and polyphosphates (PnO3n+1(n+2)-). PPi or pyrophosphate is water-soluble under standard conditions and mainly responsible for biological catalysis (enzyme metabolism) for energy generation in vertebrate organisms. Phosphate-bound nucleic acids (ATP, GTP) and proteins regulate biological buffer (pH) and muscle energy through breaking of high-energy phosphate bonds (phosphagens). This is a common mechanism used by animal muscle tissues to regulate concentration of ATP for maintaining energy balance. Calcium hydroxyapatite precipitates along calcite in alluvial deposits of topsoil, plants and bacterial components (biominerals). Phosphates are often regarded as limiting nutrient in environment because they easily transform with other elements to form structural parts of living organisms. Phosphate salts determine the rate of growth of living organisms. Sodium salts of phosphates are important buffering agents and food preservatives.

Sulfate salts: Sulfate or Sulphate (SO4)2- salts are soft, fragile and possess some degree of transparency. Metal sulfates are formed by oxidation of sulfides (S22-) or treatment of metal oxide with sulphuric acid (H2SO4). Many metal sulfates are soluble in water and commonly formed out of sedimentary evaporites and hydrothermal veins containing sulphides. Gypsum (CaSO4) is most common anhydrous sulfate mineral containing calcium and component of plaster. Sulfate salts and acid derivatives are commonly important compounds used as surfactants or supplements.

Salts of Transition metals (heavy metals): These exist as mineral ores in form of their corresponding salts such as pyrites (FeS2, CuFeS2), cryolite (Na3AlF6), alums (double sulphate salts – potash alum, soda alum, chrome alum and ferric alums), siderite (FeCO3) and so on. Metal salts are commonly prepared by reacting their oxides or hydroxides with mineral acids, which find extensive use in catalysis and other application. Metal chlorides, nitrates and sulphates are soluble compounds whereas metal sulphides, carbonates and hydroxides form insoluble precipitate. Salts of heavy metals find common uses in making utensils, ornaments, mechanical parts like gears, tools, bearing, valves, bells, electrical applications (Cu, Ag), electroplating and electrotyping, explosive poisons and some other applications such as dying, tanning, medicine and inking.