Atoms combine to form molecule through chemical bonds. Same type of atoms combines to form molecules whereas different types of atoms combine to form compounds. For example; chlorine molecule is composed of two chlorine atoms whereas combination of two hydrogen atoms with one oxygen atom form water; a compound. The chemical bond is sharing or transfer of electron between bonded atoms.
On the basis of sharing and transfer of electrons; chemical bonds can be classified as ionic bond and covalent bond. Ionic bonds are formed by transfer of electrons between bonded atoms that results the formation of cation and anion which are bonded through electrostatic force of attraction. Unlike ionic bonding, covalent bonds are formed by equal sharing of electrons between bonded atoms. Different atoms form different types of chemical bonds which depend on their electronic configurations. Usually metals involve in ionic bonding as they have tendency to lose electrons to get the octet configuration. On the contrary, non-metals form covalent compounds by sharing of electrons. The bonding between metals and non-metals is ionic bonding in which metal exists as metal cation and non-metal as anion.
As we move from left to right across the period, the electronegativity of elements increases. In other words the elements at the left side are electropositive elements (metals) whereas elements at the right side are electronegative elements (non-metals). The elements of group-17 are most electronegative element commonly called as halogens. The elements of group-18 are called as Noble gases as they are least reactive or inert gaseous elements with octet configuration.
Halogens have seven valence electrons and require one more electron to get the octet configuration therefore they tend to form halides which are negatively charged anions with -1 charge. They can form ionic as well as covalent compounds. In this article we will discuss about chemical and physical properties of one of the halogen known as bromine.
Bromine is third element of halogen family placed in 17th group 4th period of periodic table. It comes after fluorine and chlorine so we can say that it is bigger in size compare to fluorine and chlorine but less electronegative compare o fluorine. This is because as we move down in a group the number of shell increases that increase the atomic radii but at the same time it also increases the distance between nucleus and valence electrons that decreases the ionization energy and electronegativity of elements. All halogens have 7 valence electrons and form halide ion with -1 charge like bromide ion is Br-. Like other halogens, bromine is also found as its salt with alkali metals such as sodium bromide, potassium bromide etc. Because of reactive nature bromine never found in free-state and always exist as a part of some salt or compound.
The electronic configuration of Br is [Ar] 3d10 4s2 4p5 with 35 atomic number and 79.90 is mass number. The valence shell configuration of bromine is 4s2 4p5. We know that bromine gas is a reddish brown gas with irritating odor. Even the word bromine is originated from word âbromosâ means smell bad. It was discovered by Antoine-JÃ©rÃ´me Balard in 1826 as one of the non-metallic element which can exist in liquid state at room temperature.
Bromine is a non-metal, part of halogen family with atomic number 35 and atomic mass 79.90 amu. The melting point of bromine is -7.2 °C and boiling point is 58.78 °C. The density of bromine is 3.1028 g / cm3. Like other halogens, bromine also exists as bromine molecule (Br2). It is a reddish brown gas which can exist as liquid at 20°C.
Bromine is mainly extracted by electrolysis from bromine-rich brine such as sodium bromide. Sea water is also used to extract this halogen. Compare to fluorine the electron affinity of bromine is less around 324.537 kJ/mol and electronegativity is 2.96.Different ionization energy values are listed below.
It is a deep-red, oily liquid with a pungent odor. It is toxic and hazardous liquid. Still it is a very useful halogen and involve in many fields such as manufacturing of insecticides, pharmaceuticals, dyestuffs, agricultural chemicals and different chemical intermediates. Usually compounds of bromine are flame retardants and are added to furniture foam, plastic casings and textiles to make them less flammable although this use is very limited due to toxic nature of bromine. Many organic bromides are used in halon fire extinguishers. These extinguishers are used to fight fires in museums, aero planes and tanks. Another use of bromide salt is in photography in the form of silver bromide. The exposure of bromine can cause irritation on the eyes and throat. It also causes painful sores on skin. There are various sources of bromine in nature.
- Seawater: Sea water is the best source of NaCl and NaBr.
- Pesticides: Bromine is one of the major ingredients of many pesticides and used to control insect infestations due to toxic nature.
- Plastics: Bromine is part of flame resistant plastics.
- Water purification: It is also used to disinfect the fresh water.
- Manufacturing of medicines: The great tendency of bromine to form different compounds makes it useful in the manufacturing of many useful drugs.
- Photography: Bromine salts such as silver bromide are used to develop the photographs.
There are mainly two stable isotopes of bromine atom. These isotopes are 79Br and 81Br, although 30 other radioisotopes are also known for same element. Out of those radioisotopes; 77Br is most stable with a half-life of 57.036 hours. From five halogen atoms, only bromine and chlorine have more than one stable isotope. The relative abundance of 79Br is 51 % whereas 81Br is little less close to 49 %. The atomic mass of 79Br is 78.918 amu and 80.916 amu for 81Br isotope.
Bromine is one of the most colorful halogen which exists as reddish brown liquid or gas. It is the only non-metal can exist in liquid state. Two scientists (Carl Lowig's and Balard) worked parallel on this element and identified it as a halogen. Due to high reactivity, it does not occur naturally on Earth as an element but many known compounds are found in Earth’s crust. It is 64th most common element on Earth and easily soluble so it is also found in sea water. Mainly bromine is produced from brine (a saturated solution of bromide salt). The diatomic molecule of bromine is Br2; also known as bromine gas. It is transparent, dark, reddish gas which can evaporate easily under normal conditions. It can react easily with metals to form metal bromides. Initially it used to replace iodine vapor as it is more reactive than iodine.
Later bromine compounds were also used as sedatives, seizure medications and as a poison gas in World War I era. Today it is one of the most important compound and part of many organic and inorganic synthesis processes.