Consider a molecule composed of one hydrogen atom and one fluorine atom:. Each atom needs one additional electron to complete its valence shell. By each contributing one electron, they make the following molecule:.
In this molecule, the hydrogen atom does not have nonbonding electrons, while the fluorine atom has six nonbonding electrons three lone electron pairs. The circles show how the valence electron shells are filled for both atoms. When two chlorine atoms form a chlorine molecule, they share one pair of electrons.
In Cl 2 molecule, each chlorine atom is surrounded by an octet number of electrons. The Lewis diagram for a Cl 2 molecule is similar to the one for F 2 shown above. When a hydrogen atom and a bromine atom form HBr, they share one pair of electrons.
In the HBr molecule, H achieves a full valence of two electrons duet while Br achieves an octet. The formation of a water molecule from two hydrogen atoms and an oxygen atom can be illustrated using Lewis dot symbols shown below. The structure on the right is the Lewis electron structure , or Lewis structure , for H 2 O. With two bonding pairs and two lone pairs, the oxygen atom has now completed its octet.
Moreover, by sharing a bonding pair with oxygen, each hydrogen atom now has a full valence shell of two electrons. Chemists usually indicate a bonding pair by a single line, as shown below. Other large molecules are constructed in a similar fashion, with some atoms participating in more than one covalent bond. Again, sharing electrons between C and H atoms results in C achieving and octet while H achieving a duet number of electrons.
The number of bonds that an atom can form can often be predicted from the number of electrons needed to reach an octet eight valence electrons. In the Lewis structure, the number of bonds formed by an element in a neutral compound is the same as the number of unpaired electrons it must share with other atoms to complete its octet of electrons.
For example, each atom of a group 4A 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach an octet. These four electrons can be gained by forming four covalent bonds , as illustrated here for carbon in CH 4 methane. Group 5A 15 elements such as nitrogen have five valence electrons in the atomic Lewis symbol: one lone pair and three unpaired electrons.
To obtain an octet, these atoms form three covalent bonds , as in NH 3 ammonia. Oxygen and other atoms in group 6A 16 obtain an octet by forming two covalent bonds. Fluorine and the other halogens in group 7A 17 have seven valence electrons and can obtain an octet by forming one covalent bond. Typically, the atoms of group 4A form 4 covalent bonds; group 5A form 3 bonds; group 6A form 2 bonds; and group 7A form one bond. The number of electrons required to obtain an octet determines the number of covalent bonds an atom can form.
This is summarized in the table below. In each case, the sum of the number of bonds and the number of lone pairs is 4, which is equivalent to eight octet electrons.
Because hydrogen only needs two electrons to fill its valence shell, it follows the duet rule. It is an exception to the octet rule. Out of these 35 electrons, 7 will be located on the outermost shell , and thus be valence electrons. Now, atoms tend to unstable with outermost shells that have fewer than 8 electrons - this is known as an incomplete octet - so their chemical reactivity will depend on how close to having 8 electrons on their outemost shells are.
In bromine's case, it only lacks 1 electron to have a complete octet , so it will ty vigurously to get that one electron. To do that, a bromine atom forms a covalent bond with another bromine atom. Each atom contributes one electron to the bond, and share these bonding electrons equally.
The interesting thing about bromine is that it is actually a liquid at room temperature. The image intends to reflect the rich colour, liquidity and aromatic nature of the element. Bromine is a deep-red, oily liquid with a sharp smell. It is toxic. Bromine is used in many areas such as agricultural chemicals, dyestuffs, insecticides, pharmaceuticals and chemical intermediates.
Some uses are being phased out for environmental reasons, but new uses continue to be found. Bromine compounds can be used as flame retardants. They are added to furniture foam, plastic casings for electronics and textiles to make them less flammable. However, the use of bromine as a flame retardant has been phased out in the USA because of toxicity concerns.
Organobromides are used in halon fire extinguishers that are used to fight fires in places like museums, aeroplanes and tanks. Silver bromide is a chemical used in film photography. Before leaded fuels were phased out, bromine was used to prepare 1,2-di-bromoethane, which was an anti-knock agent.
Biological role. Bromine is present in small amounts, as bromide, in all living things. However, it has no known biological role in humans. Bromine has an irritating effect on the eyes and throat, and produces painful sores when in contact with the skin. Natural abundance. Bromine is extracted by electrolysis from natural bromine-rich brine deposits in the USA, Israel and China.
It was the first element to be extracted from seawater, but this is now only economically viable at the Dead Sea, Israel, which is particularly rich in bromide up to 0. Help text not available for this section currently. Elements and Periodic Table History. He took the concentrated residue which remained after most of the brine had evaporated and passed chlorine gas into it.
In so doing he liberated an orange-red liquid which he deduced was a new element. He was asked to produce more of it, and while he was doing so Balard published his results and so became known at its discoverer. Atomic data. Bond enthalpies. Glossary Common oxidation states The oxidation state of an atom is a measure of the degree of oxidation of an atom. Oxidation states and isotopes. Glossary Data for this section been provided by the British Geological Survey.
Relative supply risk An integrated supply risk index from 1 very low risk to 10 very high risk. Recycling rate The percentage of a commodity which is recycled.
Substitutability The availability of suitable substitutes for a given commodity. Reserve distribution The percentage of the world reserves located in the country with the largest reserves. Political stability of top producer A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators. Political stability of top reserve holder A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.
Supply risk. Relative supply risk 7 Crustal abundance ppm 0. Young's modulus A measure of the stiffness of a substance. Shear modulus A measure of how difficult it is to deform a material. Bulk modulus A measure of how difficult it is to compress a substance. Vapour pressure A measure of the propensity of a substance to evaporate. Pressure and temperature data — advanced. Listen to Bromine Podcast Transcript :. You're listening to Chemistry in its element brought to you by Chemistry World , the magazine of the Royal Society of Chemistry.
Hello, welcome to Chemistry in its element where this week we're sniffing out the chemical that is named after the Greek word for stench and this substance has certainly kicked up a stink in its own right in its time because it makes holes in the ozone layer. But it's not all bad as it's also given us drugs, insecticides and fire extinguishers and to tell the story of element number 35, here's chemist and author John Emsley.
Fifty years ago bromine was produced on a massive scale and turned into lots of useful compounds. Photography relied on the light-sensitivity of silver bromide, doctors prescribed potassium bromide as a tranquiliser, leaded petrol needed dibromomethane to ensure the lead was removed via the exhaust gases, bromomethane was widely used to fumigate soil and storage facilities, and fire extinguishers contained volatile organobromine compounds.
Today these uses have all but disappeared. World production of liquid bromine once exceeded , tonnes per year, of which a significant part was produced by a plant on the coast of Anglesey in Wales, which closed in This extracted the element from sea water, which contains 65 p.
He found that the salt residues left by evaporating brine from Montpellier, France, gave an oily red liquid when treated with acid. He realised this was a new element and reported it to the French Academy, who confirmed his discovery.
When they realised it was chemically similar to chlorine and iodine they proposed the name bromine, based on the Greek word bromos meaning stench. While some uses of bromine have declined because the products made from it are no longer needed, others have been discouraged because of the damage this element could cause to the ozone layer.
Volatile organobromine compounds are capable of surviving in the atmosphere long enough to reach the upper ozone layer where their bromine atoms are 50 times more damaging than the chlorine atoms - which are the main threat, coming as they did from the widely used chlorofluorocarbons, the CFCs.
The Montreal Protocol which outlawed the CFCs sought also to ban the use of all volatile organobromines by , and this restriction especially applied to the fumigant bromomethane and compounds such as CBrClF 2 which were in fire extinguishers for electrical fires or those in confined spaces.
Bromomethane was a particular cause for concern but banning it has proved impossible because it has some uses for which alternatives have not been found. Often referred to as methyl bromide, CH 3 Br boiling point 3. When figuring out whether to place a double or triple bond you should always look at the number of valence electrons present as well as the number of bonds a central atom is likely to form.
Another good way to know whether to use double or single bonds is to calculate the formal charge on each atom in the molecule. The number of bonds for a neutral atom is equal to the number of electrons in the full valence shell 2 or 8 electrons minus the number of valence electrons. This method works because each covalent bond that an atom forms adds another electron to an atoms valence shell without changing its charge.
The number refers to the number of bonds each of the element makes: Hydrogen makes 1 bond, Oxygen makes 2 bonds, Nitrogen makes 3 bonds and Carbon makes 4 bonds. A single lone pair can be found with atoms in the nitrogen group such as nitrogen in ammonia, two lone pairs can be found with atoms in the chalcogen group such as oxygen in water and the halogens can carry three lone pairs such as in hydrogen chloride.
Bromine will normally form one covalent bond. Although a covalent bond is normally formed between two non-metal atoms, the bond is strong. When two atoms bond together, they form a molecule. A bromine molecule is called a diatomic molecule since it has only two atoms. Hydrogen needs only two electrons to fill its valence, which it gets through the covalent bond.
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