Electronegativity is a measure of the relative tendency of an atom to attract a shared pair of electrons in a covalent bond. Fluorine the most electronegative element is assigned a value of 3. It means that when in a covalent bond with sulphur, oxygen will attract electrons towards itself more than sulphur.
It will gain a partial negative charge. When the atomic number increases, the number of electrons also increases to maintain the neutrality of the atom. For instance, if the K-shell holds 2 electrons, addition of 1 electron will result in addition of another energy level i.
This would happen only when at least 8 more electrons are added. In general,. Figure 4: Effective nuclear charge across some elements in Period 3 of the Periodic Table. Clearly, the effective nuclear charge increases across a period, in this case period 3. Due to this, the atomic size decreases. But down a group in a periodic table, the effective nuclear charge nearly remains the same.
However, addition of a shell every time, results in an increase in the atomic radius. Hence, in general, as elements get bigger, the effective nuclear charge on the valence electrons decreases due to the shielding provided by the inner shell electrons.
So the valence electrons can move around more freely. This statement is further explained in the discussions on polarisability and catenation in the article. Since oxygen has a smaller atomic size, in the case of the formation of single-bonded oxygen molecules, there are more interelectronic repulsions because there are more lone pairs of electrons.
Hence, di-atomic oxygen in which atoms of oxygen share two pairs of electrons i. But in the case of single sulphur bonds, the repulsions between the lone pairs of electrons are not very high as the size has increased.
Bond Energy is a measure of the strength of a chemical bond which is determined by measuring the heat or enthalpy required to break a mole of molecules into their constituent individual atoms. But a single bond between the two sulphur atoms does not satisfy valency of both the atoms. Hence, a longer chain of sulphur atoms is formed and sulphur has much more tendency to catenate [3] compared to oxygen. Carbon has an electronegativity of 2.
But their atomic size and valency differ. Carbon is much smaller and has only 4 valence electrons. Both these factors of size and tetravalency enable carbon to exhibit the highest degree of catenation. This makes long chains of carbon very stable. Hence, sulphur chains are much smaller as compared to carbon, to maintain stability.
For example, at At very high temperatures, the sulphur chains break to form smaller molecules like S 2 which happens to be the predominant in that condition. So we can see that the environmental conditions highly influence the bond formation of elements. Figure 5: Transition of sulphur from the rhombic form to the monocyclic form source:thechemistrysite. Covalent bonds are formed between atoms of elements having very small or no difference in their electronegativities, whereas ionic bonds are formed between atoms of elements with greater difference in their electronegativities.
Atoms of the same elements have the same electronegativities, therefore sulphur atoms are covalently, and not ionically, bonded electrons are shared to form sulphur molecules.
Figure 6: Electronegativity difference between bonding atoms source:chem. The reason is that, in such a case, the molecule is not polarised and has an overall uniform distribution of electrons between the constituent atoms. However, at times, instantaneous or momentary dipoles are formed. This happens due to the formation of an electron-dense region in one molecule which induces dipoles in other molecules.
These dipoles attract each other and the force between them is known as the London Dispersion Force. London Dispersion Forces are stronger in those molecules that are not compact, but longer chains of elements. This is an added factor in case of molecules like S8 which results in stronger bonds between them.
The Polarisability of a molecule can be defined as a measure of its ability to acquire an electrical dipole moment in response to an electrical field. The greater the distance of the electrons from the nucleus, the lesser the control of the nuclear charge on the electron distribution.
This allows for more distortions in the electron distribution or say, greater variability in electron density, and the polarisability of the atom increases. Note that since the constituent atoms are bigger, the molecule will also be bigger. Catenation is the self-linking ability of elements. Geoff Hutchison Lighthart Lighthart 6, 1 1 gold badge 17 17 silver badges 38 38 bronze badges.
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Linked 1. Can you think of why? What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent? Quote from: Corribus on December 01, , AM. N-N single bonds are also fairly unstable for a similar reason. On the other hand, S-S pi bonds are very unstable but the S-S single bond is reasonably stable. This explains why O does not form linear chains but S does.
This should tell you nicely why carbon sigma chains are ubiquitous, but nitrogen and oxygen chains are not. Now, the real question is: can you explain the explanation? Why are these bond energies as they are?
Quote from: Corribus on December 02, , AM. You've got two separate effects here you must explain. Let's condense the data. The characteristic clean odor associated with summer thunderstorms is due to the formation of small amounts of O 3.
Exposure to O 3 at higher concentrations leads to coughing, rapid beating of the heart, chest pain, and general body pain. At concentrations above 1 ppm, ozone is toxic. We can understand the importance of this filter if we think about what happens when radiation from the sun is absorbed by our skin. This electron eventually falls back into the orbital from which it was excited and energy is given off to the surrounding tissue in the form of heat. Anyone who has suffered from a sunburn can appreciate the painful consequences of excessive amounts of this radiation.
Radiation in the high-energy portion of the ultraviolet spectrum nm has a different effect when it is absorbed. This radiation carries enough energy to ionize atoms or molecules. The ions formed in these reactions have an odd number of electrons and are extremely reactive. They can cause permanent damage to the cell tissue and induce processes that eventually result in skin cancer. Relatively small amounts of this radiation can therefore have drastic effects on living tissue.
In Molina and Rowland pointed out that chlorofluorocarbons, such as CFCl 3 and CF 2 Cl 2 , which had been used as refrigerants and as propellants in aerosol cans, were beginning to accumulate in the atmosphere. In the stratosphere, at altitudes of 10 to 50 km above the earth's surface, chlorofluorocarbons decompose to form Cl atoms and chlorine oxides such as ClO when they absorb sunlight.
Cl atoms and ClO molecules have an odd number of electrons, as shown in the figure below. As a result, these substances are unusually reactive.
In the atmosphere, they react with ozone or with the oxygen atoms that are needed to form ozone. Molina and Rowland postulated that these substances would eventually deplete the ozone shield in the stratosphere, with dangerous implications for biological systems that would be exposed to increased levels of high-energy ultraviolet radiation.
Fluorine is the only element that is more electronegative than oxygen. As a result, oxygen gains electrons in virtually all its chemical reactions. Each O 2 molecule must gain four electrons to satisfy the octets of the two oxygen atoms without sharing electrons, as shown in the figure below. Oxygen therefore oxidizes metals to form salts in which the oxygen atoms are formally present as O 2- ions.
Oxygen also oxidizes nonmetals, such as carbon, to form covalent compounds in which the oxygen formally has an oxidation number of Oxygen is the perfect example of an oxidizing agent because it increases the oxidation state of almost any substance with which it reacts.
In the course of its reactions, oxygen is reduced. The substances it reacts with are therefore reducing agents. It takes four electrons to reduce an O 2 molecule to a pair of O 2- ions.
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