Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: sorincosofret on 14/05/2008 05:29:34
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Covalent bound
Actual interpretation
Covalent bonds are formed as a result of the sharing of one or more electrons. In classical covalent bond, each atom donates half of the electrons to be shared. According to actual theories, this sharing of electrons is as a result of the electronegativity (electron attracting ability) of the bonded atoms. As long as the electronegativity difference is no greater than 1.7 the atoms can only share the bonding electrons.
Being in impossibility to explain coordinative complex and also the structure of a lot of common compounds, new theories about covalent bound were proposed. In the Valence Bond (VB) theory – one of must representative in quantum mechanic - an atom rearranges its atomic orbital prior to the bond formation. Instead of using the atomic orbital directly, mixtures of them (hybrids) are formed. This mixing process is termed hybridization and as result are obtained spatially-directed hybrid orbital.
An atom will adjust its hybridization in such a way as to form the strongest possible bonds and keep all its bonding and lone-pair electrons in as low-energy hybrids as possible, and as far from each other as possible (to minimize electron-electron repulsions).
In the simplest example hydrogen molecule formation, hdrogen atoms need two electrons in their outer level to reach the noble gas structure of helium. The covalent bond, formed by sharing one electron from every hydrogen atom, holds the two atoms together because the pair of electrons is attracted to both nuclei.
Proposed model of covalent bound
In proposed theory a covalent bound implies only a coupling of magnetic moments of individual atoms in order to obtain a greater stability. The electrons remain and orbit around proper nucleus, and consequently there is no sharing of electrons between atoms. When a covalent bound is broken the coupling between these magnetic moments is lost and of course every atom remains with his electrons. The situation is quite different in quantum theories, because when a covalent bond is broken the electrons are probabilistically distributed back to atoms so an electron form one atom can arrive to the other atom participating at bound. In proposed theory the electrostatic interaction between atoms participating at covalent bound formation is less important.
According to new interpretation, every atom of hydrogen possesses an electron magnetic moment due to the electron movement arround nucleus. The magnetic moment of nucleus is lower so it is not important in this case. The electron magnetic moment is formed by combination of orbital and spin magnetic moment using known rules of vectors and the orbital moment is greater then spin moment. The covalent bond means that both atoms attract reciprocally due to the magnetic interaction between their magnetic moments. The simplest interaction between two magnetic moments of different electron from different atoms is showed in down picture. The magnetic moments are pointed parallel but with opposite directions.
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Every atom has own electron and the electron orbit only around his nucleus and the orbits of electrons are situated in parallel planes . There is a dynamical equilibrium regarding a minimum distance between atoms, when the electrostatic repulsion force became stronger and a maximum distance between atoms when the coupling between magnetic moments force the atoms to move one to another. There is also an electrostatic push due to the electron reciprocal interaction and a nuclear push due to the nucleus reciprocal interaction. These interactions are smaller than magnetic interaction so the molecule is stable in normal condition.
The hydrogen molecules formed due to the opposite orientation of electrons magnetic moments has a lower energy comparative with the state of single atoms of hydrogen. The energy interaction between hydrogen atoms is given by:
W = -μ1B2cosθ1 -μ2B1cosθ2(1.1)
where μ1 and μ2 are electronic magnetic moments due to the different atom’s bound participant;
B1 represent the intensity of magnetic field created by μ1 at level of secondary atom orbit (r2) and B2 represent the intensity of magnetic field created by μ2 at level of first atom orbit (r1).
cos θ1 and cos θ2 represent the angle between μ1 and B2, respectively μ2 and B1 and due to the symmetry of hydrogen molecule θ1=θ2.
So in a first approximation, one electron is moving in the magnetic field created by the other electron from the other atom and reciprocally.
The orientation of B1 and B2 is antiparallel with orientation of μ1, respective μ2. This is due to the orientation of B tangent to the line of magnetic field created by μ1, respective μ2. In fig 3.2 is presented, as example, the magnetic moment produced by electron moving in the x-y plane with nucleus in the origin of system. The magnetic moment is along the z axis, the line of magnetic field go from North Pole and enter into the South Pole. The vector B is tangent to the magnetic line field, and at orbit electron plane and in other direction then N and S poles, B is antiparallel with m.
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Due to the orientation of electrons orbits, in case of covalent bound, the same antiparallel orientation is valid also for the μ1 and B2, respectively B1 and μ2.
The energy of magnetic interaction between two electrons gain a simpler expresion using a well known relation between the value of B created by a magnetic moment at distance r -see wikipedia:
The major and fundamental difference between quantum theory and proposed theory is that after forming of hydrogen molecules, every atom of hydrogen has only one electron around nucleus. The hydrogen atom doesn’t have a doublet structure according to new theory. There is no difference in atomic structure between atom of alone hydrogen atom and hydrogen atom in molecule. The only difference is the coupling of magnetic moment of hydrogen with another magnetic moment and this coupling insure a lower energy in case of molecule.
As comparison, quantum mechanic is incapable to explain why two opposite spin are lowering the energy of system. In the same time there is a contradiction in actual theory when the electrons are filled on subshell in atomic structure and when a covalent bound is formed. More precisely, the electrons fill a subshell first with one electron in every orbital with parallel spins and after that the existing electrons complete the orbital occupation with opposite electron spin. So if the coupled spin state is more stable, at occupation of subshell should be occupied complete an orbital and after hat another orbital.
For other elements, when we have a single electron in the last shell the situation is simple because for the inner shells, magnetic moments suffer an internal compensation. What’s happened when we have more electrons on the last shell?
Normally in the ground state electrons form pairs with opposite spin in order to maintain a low level of energy. But at interaction with other reactants a process of decoupling of pairs of electrons can happened. Depending on the condition of reaction, on the structure of element, on the stability of formed compound it is possible to have a partial decoupling or a total decoupling of electrons from last shell. As example: chloride having 7 electrons on the last shell, can participate:
• with one electron in chemical combination like in ground state,
• with 3 electrons, that means a decoupling of one pair of electrons plus the initial decoupled electron;
• with 5 electrons, that means a decoupling of two pairs of electrons plus the initial decoupled electron;
• with 7 electrons, that means a decoupling of three pairs of electrons plus the initial decoupled electron.
When a single electron on the last shell is presented and we have a single element bound, the orientation of electron magnetic moment is not so important. Of course the molecule formed is linear. When the number of electron magnetic moments is greater, the situation it is a little bit complicated but solvable and easy to understand. The magnetic moments of electrons are treated classical this means, the energy is minimum when the spread of magnetic moment is maximum. As consequence the magnetic moments, and of course the formed bounds, will have such orientation in order to insure a minimum interaction.
In case of two electrons on the last shell, this means two magnetic moments, and consequently two covalent bounds, the molecule is linear, the angle between bounds is 180º in case of two simple bound.
In case of three magnetic moments (three covalent simple bounds) a trigonal planar arrangement is preferred or a pyramidal trigonal structure in case of central atom with one lonely electron pair.
In case of four magnetic moments (four covalent simple bounds) the molecule will have a tetrahedral arrangement.
For five and six magnetic moment (five or six simple covalent bounds), a trigonal bipyramid and an octahedral structure are preferred.
In case of seven magnetic moments, due to the sterical interaction, it is imperative that minimum one covalent bound to be double due to the geometry of molecules.
Chloride with his electron structure can form up to seven covalent bounds. Don’t be scared with counting of number of electrons around chloride nucleus. Even we have seven covalent bound we will have only seven electrons on the last shell. But, sometimes the structure forms needs the necessity of an eighth bound, and in this case chloride catches another electron, and will form eight covalent bounds. We will see this situation for example at anion perchlorat structure.
This is the situation when only simple bounds are formed between atoms. But what is possible to predict using our model when a double or triple bond is formed?
In order to have a single bound between atoms we have seen that magnetic moments are opposite and situated on the line which unify both nucleus. A double bound have to respect the same condition: magnetic moment need be opposite in order to insure a lower energy for system.
Let’s take carbon as example with four magnetic moments. In order to form a first bound we must have fulfilled the condition that every atom comes with two electrons magnetic moments opposite orientated. For a simpler visual representation the first bound will be represented along the line which passes through both nuclei, even in reality the magnetic moments are a little bit shifted from this perfect alignment. In fig. 10 the simple bound is represented by magnetic moments noted with μ1x. For the second bound (called pi bound in quantum mechanic) in order to have an opposite orientation of magnetic moments, these must be orientated after z or y axes (in fig. 3.3 μ2z is after z axis). The minimum energy is attaint when the two magnetic moments participating at the second bound are in the same plane, so the first and second bound between carbon atoms delimitate a plane in our case x-z plane.
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Figure 3.3 Double bound formations
In order to have minimum energy perturbations the other two magnetic moments of every atoms of carbon, which will form other sigma bounds must be situated in x-z plane but directed to exterior. Practically, the magnetic moments of every atoms of carbon design a regulated triangular pyramid, one top orientated and another down orientated. Consequently three magnetic moments are in the same plane and the angle between them is 120º. This observation will help in designing the shape of molecules.
The double covalent bound formation suppose an alignments of four magnetic moments, and this fact force the molecule to preserve a certain geometry; the rotation around double bound is impossible. The other magnetic moments (m3 and m4) in our example can form other two simple covalent bound and they are orientated in another plane perpendicular on the plane of formed bounds.
Some energy is spent for the alignments of second or third magnetic moments in case of double and triple covalent bound; it’s normally that energy of secondary bound is smaller in comparison with energy of first bond. And also the coupling is not so strong in case of two magnetic moments aligned on two parallel lines (case of pi bound) like in case of alignment on the same line (case of sigma bound).
The formation of triple covalent bond between two atoms implies that we have minimum three magnetic moments available; we will discuss for carbon which present four magnetic moments. The first two magnetic moments from every atoms form double bound as up described (μ1x form sigma bound and μ2z a pi bound). The third magnetic moment orbital found in plane x-y in case of double covalent bound, must be aligned after z axe (fig. 3.4) and will form a second pi bound. The fourth remaining orbital will be align in opposite with μ1x. Practically in case of a triple bond the distribution of magnetic moment is crossed, similar to ground state. The only difference is that in this case we have a coupling between electron magnetic moment from different atoms and not from the same atom like in ground state. If in ground state in case of carbon for the same atom μ1 is coupled with μ4 and μ2 with μ3 from the same atoms, in case of triple bound every of these magnetic moments are coupling with other magnetic moments form another atoms.
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Figure 3.4 Triple bound formation
For chosen example the magnetic moments μ4 remain free and can form another simple bound with other two atoms. In the case of a triple bound the molecule is linear due to the alignment of magnetic moments.
As we can see the difference between energetic of double bond or triple bond and energetic of similar number of single bonds is given by the orientation of magnetic moments during interaction and is not a different interaction. Consequently the energy of second bond (pi bound) interaction will differ as value regarding the first bound (sigma bound).
In case of different atoms which form a covalent bond, we will have the same coupling between magnetic moments of electrons participating at bond building. The magnetic moments of two electrons from two different elements will differ a little bit as absolute value. Consequently the opposite orientation of magnetic moments during bound formation leave the bound with a small magnetic moment uncompensated. In case of identical atoms the compensation is complete. Therefore some molecules possess a small remanent magnetic moment.
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Pleasse let me know what molecules have bonds in them that cannot be explained by current theories.
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The answer for your question is to long to be solved in few sentences.
The moderator of the forum banned me for advertising, so if you are really interested, a simple search on goggle will give you more detail about the topic.
Actual chemistry is not able to respond to give a simple interpretation of enthalpy released in a chemical reaction, neither to a chemical structure to a compound known maybe from antiquity.
Maybe you can help me and make clear how, according to mass energy equivalence, accepted by actual quantum chemistry, a part of reagent mass is transformed in energy? From where we chunk a part of mass to transform in energy? From electron or from nucleus? How appear a electron which change 0.001% from its mass in energy?
The fact that on basis of quantum mechanic a distribution of probability is counted for some chemical structure does not mean nothing for a logical mind.
Probability express our ignorance in face of a hidden causality said sometimes Einstein and in this point I support his affirmation.
At the end of the year a book related to chemistry principle will be available with a new interpretation for 90% of actual chemistry.
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Maybe I'm not reading far enough into the theory, but how does this explain conjugated systems, where electrons are shown to flow freely throughout the system???
For example benzene or 1,3-butadiene where the pi electrons are thought to be dispersed throughout the entire molecule. How does this theory explain aromaticity? Why is an aromatic compound lower in energy than a non-aromatic or anti-aromatic compound??
Also how can this "new theory" explain how these conjugated systems absorb specific wavelengths of the electromagnetic spectrum, if not by quantum mechanics???
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Dear Cut Chemist,
A book entitled Principles of Chemistry is in translation process and I hope until the end of the year will be available.
The benzene structure is not so complicated with a strange distribution of charge probability as is presented by quantum mechanic.
There are more texts available on my site, but it is necessary to search you after them because I'm banned to advertise here.
The explanation for new benzene structure:
Carbons participate at benzene structure with four unpaired magnetic moments produced by decoupling of double pairs of electrons in ground state. Every atom of carbon form with one hydrogen atom and two neighbor carbon atom three simple covalent bond due to the reciprocal compensation of magnetic moment on the line which join the nucleus. The remaining magnetic moment of carbon atoms is perpendicular on the plane of ring and is orientated alternately up and down like in fig. 3.5
In this case along entire benzene ring we have three up magnetic moment intercalate with three down magnetic moments. This extended magnetic interaction assure a great stability of nucleus. Each electron remains attached to his nucleus, and they are not spread along entire nucleus.
With 6 magnetic moments we must have normally 3 double bounds. But in reality every magnetic moments interact with left and right opposite neighbor magnetic moments, this interaction making the benzene ring more stable. Consequently we can speak not of delocalization of electrons in benzene ring, and also not a delocalization of magnetic moments. It is only an extended interaction which makes the system more stable.
The shape of benzene it is easily explained by the planar orientation of there magnetic moments. So between three neighbors C and between two C and Hydrogen we have an angle of 120º. The length of C-C bound is the same so we have a regular hexagon.
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The energetic stability of benzene is due to the extended interaction of magnetic moments because the energy necessary to destroy the coupling between six magnetic moments arranged in a ring is greater then the triple of a simple double bound. The chemical properties of benzene are a consequence of this ring stability.
Regarding the quantum hypothesis, I think the chemistry is not able to deal with this. Chemistry was not able to have a model for a chemical bound and it was served the food prepared by quantum mechanics.
There are some proposed experiments against quantum idea, but for chemistry forum it will be posted only how actual explanation for fluorescence and phosphorescence contradict quantum idea.
The texts are already available somewhere .. so if you are curious ... catch them before posting on nakedscientist.
regards,
Sorin
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"The answer for your question is to long to be solved in few sentences. "
No, its not.
My question was "Pleasse let me know what molecules have bonds in them that cannot be explained by current theories."
A perfectly acceptable answer would be the name of a molecule.
One word, the name, would do.
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Dear Bored chemist,
Take the ammonia and hydrochloric acid as example. When this substances are mixed nothing should be happen. Both substances are according to quantum mechanic in a maximum stability ( nitrogen, hydrogen and chloride all are with full layer of electrons). Why the reaction is spontaneous?
99% of coordinative complex does not respect the rule of octet. In fact except some simple example, the rule of octet is completely disrespected.
Let's consider a carbonate anion (known from antiquity).
The Lewis structure for this ion has a carbon-oxygen double bond, and two carbon-oxygen single bonds.
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Each of the singly bonded oxygen atoms bears a formal charge of minus one. These structures are similar in that the have the same types of bonds and electron positions, but they are not identical. The position of the carbon-oxygen double bond makes them different. In first structure the double bond is with the top oxygen atom, in second with the right hand oxygen atom, and third with the left hand oxygen atom. These oxygen atoms are at different places in space, so these are different structures.
All laboratory experiments have failed to detect these structure. Experimental measurement show that all three bounds are equals. In order to explain this, the resonance theory admit that these structure do not exist and the correct structure is given by a partial distribution of charge – a resonance structure type :
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The single pi bond in carbonate is now delocalized over all the atoms in the molecule, spreading out the negative charge, and stabilizing the molecule by reducing electron repulsion.
Did you asked how is possible from a mathematical distribution to accept a real charge fragmentation ?
How is possible to have a real resonant structure with charge of fraction of a fundamental charge?
In proposed structures there are not such abberations.
The structure of benzene was up presented so you can compare the actual quantum mechanic prediction with proposed one.
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"Did you asked how is possible from a mathematical distribution to accept a real charge fragmentation ? How is possible to have a real resonant structure with charge of fraction of a fundamental charge?."
Because it's an average over time.
On average I'm roughly 33% at work 10% out for a drink and 57% at home. But I'm always all of me in one place.
If you look at the electron density with something like electron difraction you get an average value over many molecules and a long time.
So I'm still waiting for you to tell me what use your theory is. What problems does it solve?
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B.C.,
You didn't answered at a simple question:
How is possible for the simple case of helium to have 2 electrons with the same energy (according to QM both are in the shell 1s) and to have so different energy of ionization?
How can you explain for Pb as example the same situation where the difference between 1s1 and 1s2 electron is more then 1000 eV?
An in all quantum mechanic texts the difference between 1s1 and 1s2 electron is given by its spin which has a value of h/2pi. Probably there is necessary to introduce a little bit more constants in order to explain this reality.
One of the use of proposed theory regard a logical explanation for this fact.
Another advantage regards the structure and spatial arrangement of molecules. To date there are a lot of theory and every theory explain a slice of these characteristics.
The book about a new perspective of chemistry is in translation so I can't say to much from it.
But I can give you as meditation theme a simple problem already solved, regarding the metallic bond.
According to actual conception, metallic bound is formed by sharing one or more electrons between a great number of atoms in the metallic network.
Accepting as correct the definition, for closed Z metals (as example Na, Mg, Al) it should exist a increased bound strength in connection with number of electrons shared.
This is true, if the enthalpy of melting or vaporisation are compared.
But in the same time the electric conductivity according to actual interpretation must be related to number of electrons shared. So it should be a increasing of metals conductibility when more electrons are shared. The evidence is contrary : for more electrons shared the conductibility is worse.
The most conductive metals are Ag, Au, Cu, which, according actual theory, participate with one electron ( 4s1 3d10 )at metallic network formation.
Think about it because in the proposed theory such correlations are piece of cake.
The proposed theory does not work with probability; the causality is introduced at atomic level. Of course nothing stop you to have a statistical description of a system. But the idea of entanglement and Heisenberg relations are ruled out.
Look at the post with ionization energy distribution and try to fit a d or f actual layer distribution with the measured one and you will see that represents time waste.
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"How is possible for the simple case of helium to have 2 electrons with the same energy (according to QM both are in the shell 1s) and to have so different energy of ionization?"
Easy- once you take the first electron out it stops screening the second one from the effect of the nucleus.
The conductivity of metals is a lot more complex than just counting the electrons, if it were that simple all conductors would be superconductors. What stops them being perfect conductors is a matter of solid state physics rather than chemistry but it includes things like grain boundaries.
I'm not going to spend my time looking up the physics of it for 2 reasons. Firstly it is simply a matter of looking up the answer in a textbook. The answer is already know so you could look it up just as easily as I could. Secondly I am not going to waste my time on your theory which predicts other things which are known to be wrong.
Speaking of not answering simple questions.
What molecules have bonds in them that can't be explained by current theories?
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Actual chemistry is not able to respond to give a simple interpretation of enthalpy released in a chemical reaction, neither to a chemical structure to a compound known maybe from antiquity.
Maybe you can help me and make clear how, according to mass energy equivalence, accepted by actual quantum chemistry, a part of reagent mass is transformed in energy? From where we chunk a part of mass to transform in energy? From electron or from nucleus? How appear a electron which change 0.001% from its mass in energy?
From the variation of the electromagnetic field.
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B.C,
I'm not interested to respond at your comments.
Please make a mental control learn, to speak polite, and after that maybe I will answer to you.
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Sorin,
People reading this will spot that my first question was perfectly polite.
They will also notice that you have not answered it.
They may come to their own conclusions about whether you "won't" answer it or you can't answer it.
I have come to thconclusion that you can't.
Feel free to prove me wrong.
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Sometimes I think that sorin has found the equivalent to the link below with Science phrases substituted for excuses. Just when you think you are on to something he changes direction and introduces a new diversion.
http://glossynews.com/funnyhitman/excuse.htm (http://glossynews.com/funnyhitman/excuse.htm)
I feel that would both struggle to pass the Turing Test.
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Sophie,
I think next week I will put a last thread regarding the mechanism of organic reaction in a new interpretation. Probably you think that my job is to answer from our to hour at any question made by a forum visitors. Most of the questions are not directly related to the subject of the thread but to other implication, so I'm not the principal actor of diversions.
As I told you, I have a job, I have to work at the basis of this theory, I have to care of my family and my garden and after that I read the messages (generally after midnight).
I think there are a lot of interesting threads on the forum and please read them until I will be able to post the new thread. If I wouldn't prepare my journey (about 2500 km) the thread were ready in this weekend.
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Sophie,
I think next week I will put a last thread regarding the mechanism of organic reaction in a new interpretation. Probably you think that my job is to answer from our to hour at any question made by a forum visitors. Most of the questions are not directly related to the subject of the thread but to other implication, so I'm not the principal actor of diversions.
As I told you, I have a job, I have to work at the basis of this theory, I have to care of my family and my garden and after that I read the messages (generally after midnight).
I think there are a lot of interesting threads on the forum and please read them until I will be able to post the new thread. If I wouldn't prepare my journey (about 2500 km) the thread were ready in this weekend.
What about working at the basis of physics? Or you're just aimed to get some money from a book of rubbish (counting on the hope that no much people is knowledged enough to understand it?)
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I do believe sorin regards himself as some kind of consultant.
Physician heal thyself, perhaps?
Probably you think that my job is to answer from our to hour at any question made by a forum visitors.
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Sorin,
You put forward a "theory" I pointed out that is, at best, redundant and therefore useless.
That's about as important a comment as anyone could make about it, yet you describe it as an irrelevance.
You have not even tried to give an answer to my question.
You may be busy but you have had nearly a month.
It's not as if I am asking for any complicated explanation.
All I asked for is the name of a compound for which the current theory does not offer an explanation of the bonding.
One word would do.
I will happily accept a CAS number if the translation of a chemical name into English troubles you.
Basically Sorin it's time to explain what good your "theory" is or shut up about it.