Molecular Orbitals -- Shape and Symmetry? | Yahoo Answers
So long as the molecules are spaced sufficiently far apart. . The shape of the Universe will depend on the nature of the expansion; . Thus, the Universe, under this proposition, can be dated as to its age in years. .. taken as the distance from the Sun to the far orbital position of Pluto, or ~ x km). Main · Videos; Betel nut buyers in bangalore dating molecular orbitals shape and symmetry yahoo dating · over the phone dating sites · who dating website. Main · Videos; Courtship dating meaning crystal castles arcade symmetry yahoo dating molecular orbitals shape and symmetry yahoo dating maryborough .
Many scientists believe that what may have "existed" prior to the Universe was a quantum state in a sense, analogous to the condition of "potency" in ancient Greek philosophy which influenced a true vacuum no matter whatsoever that somehow possessed a high level of energy of unknown nature but not, however, as photon radiation.
What is the quantum theory explanation for transparency and opaqueness?
But, rarely, annihilation did not occur, so that a particle could grow and trigger a 'phase transition' that led to the singularity from whence all that entails the Universe - matter, energy, space, and time - came into being. In this quantum model, it is conceivable that many such singularities could form from time to time, leading to mulitple universes that, as far as we know theoretically, cannot have any direct contact. This is one example of prohibition by relativistic limits, in which information travelling at the speed of light cannot reach us from beyond the horizon - outer edge - of our own observable universe.
The concept of the Cosmological Horizon refers to the boundary or outer limits of the Universe that we can establish contact with. This is approximated by the currently observed farthest galaxies that formed in the first billion years of cosmic time. This Horizon is also conceptualized as the surface dividing spacetime which includes all locatable 4-dimensional points into what we can see and measure from what is hidden and unobservable.
The observable therefore must lie within our Light Cone, an imaginary surface that encloses all possible paths of light reaching us since the beginning of time.
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The second illustration below is an example. Check page for further discussion of these ideas. The controlling factor in this "visual" awareness is just the speed of light photons. We actually have detected cosmic background radiation [see page ], which pervades the entire Universe, whose first appearance was only aboutyears since the beginning of the B.
A distinction must be made between observed and observable: As time moves through the future, the horizon will move into ever more of the ultimate Universe. In the Standard Model for the Big Bang, there have been and are parts of the Universe which cannot directly influence each other because there hasn't been enough time for light from one part to have reached the other. Thus, the 'horizon' relative to Earth as the observing point but any other position in the Universe is equally as valid an observing point refers to the spatial or time limit that demarcates between what we can establish contact with in any part of the Universe and what lies beyond.
This figure illustrates an extreme example of parts that cannot mutually communicate: Let astronomers look out towards the apparent limits to the "outer" Universe, say at a distance of 13 billion light years, in two opposite directions. We, at the center of this diagram, would assume that the galaxies at the opposing edges are 26 billion light years apart. But for a 14 billion year old Universe, and radiation from each set of galaxies traveling at the speed of light, a signal from one galaxy group would not have had enough time to penetrate well beyond US into the region of space on the other side.
Thus, there is no time for communication between one part of the Universe and various other parts. This is true throughout a Universe whose dimensions are equivalent to a 28 billion light-year diameter sphere not necessarily the real shape of the Universe, but an adequate means to visualize the collection of objects in the observable part of the Universe. Within this sphere, there are pockets of space that are not in touch with other pockets. This seeming paradox is called the "Horizon problem".
This appears to violate the fundamental principle of universal causality, which holds that during expansion all parts of the Universe would need to have been in communication by light transfer or other means of exchanging energy so that the fundamental principles of physics would have ample causal opportunity to influence each other.
This is seemingly necessary if at a gross scale the Universe is to maintain uniformity the essence of the Cosmological Principle which postulates broad homogeneity and isotropism. One explanation that accounts for the causality needed to obey this Principle is given below in the subsection dealing with Inflation.
Nevertheless the isolation of regions of the Universe from one another is a real fact, as evident in the above illustration. And, specifically there were situations whereby some parts of the Universe were not in causal contact shortly after the Big Bang, and thus not visible to one another during early cosmic history, but will eventually as expansion proceeds become known to each other. Consider the diagram below: Silk, The Big Bang, 2nd Ed.
Reproduced by permission of W. Over expansion time, their light cones would eventually intersect, allowing each to see at time t1 other parts of the Universe in common but not yet one another. At a later time, beyond t2 "now" in the future, the horizons of A and B boundaries of the two light cones will finally intersect, allowing each to peer back into the past history of the other.
Commenting further on the Universe's geometry: One view holds the present Universe to be finite but without boundaries; its temporal character is such that it had a discrete beginning but will keep on existing and growing into the infinite future unless there is sufficient [as yet undiscovered] mass to provide gravitational forces that slow the expansion and eventually cause contraction [collapse].
A much different model considers the Universe to be infinite in time and space - it always was and always will be philosphically, there are concepts that equate God as an "intellectual presence" distributed throughout this naturalistic Universe. These and other important ideas - whether the Universe's shape is analogous to spherical, hyperbolic, or flat; whether it is open or closed, whether it is presently decelerating or accelerating, and whether it is infinite or finite in time and space - are treated in detail on pages, and By the end of the second quarter of the 20th Century, most models for the Universe's behavior considered expansion of some sort as an outcome.
Einstein, in particular, showed that any three-dimensional expansion must also consider the effects of the fourth dimension - time - to account for the behaviour of light traveling great distances in a vast "volume" without known boundaries making up what we conceive of as "space".
He also deduced that space must be curved and light and other radiation will therefore follow curved paths as the shortest distance between widely separated points and would, in his view, expand dynamically in a 4-dimensional spherical geometry a spacetime dimensionality.
Einstein, at least in his early thinking, also considered the Universe to be finite and eternal. The next figure is a spacetime diagram that summarizes the history of the expanding and evolving Universe in terms of what is popularly known today as the general or Standard Big Bang B. It received its descriptive name as a derisive comment from the astronomer Fred Hoyle, then precept of expansion, who advocated instead a Universe of constant size as described in his Steady State model; variants of this and other models have been put forth, as described on page Simply stated, the Standard Big Bang model holds the Universe to have expanded from a infinitesimally small point.
In essence, the Big Bang is the creation event that started the Universe and determined its ultimate course of evolution through the state now observed and into its long term perhaps infinite future. You can access it by clicking here.
Note that most temperatures are expressed in energy equivalents as eV's or electron volts GeV refers to Giga-electron volts.
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To return to the present page, you will need to hit the X button on the upper right of the screen that comes up with your browser. The Big Bang as an expansion theory traces its roots to ideas proposed by A. Friedmann in to counter ideas attendant to Albert Einstein's Theory of General Relativity, from which that titan had derived a model of a static, non-expanding, eternal universe he eventually abandoned this model as evidence for expansion was repeatedly verified and he realized his General Relativity proved very germane to the expansion models.
The Abbe George Lemaitre a Belgian priest in set forth another expansion model that started with his proposed "Primeval or Primordial Atom", a hot, dense, very small object that resembles the "singularity", a term more widely accepted.
The nature of a Big Bang was refined and embellished by G. Gamow and others in the s. Confirming evidence for expansion came from Edwin Hubble in the late s.
The Big Bang can be mentally related to the above-mentioned singularity by imagining that the expansion is run in reverse like playing a film backwards: As described later in this Section pagethe B. The Universe has been enlarging ever since this first abrupt explosion, with space expanding, and galaxies drawing apart, so that the size of the knowable part of this vast collection of galaxies, stars, gases, and dust is now measured in billions of light years representing the distances reached by the fastest moving material [near the speed of light] since the moment of the Big Bang [14 to 15 billion years ago].
This age or time since inception is determined from the Hubble Constant H which may change its value which is derived from the slope of a plot of distance to stellar or galactic sources of light versus the velocity of each source see page Aside from quantum speculation, nothing is really known about the state of the Universe-to-be just prior to the initiation of the Big Bang a moment known as the Planck Epoch.
The Laws and the 20 or so fundamental parameters or factors that control the observed behavior of all that is seeable in the Universe become the prevailing reality at the instant of the Big Bang, but Science cannot as yet account for the "why" of their particular formulation and values, i.
Among these conditions that had to be "fine-tuned" just right is this partial, but very significant list: See also another list at the bottom of page a. Best postulates consider the singularity whatever its origin at this instant to be governed by principles underlying quantum mechanics, have maximum order zero entropy [see page ]and be multidimensional i.
Quantum theory does not rule out discrete "things" some form of energy or matter to have existed prior to the inception of the Planck Epoch; on the other hand, this existence is not required or necessary.
Molecular Orbital Diagram For A Simple Pi Bond – Bonding And Antibonding — Master Organic Chemistry
But, as implied above and discussed in detail on page"fluctuations" within possible energy fields in a pre-Universe quantum state an abstract but potentially real condition that runs counter to philosophical notions of "being" may have been the triggering factor that started the B. This theory allows cosmologists to begin the Universe at a parameter called the Planck timegiven as seconds what happened or existed at even earlier time is not knowable with the principles of physics developed to this day.
At that instant, the Universe must have been at least as small at meters - the Planck length about the same size as a string in superstring theory [see below]. During this fraction of a second interval, gravity then was as strong as the other forces. Its tendency to hold the singularity together had to be overcome by the force that activated the Big Bang.
The onset of fundamental force separation may have been tied to the force driving Inflation see below. But gravity thereafter rapidly decreased in relative strength so that today at the atomic scale it is 2 x weaker than the electrical force between a proton and an electron according to one recent theory, gravity remains strong until about seconds. However, since the forces between protons positive and electrons negative are neutralized balanced in ordinary matter, the now much weaker gravitational forces are the major residual force that persists and acts to hold together collective macro-matter at scales larger than atoms, specifically those bodies at rest or in motion subject to and described by Newton's Laws; includes those aspects of movements of planets, stars, and galaxies that can be treated non-relativistically.
And gravity has the fortunate property of acting over very long distances decreasing as the inverse square law. Although we think of gravity as the most pervasive force acting within the Universe, there is growing evidence that some form of gravity-like force also resides within an atom's nucleus but extends its effects over very short atomic scale distances. The non-gravity forces that separated from the gravitational force are described by the still developing Grand Unified Theory or GUT, which seeks to explain how they co-existed.
The GUT itself is a subset of the Theory of Everything TOE which, when it is finally worked out, will specify a single force or condition or, metaphysically, a state of Being that describes the situation at the very inception of the Universe.
Thus, TOE unites the gravity field with the quantum field within the singularity that emerged as separate entities almost instantaneously at the start of the Big Bang. The TOE speculates on what may have existed or happened prior to the Big Bang, based on both quantum principles and belief that some other type of [pre-Bang] physics yet to be developed governed the pre-Universe void. At the Planck time, the four fundamental forces are said to be united the Unified Epoch.
The flow chart below see also the third figure below specifies the major components of each of the forces as they are assumed to exist after the first minute of the Big Bang.
When unified at the outset of the Big Bang, they are presumed to exist in a state shown by the? One model, now gaining some favor, based on Superstring theory see last paragraph on this page contends that at the first moment of the Big Bang at the sec mark; before which any singularity or other state of existence cannot yet be described by present physics the Universe-to-be consisted of 10 dimensions. As the process of the Universe's birth starts, six of those dimensions collapse but presently exist on microscales as small as centimeters and the remaining four three spatial; one time enlarged to the Universe of today.
The behavior of these forces in the earliest moments of the Big Bang was critical to the construction and development of the Universe as we perceive it today. Gravity in particular controls the ultimate fate of the Universe's expansion see below and formation of stars and galactic clusters. According to Einsteinian Relativity, gravity, which we intuitively perceive as attractive forces between masses, is a fundamental geometric property of spacetime that depends closely on the curvature of space, such that concentrations of matter can "bend" space itself; Einstein and others have predicted the existence of gravitational waves that interact with matter; see the Preface for additional treatment.
For all its importance, it is surprising that gravity is by far the weakest of the four primary forces; its role in keeping macro-matter together and controlling how celestial bodies maintain their orbits is just that it becomes the strong, action-at-a-distance force left whenever the other forces are electrically neutral and have influence only out to very short distances.
Between and sec a minuscule but vital interval of time - about a billionth of a trillionth of a trillionth earth seconds - referred to as the Inflationary Stage a mechanism to explain certain properties of the Universe was first proposed by Alan Guth, then at Princeton Universityto explain some aspects of the Universe [see below]; that were serious difficulties in the Standard Model.
The theory holds that the nascent and still minute Universe underwent a major phase change probably thermodynamic in which repulsion forces caused a huge exponential increase in the rate of expansion of space.
Through this brief moment approximately a trillionth of a trillion of a trillionth  of a secondthe micro-Universe grew from an infinitesimal size but still containing all the matter and energy [extremely dense] that was to become the Universe as it is now to that of a grapefruit or perhaps even a pumpkin.
This is an expansion factor that may have been between and this is the range of uncertainty, although some theoreticians choose as the more likely number. This extreme growth determined the eventual spatial curvature of the present Universe in the most "popular" model, tending towards "flat".
This next diagram illustrates the extreme growth of the incipient Universe during the Inflationary moment both horizontal and vertical scales are in powers of ten ; in the version shown, the Big Bang expansion is shown as decelerating over time but a vital modification is discussed on page page During this critical moment, the physical conditions that led to the present Universe were preordained.
The driving force behind this huge "leap" in size which has happened at this extreme rate only once in Universe history is postulated by some as a momentary state of gravity as a repulsive negative force perhaps equivalent to Einstein's once-defunct Cosmological Constant but in a new form: The source of the energy that powered Inflation has not been precisely identified but the separation of gravitational force from the remaining three forces see third diagram below may have released a huge amount of energy capable of bringing about the repulsion that marks inflation see paragraphs on page that describe Einstein's Cosmological Constant which depends on a similar repulsive energy related to an as yet undiscovered but apparently real "dark energy".
During the brief inflationary period, different parts of the still "empty" void energy existed but the first particles that would form matter had not yet appeared and organized separated at a rate greater than the speed of light - in effect, it was this initial evolving dimensionality or space that was expanding.
Recent discoveries indicate that the Universe is now undergoing a second but relatively much slower rate of accelerating expansion that has turned around the post Big Bang gravitationally-mandated deceleration, beginning at some [still undetermined] stage [probably prior to the last 7 billion years] of the Universe's growth; see page During inflation, as gravity began to act independently, gravitational waves were produced that had a critical bearing on the minute but vital variations in distribution of temperatures and matter in the subsequent history of the Universe as we know it.
As time proceeded, gravity then reverted to the attractive force that took over control of further expansion. Specifically, a metastable state called the false vacuum - devoid of matter per se but containing some kind of energy - underwent a decay or phase change by quantum processes to a momentary energy density that produces the negative pressure capable of powering the inflation.
In this case, you have two positively charged nuclei held closely together in space but no electrons between them providing a stabilizing attractive interaction. The repulsion between the two nuclei and the electrons with each other outweighs any attractive forces between the electrons and nuclei, and the result is more unstable than the situation for two non-bonded atoms.Molecular Shape and Orbital Hybridization
Why do we have to concern ourselves with a situation that is even more unstable than for two atoms being apart? The high-energy electron can then just relax back to ground state, emitting a photon in the process, and the molecule is back to where it started. The answer is that there is a limit to how many electrons a bonding orbital will hold. No electrons may have the exact same quantum number. Hence, when we populate our energy diagram with electrons, the most that any individual orbital can accommodate is two.
Note the opposite spins in the bonding molecular orbital. For the 2p orbital, the node resides directly at the nucleus. The 2s and 2p orbitals each have one node, the 3s and 3p two, and so on. The bonding in hydrogen H2 is a perfect example.
The number of orbitals is never changed by bonding. The number of molecular orbitals always equals the number of contributing atomic orbitals. The second molecular orbital is described by destructive overlap or destructive interference, if you prefer where p orbitals of mismatched phase join together to form another pi molecular orbital.
Hence it is higher in energy. By analogy to our previous examples, we can draw up an energy diagram for these two situations. The energy of the antibonding orbital is a little bit more than 2 times the bonding energy.
Some Rules for Pi Molecular Orbitals Hopefully most of this was a review from first-semester material.