The beginning student of chemistry must have a knowledge of the theory which forms the basis for our understanding of chemistry and he must acquire this knowledge before he has the mathematical background required for a rigorous course of study in quantum mechanics. The present approach is designed to meet this need by stressing the physical or observable aspects of the theory through an extensive use of the electronic charge density.
The manner in which the negative charge of an atom or a molecule is arranged in three-dimensional space is determined by the electronic charge density distribution. Thus, it determines directly the sizes and shapes of molecules, their electrical moments and, indeed, all of their chemical and physical properties.
Since the charge density describes the distribution of negative charge in real space, it is a physically measurable quantity. Consequently, when used as a basis for the discussion of chemistry, the charge density allows for a direct physical picture and interpretation.
In particular, the forces exerted on a nucleus in a molecule by the other nuclei and by the electronic charge density may be rigorously calculated and interpreted in terms of classical electrostatics. Thus, given the molecular charge distribution, the stability of a chemical bond may be discussed in terms of the electrostatic requirement of achieving a zero force on the nuclei in the molecule. A chemical bond is the result of the accumulation of negative charge dens...
In this essay, the author
- Explains that the present approach emphasizes the physical or observable aspects of the theory through an extensive use of electronic charge density.
- Explains how the electronic charge density distribution determines the negative charge of an atom or a molecule in three-dimensional space.
- Explains that the charge density describes the distribution of negative charge in real space and allows for a direct physical picture and interpretation.
- Explains how classical electrostatics calculates the forces exerted on a nucleus in the molecule. a chemical bond is the result of the accumulation of negative charge density.
- Explains that the classifications of bonding, ionic or covalent, are retained, but they are given physical definitions in terms of the actual distribution of charge within the molecule.
- Illustrates the need for a new mechanics to describe the events at the atomic level through experiments with electrons and light, which are found to be inexplicable.
- Explains that chemical binding is discussed in terms of the molecular charge distribution and the forces which it exerts on the nuclei, an approach which may be rigorously presented using electrostatic concepts.
- Describes the topics covered in the first seven sections of this web page. the final section is for the reader interested in extension of the orbital concept to the molecular cases.
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- Oscillations Essayexplanatory essayThe problem of small oscillations can be solved through the study of molecular vibrations which further, can be introduced by considering the elementary dynamical principles. The solution for the problem of small oscillations can be found out classically, as it is much easier to find its solution in classical mechanics than that in quantum mechanics. One of the most powerful tools to simplify the treatment of molecular vibrations is by use of symmetry coordinates. Symmetry coordinates are the linear combination of internal coordinates and will be discussed later in detail in this chapter.
In this essay, the author
- Explains that in the expression of potential energy (v) given by equation (2.03), the higher order terms can be neglected for sufficiently small amplitudes of vibration.
- Explains that t is a function of velocities only, and v is an equation of coordinates only.
- Explains that secular equations can be solved by substituting for q_j.
- Explains that by substituting equation (2.11) in equation (2.10), a set of algebraic equations will be obtained which can be written as
- Explains that the secular determinant for the non-vanishing solution is given by the equation (2.12).
- Explains that the polynomial is of order n and thus provides the roots of. the determinant is the coefficients of the unknown amplitudes aj in the set of equations.
- Explains that n_k are the constants and can be determined by the initial values of q_j and
- Explains that the problem of small oscillations can be solved through the study of molecular vibrations.
- Explains that the lagrangian, l in terms of kinetic energy and potential energy is given by equation (2.05).
- Explains that by substituting the expressions of t and v in equation (2.09), we get d/dt.
733 wordsRead More - Physicsexplanatory essayCharles-Augustin de Coulomb invented a device, dubbed the torsion balance, that allowed him to measure very small charges and experimentally estimate the force of attraction or repulsion between two charged bodies. The data he obtained through his extensive use of the torsion balance enabled Coulomb to formulate one...
In this essay, the author
- Explains that benjamin franklin identified lightning with electricity when he discovered that lightning conducted, or flowed, through a metal key could be used to charge jars.
- Explains that franklin was the first person to estimate the size of atoms. he measured the ripples off the water surface.
- Explains that robert millikan had an oil drop experiment, though his experiment involved balancing the downward gravitational force with the upward drag and the electric forces on tiny charged droplets of oil between the two metal electrodes.
- Explains that millikan won the nobel prize in physics because of his experiment. the charge on a single electron was 1.5921019 c.
- Describes charles-augustin de coulomb's device, the torsion balance, that allowed him to measure very small charges and experimentally estimate the force of attraction or repulsion between two charged bodies.
- Explains coulomb's law, which describes the electrostatic interaction between electrically charged particles. it states that the magnitude of the force between two point charges is directly proportional to the charges of two objects.
- Explains that ernest rutherford contributed to the planetary model of the atom because he originally thought atoms were filled with empty space, but tested this theory with his gold foil experiment in which proved it wrong.
- Describes how rutherford's experiment was possible with gold foil and a beam of alpha particles.
- Explains why protons and electrons don't contact is because they are in motion. an attractive force between two particles can result in a circular orbit, with the particles keeping the same distance apart.
- Explains how an electric field becomes so intense that electrons are repelled into the earth's surface by the strong negative charge at the bottom of the cloud.
654 wordsRead More - Single Molecule Spectroscopy Essayexplanatory essayFig 1: Applications of single molecule spectroscopy in solving scientific problems in Physics, Chemistry and Biology
In this essay, the author
- Explains that the progress in single molecule detection and single-molecule spectroscopy (sms) has proved to be a boon.
- Explains the applications of single molecule spectroscopy in solving scientific problems in physics, chemistry and biology.
- Explains that fluorescence studies of single molecule detection and spectroscopy have proved to be advantageous in many ways.
- Explains that detection of single molecules separately prevents concealing of information hidden by ensemble averaging. it helps to obtain distributions and spectra of different species in heterogeneous environments.
- Explains hirschfield's discovery of the virometer, which could detect, classify, and detect single viruses using the type of nucleic acid and fluorescing molecules.
- Explains that keller and his colleagues improved the detection limits two folds as compared to the previous experiments. they mainly concentrated on molecules in hydrodynamic focused flows using a modified cytometer to detect fluorophores in attogram quantities.
- Explains that with further advancements, there was a major leap in reducing background signals from the spectra of single molecules by employing the principle of total internal reflection coupled with wide field microscopy and charge coupled device cameras for detection.
- Explains the recent development of methods to detect molecules which flow or diffuse in solutions. these give information about the size, diffusion coefficient and concentration of various constituents of the macromolecule.
- Explains the basic principles of fluorescence spectroscopy to its application and development in single molecule studies.
- Explains that fluorescence and phosphorescence are a spin-free process. quenching is the major competition to the radiative processes, which negates the effects.
- Illustrates a jablonski diagram where the fluorescence emission lines are stokes-shifted. this difference in wavelengths is employed in detecting biomolecules.
- Explains that fluorescence's emission spectrum is not dependent on the excitation wavelength. this happens because species excited to a higher vibrational energy state relaxes to its lowest vibration.
- Explains that fluorescence emission spectrum and absorption spectrum are mirror images as in both cases the transitions involved are similar.
- Explains that anthracene's mirror-image spectrum differs from that of other biochemical fluorophores like tyrosine due to differences in absorbing and emitting species.
- Describes a phenomenon called resonance energy transfer (ret) or more commonly fluorescence energy transport (fret). the transfer is dependent on the distance between the two molecules and the extent of their spectra overlap
- Explains the two most important parameters of a fluorophore, the quantum efficiency, and the fluorescence lifetime.
- Explains the quantum efficiency of a fluorophore when there are no non radiative processes.
- Explains that the rate of radiative emission (spontaneous emission) can be estimated from the fermi’s golden rule. the fluorescence decay rate is proportional to the projected local density of the photonic modes.
- Explains that in biochemical fluorophores there is a lot of deviation in the values calculated using the above equation and values from the spectra (absorption/ emission).
- Explains that fluorescence anisotropy relies on the photoselective excitation of the sample using a light which is polarized.
- Analyzes the effects of polarized irradiation and rotational diffusion on the fluorescence anisotropy.
- Explains that the properties of absorption and fluorescence spectra, lifetime of the fluophore, anisotropy and quantum yield are the five intrinsic physical variables which are probed in a smfs experiment.
- Explains that smfs requires certain sophistications in the techniques. the main source of background in spectra is from raman and rayleigh scattering and fluorescence due to solvent or other optical components.
2467 wordsRead More - Determining The Polarity Of 2-Decomplete Moleculesexplanatory essayIn this experiment, we computationally predicted the dipole moments of 5 different analyte molecules using the program Spartan. We constructed the molecules online as the program then calculated their dipole moments (polarity). We then experimentally determined the 5 analyte molecules retention factors using the TLC method in the lab. Polarity in organic chemistry refers to a separation of electric charge leading to a molecule having an electric dipole moment1. To determine whether a molecule is polar or nonpolar depends on a molecules structure. This is done by comparing the electronegativity’s of each element in the molecule that are bonded to each other. If a molecules dipole moment eliminates each other due to its symmetrical shape, it is considered to be
In this essay, the author
- Explains how they computationally predicted the dipole moments of 5 different analyte molecules using the program spartan.
- Explains that chromatography is used to separate different molecules for their identification. the stationary phase is the interaction between the solvent and the molecules intermolecular forces.
- Explains possible errors in the program spartan, such as not building the compounds correctly and not placing enough solution on the plates, affecting the results of rf values.
549 wordsRead More - Chemical Bondingexplanatory essayThe development of quantum mechanics in the 1920's and 1930's has revolutionized our understanding of the chemical bond. It has allowed chemists to advance from the simple picture that covalent and ionic bonding affords to a more complex model based on molecular orbital theory.
In this essay, the author
- Explains that chemical reactions involve the making and breaking of bonds. to understand bonds, they will first describe several of their properties.
- Explains that there are two fundamental types of bonds--covalent and ionic. covalent bonds are formed between atoms of approximately equal electronegativity.
- Explains that covalent molecules can take on many shapes, from simple linear molecules like h2 to complex chains of atoms like butane.
- Explains how quantum mechanics revolutionized our understanding of the chemical bond. molecular orbital theory provides a valuable theoretical complement to traditional conceptions of ionic and covalent bonding.
490 wordsRead More - Dielectric Substance Essayexplanatory essayAtom consists of a center core called the nucleus all the protons reside inside the nucleus and the negatively charged electrons revolve around the nucleus. In the Dielectric materials Nucleus has a weak hold on its electrons so when the dielectric substance is placed in the external Electric Field then force is applied on the proton and the electrons of the dielectric substance and the protons slightly displace along the direction of the electric field and the electrons displace in the direction opposite to the electric filed so this process of shifting of charges from its normal position is called dipole moment (µ) and the atom or molecule is called dipole.
In this essay, the author
- Explains that dielectric-substances have a unique property that they get polarized when it is placed in electric filed. positive charges displace towards the low potential end or in the direction of the electric filed.
- Explains that when the dielectric substance is placed in an external electric field the positive and negative charges in the dielectric substance move slightly towards the negative potential. this process is called polarization.
- Explains that the atomic model for atoms consist of positive and negative charges called electrons and protons. in the dielectric materials, the nucleus has a weak hold on its electrons.
- Explains that electronic polarization occurs in all types of insulators including the ionic and the orientation polarization dielectric substances.
- Explains that ionic substances are formed by the transfer of the electron form one atom to another bonding
- Explains that dielectric strength is the maximum voltage a material can withstand before its breakdown. it is measured through the thickness or width of the material and measured in volts per meter.
- Explains that if a dielectric substance is placed in the electric field, the material gets polarized or the dipoles get aligned.
- Explains how a current is passed through the dielectric material and high voltage is applied across the ends of the electrodes.
- Explains that ozone generators use the dielectric substance called borosilicate glass and the aluminum foils as the electrodes.
- Explains that the dielectrics are also used in plasma displays and work on the principle of discharge.
- Explains that these lasers are produced on the dielectric discharge phenomenon through the carbon-di-oxide which is a dielectric material.
- Explains that dielectric substances such as praline are coated on the surface of the materials, which will form a barrier between the substance and the environment.
- Explains that the dielectric oil used in transformers is a synesthetic or natural substance like mineral oil, organic esters are silicon oil etc.
- Explains that the bit rate of mos dram’s is increasing and the area of the capacitors are decreasing, so we use dielectric materials with a higher dielectric constant like zr-oxide.
- Explains the dielectric constant of a dielectric substance, which is the relative primitively of the material, and its ability to concentrate the flux lines to cancel the applied electric field.
- Explains that rotational polarization occurs in polar molecules like water (h2o) consists of permanent dipoles.
- Explains that the dielectric dispersion depends on the frequency of the applied electric field and the rate of polarization.
- Explains the effect of removal of the dielectric substance from the electric field on its dipole moment.
- Explains that when the voltage across the dielectric material is increased continuously a point reaches at which the insulator starts conduction current.
- Explains the importance of keeping a small gap between the plates of the capacitors for the purpose of allowing higher capacitance.
2136 wordsRead More - Wiliiam Shockley-Autobiographyexplanatory essayWilliam Shockley was born on February 13, 1910 in London, England. He is most famously noted for winning the Nobel Prize in physics in 1956. He won this for being the co-inventor of the transistor with John Bardeen and Walter Houser Brattain. Shockley’s parents were both Americans. His father, William Hillman Shockley, was a mining engineer born in Massachusetts. His mother, Mary Bradford, was a federal deputy surveyor of mineral lands. They returned to America when William was just a baby. They both were very encouraging for his love and passion for science, as well as his neighbor who was a professor of physics at Stanford. He got his B. Sc. Degree at the California Institute of Technology in 1932. Four years later he got his PhD from the Massachusetts Institute of Technology (MIT). He wrote his doctoral thesis on the energy band structure of sodium chloride. The title of this thesis was “Calculation of Electron Wave Functions in Sodium Chloride Crystals.”
In this essay, the author
- Explains that william shockley won the nobel prize in physics in 1956 for co-inventing the transistor with john bardeen and walter houser brattain.
- Explains that after graduating from mit, he went straight into work at bell laboratory. he did most of his research in solid state physics, especially vacuum tubes.
- Narrates how shockley worked on military projects from world war ii. he was research director of the anti-submarine warfare operations research group and expert consultant in the secretary for war.
- Describes how shockley's idea of using field effects and applying the quantum theory to the development of semiconductors led to bardeen and brattain creating a point-contact transistor.
- Explains that william shockley and his team were credited for discovering the transistor effect in 1947 and developing the first device.
- Narrates how shockley resigned from the transistor physics department in 1955 and became the director of the beckman semi-conductor laboratory in mountain view, california.
- Narrates how shockley left his company to become a professor at standford university, where he received the holley medal of the american society of mechanical engineers.
- Analyzes how shockley's philosophies were similar to those of the eugenics movement. he was the only scientist to donate sperm to the repository for germinal choice
- Explains that william shockley was married twice, once to jean bailey and then to emmy lanning, and had three children by his first marriage, two sons and one daughter.
1134 wordsRead More - Essay On The Cartoon Guide To Chemistryexplanatory essayThe author’s purpose in writing this book is many. One of these is to give students knowledge in the basics of chemistry. This book is an introduction to the life of chemistry itself. The theme of this book are elements, atoms, the periodic table, matter, chemical reactions, thermodynamics, DNA, electrochemistry, reaction rate, equilibrium, solutions, and much more! More broadly, the theme if this book is chemistry and its importance of it in our lives. There were many main points interesting to me, but here are a few.
In this essay, the author
- Explains that the atom is mostly filled with empty space, yet it consists of protons and neutrons which are in the nucleus.
- Opines that larry gonick and craig criddle achieved their goal by writing this effective and powerful book.
- Opines that the cartoon guide to chemistry by larry gonick and craig criddle is a wonderful book to read.
- Explains that the book is called the cartoon guide to chemistry by larry gonick and craig criddle. it contains 244 pages of pure knowledge of chemistry.
- Explains that atoms combine with each other by exchanging or sharing electrons.
1384 wordsRead More - Solid State Lasersexplanatory essayKittel, C. (2005). Introduction to Solid State Physics, 8th ed. John Wiley & Sons, Inc.
In this essay, the author
- Explains that solid state lasers, although a 50-year-old technology, have remained relevant. however, due to the crystal laser medium, there are many considerations specifically inherent to them.
- Explains einstein's quantum theory of radiation, which established conditions in which we could predict the number of excited states of electrons in an atom that could spontaneously emit a photon.
- Explains that atoms can only absorb photons of certain wavelengths carrying the amount of energy necessary to raise the state of the electron.
- Explains that at thermal equilibrium the lower energy states are more populated than the higher states, so no net energy is emitted.
- Explains that the laser system consists of three basic components: the pump, the resonator cavity and the gain medium.
- Explains that the optical resonator chamber reflects the produced photons back into the gain medium.
- Explains that the gain medium consists of a host crystal doped with active ions. only transitions whose radiative decay are decoupled from lattice vibrations of the host have long metastable states with narrow linewidth necessary for laser action.
- Explains that higher gap transitions require frequencies higher than the lattice vibrational frequencies, so spontaneous phonon emission cannot occur. a good host material must have proper mechanical, thermal and optical properties.
- Explains that thermal conductivity is also an important consideration with regard to the power levels required for lasing.
- Explains that medium geometry influences the macroscopic properties of the laser system. slabs and tubes have greater cooling surfaces and increase system efficiency.
- Explains that different materials have different properties whose assets must balance their liabilities. for example, oxides have high thermal conductivity, narrow linewidth and hardness, but they have poor homogeneity of active ions.
- Explains that yttrium aluminum garnet will be the focus because of its commercial predominance. nd:yag has high thermal conductivity and hardness similar to sapphire.
- Explains that solid state lasers have unlimited applications and the technology has considerably progressed over the last fifty years. the physics involved, however, do not stray far from the basic principles.
- Cites almed, h. (n.d.). doped insulator lasers. collins, r.
- Explains that geusic, j. e. and koechner, w. (2006). solid state laser engineering.
1630 wordsRead More - Nuclear Chemistryexplanatory essaySmith, Roland. Conquering Chemsitry: HSC course. 4th ed. Vol. 1. N/A: Cengage Learning Australia, 2010. 74-90. 1 vols. Print.
In this essay, the author
- Explains that the half-life of a radioisotope is the time required for half the atoms in the sample to undergo radioactive decay.
- Explains that alpha particles can produce transuranic elements. when plutonium-239 is bombarded, an isotope of curium is formed.
- Explains that commercial radioactive isotopes are used for commercial/industrial use such as medicine, e.g. cobalt-60 for cancer treatment.
- Explains that suitable target nuclei are placed in the reactor and are bombarded with neutrons as reactors contain large sources.
- Explains that a cyclotron is used in some medical radioisotope production.
- Explains that equipment using radiation must be checked to make sure the radiation is only directed to where it is intended for use and not escaping where humans can become exposed.
- Explains that alpha particles are the nuclei of a helium atom 42he, consisting of two protons and two neutrons, positively charged.
- Explains that transuranic elements are elements that have been artificially synthesised and have atomic numbers greater than 92 neutron bombardment: neptunium can be made in nuclear reactors by neutron bombardment of uranium-238, achieved in 1940.
- Explains how ion accelerators produce higher atomic numbers by firing accelerated particles into a target. nuclear reactions occur in the target nuclei and are then analysed.
- Identifies radioisotopes used in industry and medicine and explains their properties.
- Analyzes the benefits and problems associated with the use of radioactive isotopes in industries and medicine.
- Explains that people working around radioactive substances must wear radiation badges that record the amount of radiation they have received.
- Identifies three instruments or processes that can be used to detect radiation and explains how each one functions.
- Explains that the gm is used to measure the strength of ionising radiation. beta radiation is readily detected, but other forms of radiation can also be detected.
- Explains the discovery of element 114 by bombarding a 24494pu target with 4820ca ions. the resulting isotope decayed further by alpha emission.
- Cites levy, joel, and smith, roland. conquering chemsitry: hsc course. n/a: cengage learning australia.
1999 wordsRead More