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    Atoms & Molecules

    Atoms and molecules are the basic building blocks of all “normal” matter in the universe. They make up everything from the simple chemical bonds of water to complex structures like humans. Atoms and molecules have different charges and configurations which create different structures with different properties.

    An atom consists of a dense central nucleus that is surrounded by a “cloud” of negatively charged electrons. The nucleus contains positively charged protons and neutral neutrons. The electrons are bounded in the nucleus by an electromagnetic force. Atoms will group together by chemical bonds based on the force of the atoms to create chemical bonds.

    Atoms will be positive, negative or neutrally charged based on the number of protons and electrons. If an atom is positive or negatively charged it is referred to as an ion. Atoms are classified based on the number of protons and neutrons in the nucleus. Atoms can be different sizes with respect to the number of proton, neutrons and electrons in the atomic configuration.

    A molecule is an electrically neutral group of two or more atoms that are held together by covalent chemical bonds. Molecules are different from ions due to the neutral charge they maintain. Molecules, like atoms, can take on different sizes and configuration based on the type of atoms and the length of the bonds. Molecules are distinguished by their molecular formula, which is defined by the ratio of atoms involved in creating the molecule.

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    The De Broglie wavelength in A.U. of an electron

    Show that the De Broglie wavelength in A.U. of an electron where a narrow beam of electrons is accelerated by a potential difference of V volts is given by lemda = [12.28/V^(1/2)][eV/(2m_o c^2) +1]^(1/2) The complete problem is in the attached file.

    Mean Free Path & Surplus Uranium

    See the attached file. (g) Define the 'mean free path' for a neutron in a material. Water is used as the moderator in a PWR. Calculate the mean free path of a thermal neutron in water given that the absorption cross section for thermal neutrons in water is o = 0.66 barns. What are the consequences for the spacing of the fu

    The sizes of highly excited atoms.

    a) Calculate the radius r_n of a hydrogen atom whose electron is Bohr orbit n. Evaluate your result for n = 50, 100 and 500. b) As mentioned in the text, transitions between such highly excited states of hydrogen have been observed. For instance, an emission line has been observed with radio telescopes at a frequency of 5009

    The spacing of atoms in a sodium chloride crystal.

    The crystal lattice of sodium chloride has ions of sodium (Na+) and ions of chlorine (Cl-) arranged alternately in a simple cubic array. Thus the crystal volume per ion is d^3, where d is the distance between the centers of adjacent ions. The molecular weight of NaCl is 58.45 and its density is 2.164 g/cm^3. a) Calculate the v

    Surface Tension of a Surfactant Molecule's Aqueous Solution

    The surface tension of an aqueous solution of a surfactant molecule is measured as a function of concentration. The data is shown attached in a plot of surface tension vs. weight percent surfactant. In a few sentences, explain what is happening and why. How will the appearance of the solution differ at 0.001 weight percent versu

    The Uses of Spectroscopy

    What do scientists use spectroscopy for? Research the uses of spectroscopy and describe a use, and what we have learned from this use.

    "What is an Atom?" Exercise Sheet for Science Students

    Take a clear balloon. Add one BB and blow up the balloon to about the size of a softball, then tie it off. 1. What is an atom? What is the charge of a proton, neutron, and electron? What does this balloon represent? What does the BB represent? 2. The diameter of a proton is approximately 1 x 10^-15 meters. The diameter

    Estimates in Ni-Cu Alloy.

    A Ni-Cu alloy is prepared which has a lattice constant of 0.354 nm. The maximum magnetization of the alloy is measured as 1.25*10^6 A/m. Assuming no interactions between Ni and Cu atoms, and the magnetization comes from the all unpaired 3d Ni electrons.Estimate the wt. % Cu in the alloy. Both Ni and Cu have a fcc structure wit

    Plasma frequency

    Conductors are characterized by a plasma frequency ωp that for a particular conductor is a constant corresponding to wavelengths well into ultraviolet. The conductor becomes transparent for frequencies greater than the plasma frequency, with an index of refraction that is less than one. Please see the attachment for the ful

    harmonic vibrational frequency vibrational anharmonicity

    For the 127I35Cl molecule, the following transitions are detected in the infrared. From this data, deduce the harmonic vibrational frequency (? ?_e) and the vibrational anharmonicity (? ?_e x ?_e), both in units of cm-1. Note that the following are the result of careful spectroscopic study that can detect weak, "forbidden" tr

    Hamiltonian operator and calculation of force

    1] Write down the Hamiltonian operator for the following problems: a. Particle in a box (of length L) b. Free Particle c. Harmonic oscillator 2] In the infrared spectrum of H79Br there is an intense line at 2.60 X 10^3 cm^-1. Calculate the force constant of H^79Br and the period of vibration.

    What is the magnitude of the resultant force?

    I really need help and in-depth explanations on how to do these problems from the online practice test. 1. Use the following working values for the physical constants: Acceleration due to gravity on the surface of the earth: g = 10 m/s^2 Speed of light in a vacuum: c = 3.0 x 10^8 m/s Charge of an electron: Qe = 1.6 x 10^-1

    Wall pressure nitrogen molecules

    4.60 x 10^23 nitrogen molecules (N_2) collide with a 18.0 cm^2 wall each second. Assume that the molecules all travel with a speed of 400 m/s and strike the wall head on. What is the pressure on the wall?

    The message of radiation from space

    What are the three types of spectra emitted from hot objects? How are spectral lines formed from hydrogen atoms? How are spectral lines formed from molecules? What kinds of information can we get from spectral lines?

    Average value of force

    The force acting between an electron and proton in a hydrogen atom is F=(-e^2)/(4&#960;&#1013;_o r^2 ) . Calculate the average value of this force, <F>, for an electron in 1s state of the hydrogen atom.

    Milk Standing in Water in Porous Pot: Example Problem

    Explain why a bottle of milk keeps better when it stands in water in a porous pot in a draught. Some water is stored in a bag of a porous material, canvas, which is hung where it is exposed to a draught of air. Explain why the temperature of the water is lower than that of the air.

    Understanding the universe through knowledge of the atom

    What is the difference between an atom and an ion? Provide an example. Describe two ways an atom can be excited. Why should photons emitted by a hotter material have an average shorter wavelength? Atoms produce spectra. Distinguish between a continuous, a bright-line, and an absorption spectrum by describing hw each i

    Significant Figures and Conversion of Units

    1. A fisherman catches two striped bass. The smaller of the two has a measured length of 93.46 cm(two decimal places, four significant figures), and the larger fish has a measured length of 135.3cm (one decimal place, four significant figures). What is the total length of fish caught for the day? 2. How many significant figu

    Band structure and a weak periodic potential

    4. Discuss briefly the origin of the differing electronic properties of metals, semiconductors and insulators. Under what circumstances will the nearly-free electron model be useful for describing the band structure of a solid? A weak periodic potential W(z) = W_0 cos (2*pi*z)/a with W_0 > 0, is imposed on a one-dimensi

    Microscopic globules

    Homogenized milk is composed of microscopic globules of fat suspended in a watery medium. Is homogenized milk a true solution? Why?

    Types of Light Spectrum's of Different Sources

    Two light sources are provided: a hydrogen discharge tube and a filament lamp. Each can be viewed through a grating fixed to the glass case. If you maneuver your eye until you see a bright fringe pattern, which type of spectrum you see for each light source?

    KCl molecule-- Periodic motion

    An approximation for the potential energy of a KCl molecule is U=A[(R^7/8r^8)-(1/r)], where R=2.67*10^-10m and A=2.31*10^-28J*m. a. Using this approximation find the radial component of the force on each atom. Express your answer in terms of the variables A, R0 and r. b.Find the equilibrium separation. c. Find the

    Mean Scattering Time of a Molecule

    Show that the mean-scattering time of a molecule travelling at speed v is tau = 1/n*sigma*v (see attachment for symbolic equation) where n is the molecular density and sigma is the collision cross section. Estimate the mean time between collisions of nitrogen molecules at sea level in the Earth's atmosphere assuming th

    Heat Capacity of Nitrogen

    Experimental data for the heat capacity of N_2 as a function of temperature are shown in the table below. T (Kelvin) 170 500 770 1170 1600 2000 2440 C/Nk_B 2.5 2.57 2.76 3.01 3.22 3.31 3.4 (i) Estimate the frequency of vibration of the N_2 molecule. (ii) By making a rough estimate of the separation of the atoms in the

    Streamlines and Fluid Flow

    (Please refer to the attachment) Streamlines represent the path of the flow of a fluid. You can imagine that they represent a time-exposure photograph that shows the paths of small particles carried by the flowing fluid. The figure (see attachment) shows streamlines for the flow of an incompressible fluid in a tapered pipe of

    Line Spectra and the Bohr Model of a Hydrogen Atom

    A singly ionized helium atom is in the ground state. It absorbs energy and makes a transition to the n = 3 excited state. The ion returns to the ground state by emitting two photons. What are their wavelengths? (lowest energy photon) (highest energy photon) Any help is greatly appreciated and thank you!