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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.

Mean Free Path & Surplus uranium produced

(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 fuel rods in a PWR? (Please

What is an atom Exercise Sheet

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

Fermi energy for a gas of electrons.

Sample of question (Please refer to attached PDF document for full details): We have at our disposal an amount of energy equaling 3.5kJ and we wish to allocate 1 mole of gas which occupies volume V.

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

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

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

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

COAL ENERGY

Coal is combusted in a steam boiler. The specific coal contains 25 MJ/kg If the boiler is 90% efficient, how much coal must be burned per hour to produce a stream thermal gain of 665 MJ/s. Roughly how much CO2 will be produced by this boiler?

Writing Matrix Equations and Programs for Spring Mass System

13. Consider the spring mass system (see attached file) (a simple model of a short polymer molecule). The blocks are free to move but only along the x-axis. The springs connecting adjacent blocks have spring constant k1, while the two outer springs have stiffness k2. All the springs have a rest length of one. (a) Write the matri

States of atoms

A water molecule can vibrate in various ways, but the easiest type of vibration to excite is the "flexing" mode in which the hydrogen atoms move toward and away from each other by the HO bonds do not stretch. The oscillations of this mode are approximately harmonic, with a frequency of 4.8 x 10^13 Hz. As for any quantum harm

Distance Between Particles and Energy in Positronium

Positronium is an atom composed of an electron and a positron (mp = me, Q = +e). Calculate the distance between the particles and the energy of the lowest energy state of positronium. Hint: the reduced mass µ of the two particles equals me/(1 + me/m). -----------------a0 ------------------E0

Elastic Collision of two atoms in two dimensions

Please help me solve the following: An atom of mass m moving in the x direction with speed v collides elastically with an atom of mass 3m at rest. After the collision, the first atom moves in the y direction. Find the direction of motion of the second atom and the speeds of both atoms (in terms of v) after the collision. ---

Root-mean-square speed

What is the root-mean-square speed of chlorine gas molecules at a temperature of 47 degrees C? (Molecular mass of Cl2 = 71)

Nuclear Energy and Elementary Particles

1.) It has been estimated that the Earth contains 1.0 x 10^9 tons of natural uranium that can be mined economically. If all the world's energy needs (7.0 x 10^12 J/s) were supplied by 235(U) fission, how long would this supply last? Assume that the average energy released in a fission event is 208 MeV. (Hint: 235/92(U) has a per

Free Electron Theory

(a) (i) What are the main assumptions of the free electron model? (ii) Give an example where the free electron model is in good agreement with experiment. (iii) Give an example where the free electron model fails. (b) (i) How does the nearly free electron model improve on the free electron model? (ii) Describe one of the s

Problems of General Conceptual Physics

PROBLEM: A cylinder container has a couple of holes punched into the bottom of it and the water is spurting out the holes due to the water pressure. You drop the water filled cylinder and as it is free falling the water no longer spurts out the holes. What happens to g, and hence weight, and hence weight density, and hence

Order of Magnitude Calculations

Legend has it that, many centuries ago, Archimedes jumped out of his bathtub and ran across town naked screaming "Eureka!" after he solved an especially difficult problem. Though you may not have thought of things this way before, when you drink a glass of water, the water that you are drinking contains some water molecules that

Atomic States

(See attached file for full problem description) --- Atoms of lithium are able to absorb photons of frequency 2.01 x 1014 Hz. This corresponds to a transition state from the ground state (at -5.37 ev) to an excited state. Zero energy corresponds to the state in which one electron is completely removed from the atom. (Use

Thermal expansion:

A solid steel plate with a hole through its center, drops in temperature, what will the hole's diameter do?

Moles of Gold and water

When you compare one mole of gold to one mole of water what will they have in common (same mass, volume or number of molecules)?