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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

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

"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

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

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

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

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

Physics Problems

How does the number of atoms in a 26.5 gram gold ring compare to the number in a silver ring of the same mass? Amoung the higest and lowest temperatures recorded are 136degrees F in the Libyan desert and -129Degrees F in the Antarctica. What are these in Celsius? To make a secrue fit, rivets that are larger than the rivit

Solving: Kinetic Theory of Gases

Hi, I need some assistance with the following problems: 1. If the translational rms speed of the water vapor molecules (H2O) in air is 664 m/s, what is the translational rms speed of the carbon dioxide molecules (CO2) in the same air? Both gases are at the same temperature. 2. Near the surface of Venus, the rms speed of c


What kinds of evidence supports the belief that molecules of various kinds, including some complex ones, exist in space? Please include references to support answer.

Calculating force, power, equilibrium, and energy

1. A Ping-Pong ball has a diameter of 3.8 cm and average density of 0.084 g/cm3. What force is required to hold it completely submerged under water? 2. A tank with a cover, containing a liquid of density p, has a hole in its side at the distance y1 from the bottom. The diameter of the hole is small relatively to the diamete

Number of molecules

An expandable chamber contains 16.0 kg of molecular oxygen at STP. How many molecules are in it? How many moles?

Atomic Mass

Question: What is the mass of hydrogen and the mass of oxygen in one liter of water? How many atoms of hydrogen and atoms of oxygen does it contain? What is the mass of one H2O molecule in kilograms?

The Speed of Nitrogen Molecules

The Speed of Nitrogen Molecules The kinetic theory of gases states that the kinetic energy of a gas is directly proportional to the temperature of the gas. A relationship between the microscopic properties of the gas molecules and the macroscopic properties of the gas can be derived using the following assumptions: • The ga

Multiple Choice Questions

1. Nitrogen may be combined with oxygen in proportion by mass of 1.75 g nitrogen to 1.00 g oxygen to form the gas nitrous oxide, N2O. The same elements may be combined in the ratio of 0.438g nitrogen to 1.00g oxygen. What is the atomic composition of the second compound? a. NO(2) b. NO c. N(2)O d. NO(3) 2. I

Molecular Mass, the Mole, and Avagadro's Number

Question: The artificial sweetener NutraSweet is a chemical called aspartame (C14 H18 N2 O5). A) What is its molecular mass (in atomic units)? B)What is the mass (in kg) of an aspartame molecule?


1) Polymers, like rubber, are made of very long molecules, usually tangled up. Another very crude model of a rubber band is that each link is either crumbled up or stretched. If it is crumbled up, its length is negligible and it is in the lowest energy state, call it E = 0. If it is stretched, then its length is L and it is in