Molecule Definition and 462 Threads

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge.
In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.
In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. This violates the definition that a molecule contain two or more atoms, since the noble gases are individual atoms.A molecule may be homonuclear, that is, it consists of atoms of one chemical element, as with two atoms in the oxygen molecule (O2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H2O).
Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are typically not considered single molecules.Molecules as components of matter are common. They also make up most of the oceans and atmosphere. Most organic substances are molecules. The substances of life are molecules, e.g. proteins, the amino acids they are made of, the nucleic acids (DNA & RNA), sugars, carbohydrates, fats, and vitamins. The nutrient minerals ordinarily are not molecules, e.g. iron sulfate.
However, the majority of familiar solid substances on Earth are not made of molecules. These include all of the minerals that make up the substance of the Earth, soil, dirt, sand, clay, pebbles, rocks, boulders, bedrock, the molten interior, and the core of the Earth. All of these contain many chemical bonds, but are not made of identifiable molecules.
No typical molecule can be defined for salts nor for covalent crystals, although these are often composed of repeating unit cells that extend either in a plane, e.g. graphene; or three-dimensionally e.g. diamond, quartz, sodium chloride. The theme of repeated unit-cellular-structure also holds for most metals which are condensed phases with metallic bonding. Thus solid metals are not made of molecules.
In glasses, which are solids that exist in a vitreous disordered state, the atoms are held together by chemical bonds with no presence of any definable molecule, nor any of the regularity of repeating unit-cellular-structure that characterizes salts, covalent crystals, and metals.

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  1. C

    [PChem] Maxwell-Boltzmann Molecule Mean Speed

    Hi, I am having trouble with this concept... "A mean speed (c) is calculated by multiplying each speed by the fraction of molecules that have that speed, and then adding all the products together. When the speed varies over a continuous range, the sum is replaced by an integral. To employ...
  2. L

    Finding the dipole moment of a molecule in an electric field

    Homework Statement "A molecule has its dipole moment aligned with a 1.8 kN/C electric field. If it takes 3.5x10^(-27) J to reverse the molecule's orientation, what is its dipole moment?" Homework Equations Potential energy of dipole in an electric field U = -p*E = -p*E*cos(theta) U...
  3. Jackson Lee

    There is little molecule bond between gas molecules, then why we have

    Hey, guys, I have just watced a fantastic animation of the microscopic process of sound wave traveling, in which model was described as many balls connected by springs. But the problem is what we learned in thermodynamics chapter is that there is no bonds between molecules in gas, then how...
  4. P

    Chemistry Calculate persistence length of a single dsDNA molecule

    Hello! 1. The problem statement and all variables AIM: Calculating persistence length P of a single dsDNA molecule from a data set of force F (to the molecule) vs. extension x measurements. Experimental background: pN forces were applied to a single dsDNA molecule spanned between two...
  5. A

    Chemistry Resonance Structures for a Certain Molecule

    Here attached is a question from my exam. My TA removed 1 point out of 7 for a reason. Can anyone decipher for what? There's the writing in red but it is illegible to me. I don't understand to what he refers by 8 and 6 t or +, or whatever he wrote. http://imgur.com/igpyp8V Or can anyone write...
  6. H

    Force exerted by one molecule on container wall

    I came across this problem in University Physics: (a) Oxygen 1O22 has a molar mass of 32.0 g>mol. What is the average translational kinetic energy of an oxygen molecule at a temperature of 300 K? (b) What is the average value of the square of its speed? (c) What is the root-mean-square speed...
  7. J

    MHB Finding the approximate diameter of an oil molecule

    How do you solve a question like this ? :you can obtain a rough estimate of the following simple experiment-let a droplet of oil spread out on a fairly large but smooth water surface .the resulting oil slick that forms On the surface of the water will be approximately one molecule thick. Given...
  8. K

    Exploring Bond Energy & MO Theory in He2 Molecule Formation

    This is a question in "Chemical Principles, 6th Edition, Steven Zumdahl": Bond energy has been defined in the text as the amount of energy required to break a chemical bond, so we have come to think of the addition of energy as breaking bonds. However, in some cases the addition of energy can...
  9. M

    Possible to see a water molecule?

    Are there ANY possible photographic or other types of images of a water molecule? Or are they simply too small to get an image of? Thank you.
  10. W

    Measuring the electron mobility of a molecule

    Hello PF Let's say I have a device with three layers, A, B, and C, where layers A and C are the anode and cathode. I can measure the IV curves from that device easily. Now let's say I added a fourth layer, D, in between A and B. Layer D interacts with layer B such that it increases it's...
  11. A

    Solving an Energy Problem: Calculating Average Molecule Energy Through a Hole

    Hello everyone. I was hoping someone could help me out with the following problem. I tried working it out, but I don't know if I did it correctly or if I missed an important point. It just seems too "short". it would be much appreciated if someone could go through my solution quickly and give...
  12. Hardik Batra

    Kinetic energy of molecule depends upon?

    Average kinetic energy of a molecule is = (3/2)kT Avg. K.E is directly proportional to temp.(T) only. As you increase temp of gas then K.E will also increase. In my book given that, Average K.E is independent of pressure, Volume or nature of the gas. When you increase the pressure...
  13. Hardik Batra

    Kinetic energy and heat energy of molecule?

    I know that . Average kinetic energy of a molecule is (f/2)kT (for translational motion.where f=3 ) In my textbook given that... If the degree of freedom of the gas molecule is f then the average heat energy of each molecule of the gas is = E(avg.) = (f/2)kT which is same as the...
  14. L

    Chemistry Name Molecule: 2-Butanol Naming and Diagrams for Homework Solution

    Homework Statement I have to name the particular molecule that i am looking at and fill in the blanks with that name.Homework Equations Choose from: 2-methoxybutane, 3-butene, 1-butene, butanal, 2-chlorobutane, ethylmethyl ether, butylmethyl ether, or 2-butanoneThe Attempt at a Solution The...
  15. D

    Understanding Feynman's Approach to Covalent Bonding in Hydrogen Molecule

    In his lectures on quantum mechanics, Feynman treats the hydrogen molecule as a two-state system to give a general understanding of the covalent bond. He starts with base state |1> as electron a in ground state of left proton and electron b in ground state of right proton and base state |2> as...
  16. D

    Chemistry Functional group in aspartame molecule

    Homework Statement which functional group is present in aspatame molecule? Homework Equations The Attempt at a Solution why the carbonyl group COO- is not present in the diagram? I can find it in the diagram
  17. K

    HPLC regarding the pore size vs the molecule size

    Hi I have a simple question about HPLC regarding the pore size vs the molecule size of the analyte. Are there cases when it is desirable to have a pore size smaller than the analyte molecule size? In this case, the analyte will be eluted first, then the solvent will be eluted later...
  18. J

    Angular velocity of an oxygen molecule.

    Homework Statement The atoms in the oxygen molecule [O][/2] may be considered to be point masses separated by a distance of 1.2 x 10^-10 m. The molecular speed of an oxygen molecule at s.t.p. is 460 m/s. Given that the rotational kinetic energy of the molecule is two-thirds the of its...
  19. A

    Chemistry Resonance Structures for a Certain Molecule

    Please look at the pictures. I do not understand why they have not included the resonance structure for that molecule for which all the double bonds are displaced is not included.
  20. K

    Calculate the mass defect of a molecule without empirical mass

    Hello, I'm currently writing a chemistry program. The user can create any kind of atom he can imagine, and then combine them into molecules. To properly calculate all the energies involved I need a formula to calculate the mass defect of a nucleus. I mustn't use empirical data to allow for...
  21. S

    Vibrating molecule of IBr - energies

    Homework Statement Effective potential of atoms in molecule of IBr can be described as ##V(r)=V_0[(\frac{r}{a})^{-8}-10(\frac{r}{a})^{-4}]##, where ##a=1nm## and ##V_0=0.1eV##. Calculate the first three vibration states if the potential close to minimum is harmonic. ##M(I)=127g/mol## and...
  22. S

    How Does NaCl Molecule Transition Influence Photon Frequency?

    Homework Statement A molecule of NaCl has a reflective potential ##C/r^n##, where ##n=35##. What is the frequency of radiated photon at oscillating transition of the distance between the atoms is ##r_0=0.236nm##. And what is the frequency if the transition is rotational?Homework Equations...
  23. Runei

    What causes the repulsive force in diatomic molecules?

    Hello, I'm working here with a model for a diatomic molecule. The potential is modeled as two finite wells. For a given distance between the wells, the energy of the ground state will be minimized. If you move the "atoms" closer to each other, the energy rises, and if you move them away from...
  24. Conservation

    Sigma and Pi Bonds for Diatomic Oxygen Molecule

    According to the Molecular orbital theory, diatomic oxygen should have σ2px (internuclear axis) and \pi2py and \pi2pz orbitals filled with two unpaired electrons, one at antibonding \pi2py and the other at antibonding \pi2pz. And of course, the 2s bonding and antibonding orbitals as well...
  25. S

    Is 1-butanol molecule a surfactant?

    Is 1-butanol molecule a surfactant?
  26. K

    What is the difference between a compound and a molecule?

    I have read several definitions that basically say a molecule is formed when two or more atoms join together chemically. And a compound is a molecule that contains at least two different types of atoms. All compounds are molecules but not all molecules are compounds. Examples of molecules...
  27. F

    Detecting the THC molecule in room air

    Is there a material or chemical substance that would have a visable change of any kind when exposed to THC? For example-something I can put in a room and detect if anyone is smoking pot in that area?
  28. Q

    Chemistry Bigger the molecule the more polarizable

    Homework Statement Which is less polarizable in each of the following groups? 1) H2CCH2 or H3CCH3 2) CH4 or C2H6 3) Na+ or Na 4) Sb3- or S2- Homework Equations Polarizability is affected by the number of electrons, the distance of the electrons from the nuclear charge, and molecular...
  29. R

    Moment of Inertia of a molecule of collinear atoms

    Homework Statement Landau&Lifshitz Vol. Mechanics, p101 Q1Find the moment of inertia of a molecule of collinear atoms Homework Equations The Attempt at a Solution I defined the origin alone the orientation of the molecule. I_3=0 obviously. For I_2 I wrote I_2=Ʃm_b[x_b-\frac{Ʃm_a x_a}{μ}]^2...
  30. N

    Normal Modes of a Triangle Shaped Molecule

    Homework Statement A molecule consists of three identical atoms located at the vertices of a 45 degree right triangle. Each pair of atoms interacts by an effective spring potential, with all spring constants equal to k. Consider only planar motion of this molecule. What are 6 normal modes and...
  31. L

    Finding quantum number n of molecule

    Homework Statement A nitrogen molecule (N2) has a mass of 4.68 x 10-26 kg. It is confined to a onedimensional box of length L = 100 nm. What is the approximate quantum number n of the molecule if it has a kinetic energy equal to the thermal energy kBT at room temperature? What is n if it has a...
  32. S

    Direction of vibration of molecule with respect to transfer of heat

    the heat causes the molecule to vibrate.how does the molecule vibrate in terms of angle formed by vibrating molecule and the direction of tranfer of heat in conduction, convention and radiation?
  33. A

    What is the difference between bulk, cluster, and molecule in material science?

    I often find those terms when dealing with material science but I can't teel precisely the difference or the definition of which of these terms. Can anyone help me?
  34. M

    Finding velocity of gas molecule

    Equations: 1. vrms = √(3RT/M) 2. PV = nRT 3.M = mNA I want to answer part a. I am given T,P, and the density of gas molecules (d). From equation 3. I want to solve for m. m = dV = d(nRT/P) m[NA] = M = d(nRT/P)[NA] = dNRT/P; N = nNA. From equation 1. vrms = √(3RTP/(dNRT)) =...
  35. C

    Partition Function For a Single Molecule

    Homework Statement Polymers, such as rubberbands, are made of very long molecules, usually tangled up in a configuration that has lots of entropy. As a very crude example of a rubber band, consider a chain of N molecules which we call links, each of length l. Imagine that each link has only...
  36. G

    Wave function of bonding orbital of Hydrogen molecule

    Hi I am currently looking for the wavefunction of the bonding orbital of the hydrogen molecule. Does anybody here know how this one might look like? So, since there is no complete analytical solution for the Hydrogen atom Schrödinger equation, I am currently looking for approximations of this...
  37. M

    Polarizability if a molecule in raman scattering

    Hello. I'm reviewing background information on Raman scattering and I've noticed that the polarizability scales with v+1 for Stokes transitions and v for anti-Stokes. Why is this and what assumptions are used in the derivation? An explanation or pointing me to a good reference would be...
  38. A

    Chemistry Why Is Ethylene Planar?

    Homework Statement I just had my textbook tell me ethylene is a planar molecule. Not wanting to regurgigate crammed information, I'm trying to understand why the molecule has to be planar. Why can't two hydrogen atons located on one side be oriented in a perpendicular way to the two other...
  39. I

    Is an ionic compound the same as a molecule?

    A little clarification on the two... Would you agree with the text of the following two screenshots? (I highlighted the relevant parts in red) Most important is, screenshot 1 so please address it first: But also curious is, screenshot 2: Are these accurate? Would something...
  40. B

    Chemistry Most likely carbons for nucleophilic attack on a molecule

    Homework Statement I've attached a picture of the molecule. The question: at which molecules (s) would it be likely that there would be a nucleophilic attack? Homework Equations The Attempt at a Solution The answer key says a and c, only. However, I think that b is nucleophilic because the...
  41. M

    What is the relationship between particle velocity and sound waves in air?

    I have an air molecule moving because of a sound wave. f of sound wave = 500 Hz wavelength of sound wave = 0.68 m How fast is the air molecule moving in its equilibrium position? Is it in equilibrium at V max? Would this be where the position = 0?
  42. C

    Chemistry Why is the bond angle 109 degrees in the antidote molecule?

    Homework Statement Please refer to the image Why is y 109 degrees?(given by my teacher) Homework Equations None. The Attempt at a Solution There are four atoms around the carbon atom, I assumed it to be tetrahedral. Why is that wrong?
  43. T

    How can I find the denaturing/breaking temperature of a molecule?

    So essentially, I'm trying to find the temperature at which growth hormone (GH) denatures. I've got a box of it and it says "refrigerate at between 2'C to 9'C". I'm keeping it at room temperature (it's not for use atm), but would like to find out how to know at what temperature GH would break...
  44. E

    How to get N2 molecule orbital theoretically

    How to get N2 molecule orbital theoretically with quantum chemistry program like GAUSSIAN !for example, how to get the picture attached? Thank you!
  45. L

    Does the concept of dipole moment of charged molecule exist or not?

    Generally the concept of dipole moment is used in neutral system, ie the total positive charge equals to the total negtive charge. Could the concept and also the calculation be used in charged system? For example, NaOH, (Na+)(O-2)(H+), we can calculate its dipole moment. Could I calculate...
  46. H

    Difference between bi and bis as prefixes of a molecule?

    What is the difference? I know about di and bi but not about bi and bis.
  47. D

    Solving the Hydrogen Molecule computationally

    Hi, I'm interested in solving the Hydrogen Molecule for a school project (computational physics course) WITH electron interactions included. I'm thinking of calculating the bond length using some kind of variational method, but I'd also like to calculate the energy levels of the two-electron...
  48. Sneakatone

    Need help finding center of mass of a molecule.

    Figure below shows the shape of a nitric acid (HNO3)molecule and its dimensions. Treating the atoms as particles, findthe center of mass of this molecule. a)I know that xcm=m1x1+m2x1+.../Total mass. The total mass in this case is 63 but based on the picture I don't know which mass I should...
  49. Q

    Is 2-Methyl-1-Propene the Correct Naming for this Molecule?

    I've attached the image. Is the naming of this molecule correct? If so, why is the methyl prefix necessary? The three carbon chain + the double bond makes it 1-propene... If not, would the correct name be methylethene?
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