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.
The expression relating the mean number of molecules with velocities in the range v and v + dv and position r and r + dr is given by
where n = N/V is the number density of molecules.
My question is: Since LHS is an integer, how do we ascertain the RHS is an integer, since it involves pi and an...
Homework Statement
A container has neon gas in the temperature 273 K. We heat the container to the temperature 373 k, keeping the volume constant. Find the average velocity of the molecules of neon before and after the heat.
Homework Equations
U=3/2vRT
The Attempt at a Solution
I thought to...
If QM is a statistical model to approximate something underlying space time we don't quite understand yet, and there is a complex geometry underlying space time, is it possible to find other ways to simplify molecular optimizations and electron interactions in computational chemistry using...
Homework Statement
Homework Equations
Please see below.
The Attempt at a Solution
I'm probably being really stupid here but how can the number of molecules equal
If we integrate we get a volume multiplied by density, how can that equal a number of particles?
Dear Everyone,
If we have a set of diatomic molecules consisting of a common element (F atom) and the other atoms belong to the same group; which are: BeF, MgF, CaF, SrF, and BaF. We want to study the electronic structure of these molecules by comparing their molecular electronic states. We...
(@mfb posted an article about this here, I think it deserves an own thread, and I did not find one, so I start one :smile:)
The comet-like composition of a protoplanetary disk as revealed by complex cyanides
Karin I. Öberg, Viviana V. Guzmán, Kenji Furuya, Chunhua Qi, Yuri Aikawa, Sean M...
Why is the average kinetic energy of the molecules a cold liquid less?
As the temperature of a liquid decreases, the average kinetic energy of its molecules reduce. What is the reason behind this?
Hello Everyone,
A little question regarding the TDMs between two different electronic states of a diatomic molecule. If I am calculating the TDM from state A to state B, is it the same if we are calculating the TDM from state B to state A? Are these two transitions the same?
Thank you so much...
Hi there!
Is there an online, hopefully free resource (preferably textbook) that details the process of molecular modeling? Specifically, computationally performing geometry optimizations, vibrational analyses, calculating Raman spectra, detailing the theory behind Hartree-Fock, DFT, post-HF...
Homework Statement
According to statistical mechanics, the average kinetic energy of a particle at temperature T is 3kT/2, where k is the Boltzmann constant. What is the average de Broglie wavelength of nitrogen molecules at room temperature?
Homework Equations
KE = 3kt/2 = p2/2m
λ = h / p...
Homework Statement
A mixture of two substances exists on a cubic lattice of N sites, each of which is occupied by either an A molecule or a B molecule. The number of A molecules is NA and the number of B molecules is NB, such that NA + NB = N. The energy of interaction is k_BT\chi_{AA} between...
I would like to understand how LCAO may be used to construct the matrix to be solved for the molecular orbitals of two cases of molecules:
1) small molecules like H3 (or H3+, HF2-, H2O, CH4, etc.
2) groups or parts of molecules with delocalized pi-systems (including linear and cyclic...
Hi everyone!
I am researching on Metals Work functions, and I need a table of distances between molecules! I searched on the web almost a week, but I didn't found at least A table. Please help me! If it is in a book, tell me the name of the book, or tell me where can I find it.
Any help would...
Homework Statement
Estimate the energies of interaction at 25 °C between (i) two hydrogen molecules and (ii) two nitrogen molecules, if each pair is separated by 0.3 nm. Explain fully and clearly your reasoning and any assumptions you make in your answer. State the source of the values of any...
Hi there,
I am a little confused with triplets in magnetic filed and ESR measurements on them.
Triplet levels in aromatic molecules are indexed Tx, Ty and Tz and if magnetic field is applied they start to mix. If magnetic filed is along the x direction of the crystal, then Tx level remains...
Do they unbind somehow? Or are they somehow "eaten" by the receptor, so the more you taste of something, the less of it gets through? I'm only a Wikipedia/Youtube student so my knowledge has weird gaps all over the place. Got thinking about this by noticing an interesting taste that some...
Avogadro's Law states that 'equal volumes of gases at the same temperature and pressure contain the same number of molecules' or moles of gas.
My question is ,will it be correct if we reverse the law,
I mean if gases of equal moles at the same temperature and pressure will have equal volumes,is...
I'm watching a Leonard Susskind video about the Higgs Boson where he gives an example of how an electric field can change the mass of a water molecule. If you put a water molecule between two capacitor plates (so the electric field is uniform and the field lines are parallel), it will tend to...
I just began reading Feynman lectures and it turns out that during evaporation, water molecules that move faster than average (higher temp) break away from the attraction of their neighbors leaving behind molecules that move slower than average (lower temp) and result in a cooler liquid. When a...
Suppose the molecules of an ideal gas move with a speed comparable to the speed of light. I am trying to adapt the kinetic theory to express the pressure of the gas in terms of m and the relativistic energy, but each time I try to derive the expression, I get: P = (1/3)(N/V)(v/c)√(E2 - m2c2)...
Hello !
When we say that we use a 6-31G for a molecule (ex: N2), it is this number of gaussian (6+3+1) for both of the atoms or for each atom ?
Thank you
I read an article about creating molecules from photon, and this part-
As the photons enter the cloud of cold atoms, Lukin said, its energy excites atoms along its path, causing the photon to slow dramatically. As the photon moves through the cloud, that energy is handed off from atom to atom...
Homework Statement
Hi all,
There is a question from the course book:
Homework Equations
S=k_B ln W
The Attempt at a Solution
My solution:
So first of all, for each molecule, there are 2 motions: translational and rotational.
For rotational I get:
W_1 =\Omega \left ( \theta \right )
For...
I want to design a system of some kind that will photodissociate isolated diatomic molecules. I began by looking at Einstein's treatment of absorption and emission rates, molecular orbital geometry, the Morse potential and various other topics. I'm fairly well versed in quantum and E&M (full...
I am working on a project, however I am having trouble finding the right material for it to work. I am looking for a nano-material or any molecule that will emit a radio frequency when subjected to a voltage or a current at around 37 degrees Celsius. I would really appreciate it if someone could...
Homework Statement
I know that temperature is a measure of the kinetic energy of gas molecules. at a given temperature different gases have the same average kinetic energy.
But in solids and liquids there is also potential energy between the close atoms/molecules. how do i know that temperature...
Hi, so I'm a first year neuroscience student at Carelton University in Canada. I had a little bit of a "revelation" with this topic recently after I understood it a bit better and I think this is really interesting. (If I understand it correctly!) We're learning about Kekule structures...
Homework Statement
1. A student investigated several esters, and made octyl acetate, an ester with the fragrance of oranges. The student used the acid derivative, acetyl chloride (as you saw decanedioyl dichloride used to make 6,10 nylon) and 1-octanol. Using the following information...
Homework Statement
Part A: Calculate how many mocules per cubic metre in air at 27°C and at a pressure of 1.1 atm (1atm is 1.01 x 10^5)
Part B: What is mass in grams of 2.4m^3 of this air.
Assume that 75% of the air is N2 (with molar mass of 28 g/mol) and 25% O2 (with molar mass of 32 g/mol)...
I'm stumped as to how many optic branches (modes) are present if there are X number of molecules in a unit cell and Y number of atoms in each molecule.
I know that each individual atom has 3 degrees of freedom and more generally in a single unit cell, there are 3 acoustic branches (modes) and...
I took chemistry a couple years ago but never got a satisfactory answer as to why covalent bonds hold molecules together. I understand that they share their outermost electrons, but why would that keep them together? Do the electrons pull against each other or something?
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...
1. Suppose DNA molecules of a Streptococcus bacterium contain a radioactive isotope N^{15}, if this bacterium is then put in an environment containing only N^{14} and after 5 generations (DNA duplication), how many N^{15} DNA molecules remain ?
Homework Equations
3. after 5...
As I understand, when an electric field is applied to an atom then the nucleus and electron cloud will be shifted out of balance giving rise to an electric dipole moment. Some molecules have permanent dipole moments though,
e.g. Hydrogen Chloride,
". . . when a hydrogen chloride molecule is...
Hello there. I did research on some of Schrodinger work. My question is the transfer of Energy between the Atoms and Molecule. Schrodinger made an analogy with the Cat/Atom Scenario but the real particle in question is the NH2 Mole & H-Atoms with ghost energy being observed. The reason I read...
(1s,4s)-4-(tert-butyl)-1-methylcyclohexan-1-ol
(1r,4r)-4-(tert-butyl)-1-methylcyclohexan-1-ol
These are the two results given by the solution's manual textbook to this question:
Keeping in mind that carbocations have a trigonal planar structure, (a) write a structure for the carbocation...
Hello,
Is there anywhere a reference to get an idea, why wool fat consists of over 200 different molecules?
Is there some sort of a general law or ruling, like the Darwin's evolution, that nature produces nothing more and nothing less as what is required for the propose?
If so, how is...
I read that essential oils can go through the skin. I am told that there are more water molecules in just 10 drops of water than stars in the whole universe, so if they are so tiny, why don't they go through the skin membrane pores, which are perfectly visible under an optical microscope? You...
One of the first things about QM we were taught in my undergraduate physics program is the deBroglie relation:
λ = h/p
Now, it makes sense that that this might hold for all elementary particles, especially since the evidence generally seems to suggest that the commonly observed forms of...
When water is vigorously shaken the kinetic energy and, hence, the motion of the molecules increase. Which particular forms of energy do increase : the translational energy (is this the energy associated with the collision and the chaotic random motion of the water molecules ?) or also the...
Homework Statement
How many water molecule in CuSO4.5H2O attached only by coordinate bond?
The Attempt at a Solution
Copper exists in the form of Cu2+. So, it has one vacant d-orbital. The answer should then be 1. But it's 2 :(
Are species such as sulfuric acid and phosphoric acid better represented as charge-separated species rather than as species with no formal charge on any of the constituent atoms?
Also are the central atoms of trigonal bipyramidal molecules (e.g. phosphorous) hybridized as sp3d2 or do such...
Homework Statement
Part(a): Find rate of incidence of gas molecules.
Part(b): Find v1 and v2.
Part (c): Find mean free path for faster molecules.
Part (d): Find mean free path of 10m/s molecules.
Homework Equations
The Attempt at a Solution
Part (a)
Letting ##\phi## be flux, and ##\Delta...
The number of molecules per cubic metre of air at standard temperature and pressure is about 2.7X10^25 / m^3 . What is the average separation of these molecules?
I know the number of molecules is derived from the equation pv=nRT.But what does average separation of molecules mean and how do i...
It is taught that the classical treatment of the diatomic atom would give a heat capacity of $7/2$ due to 7 degrees of freedom, (three translational momentum, two rotational momentum, on vibration momentum and on vibration position).
This is based on the Hamiltonian looking like:
$$
H =...
Homework Statement
What is the number density, N/V, of gas molecules in the closed vessel in the previous problem?
(Previous problem: A closed vessel contains an ideal gas at an absolute pressure of 1.5 atm and a termperature of 42 degrees celsius. To what final temperature (in °C) must the...
I'm trying to understand how to draw MO diagram for molecules such as CO, HF, and NO. I am finding so much conflicting information on how to order the σ and pi boxes in the diagram. Now, I know that the more electronegative atom's orbitals are going to be lower in energy than the less...