What is Atoms: Definition and 876 Discussions

An atom is the smallest unit of ordinary matter that forms a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across. They are so small that accurately predicting their behavior using classical physics—as if they were tennis balls, for example—is not possible due to quantum effects.
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively – such atoms are called ions.
The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by the nuclear force. This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements. This is a form of nuclear decay.
The number of protons in the nucleus is the atomic number and it defines to which chemical element the atom belongs. For example, any atom that contains 29 protons is copper. The number of neutrons defines the isotope of the element. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature. Chemistry is the discipline that studies these changes.

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  1. N

    Calculate The Distance Where Atoms Start to Repel Each other

    Is there a way to calculate how close two atoms can get before their electrons start to repel each other and prevent atoms from getting closer together. I'm guessing this is dependent on the size of the atom and it's number of protons and electrons. I am asking because I am working on a...
  2. P

    Thermal motion of graphite atoms

    Hi everyone, I've been thinking about the quantum pencil, and I can't quite convince myself that you could perfectly balance a perfectly sharpened pencil even if the uncertainty principle went away. For those who are unfamiliar with the problem, you can read about it here...
  3. N

    Resting masses of isolated neutrons versus neutrons in atoms

    I'm a high school student reading through a book on the discovery of the Higgs boson, and, among several other things, there's one part that I don't understand completely. I understand that the Higgs field is what gives mass to lots of particles that would otherwise be the same without the...
  4. S

    Would an idea be a particle or a wave or both?

    If an Atom doesn't decide if it will be a particle or a wave until it is measured, and we assume thought is the tool for measurement...In quantum physics would an idea be a particle or a wave or both?
  5. desta41

    Vibrational frequency of electrons in atoms

    Below is a paragraph taken from the web site, physicsclassroom.com: 'It is often useful to think of these electrons as being attached to the atoms by springs. The electrons and their attached springs have a tendency to vibrate at specific frequencies. Similar to a tuning fork or even a musical...
  6. D

    Gravitational attraction between two atoms

    The question: Is there a gravitational attraction between two atoms if they are located at a distance of several light years of each other? Or physics does not have the answer to this question yet? ) (Sorry if this question has already been discussed on the forum. Please send a link to the topic...
  7. itssilva

    Math for identifying bosonic atoms

    (And fermionic atoms, as well). Knowing the weird statement that rubidium atoms and such are bosons and reading some of the threads, I've convinced myself that it is a perfectly acceptable possibility; however, I'm not so sure if I learned how to point my finger and say atom X is a...
  8. 1

    Use FMM or FFT for low-discrepancy sample of atoms?

    To complete my Master's thesis, I am working on a problem that deals with an arrangement of initial atoms, and their positions are then changed according to a pseudo-random number generator with low discrepancy. My advisor told me that instead of computing the interactions between the atoms for...
  9. S

    Electronic Transition of Atoms

    Suppose we have an isolated H atom. We are looking its electronic transition. If we plot the intensity of the radiation vs frequency then what will be the nature of the curve and why??
  10. Sachin Vaidya

    Atoms emitted from a tube (Atomic Oven)

    Homework Statement Consider a evacuated long metal tube of length 'l' and diameter 'd' containing a metal source at one end. The metal source is connected to an oven and emits gaseous metal atoms in all possible directions. If an atom hits the walls of the tube, it will get stuck and will not...
  11. S

    Atoms as spheres in packing fraction of crystal lattice

    Why are atoms taken to be spheres, and not of some other shape, in the calculation of the packing fraction of different crystal lattices? In other words, what experimental evidence and theoretical reasoning motivates this form of the atomic shape?
  12. B

    VSCPT and recoil limit on temperature

    I have read that it is possible to go under recoil temperature limit using VSCPT (Velocity Selective Coherent Population Trapping) and that this method is based on atoms trapping in quantum state in which they can't absorb light. I have found same papers but they are too detailed for my...
  13. J

    Length generated by all atoms contained in 1 gram of iron

    Hi, I tried to calculate the distance resulting from Na iron atoms contained in 1 g. scaled in meters and by juxtaposing them in a single thread (segment). I did the following calculation with: Atomic radius : 140 E-10 meters Na : 6 E23 atoms in 56 g. of iron => ( 2 x 140 E-10 x 6 E23 )/56...
  14. R

    Questions about atoms: shells, attraction, elements

    My understanding is the atomic model has electrons occupying shells and in particular numbers, but what's known about why they arrange themselves into shells and in those particular numbers? The teaching is that electrons have a negative charge and protons have a positive charge - but why do...
  15. Stephanus

    Are neutrinos much more abundant than atoms?

    Dear PF Forum, I once read in several links just a couple of days ago, that the number of neutrinos exceeds the number of baryon in the universe by several orders of magnitude. 1. Is that true, that neutrinos are much more abundant than atoms? 2. Do neutrinos have mass? Not that they are...
  16. VoteSaxon

    Fraction of thermally excited atoms

    Homework Statement There is an electronic transition between the first energy state and the ground state of a neon atom, emitting a wavelength of 746nm. The question asks for the energy of the transition and an estimate of the fraction of atoms in a sample that is thermally excited at 300K...
  17. P

    Is this a eureka moment? .how do we know atoms exist?

    just picture what happens when you fill a 2 liter soda bottle with water (or any liquid) and try to pour it all out at once. it comes out in clumps. This means there will be competition, since all the water will try to escape all at once. the fact that there is competition means that there...
  18. D

    The Mystery Behind Atoms Vibrating & Sound Creation

    Hi Likely a stupid question. If atoms vibrate with heat, why don't hot objects make a sound, i.e transferring vibrations to the surround atoms (air) into our eardrums? They vibrate on ultra-infra sound? Or it's a extremely weak sound? or this is not the same vibration as the cause for sound? or...
  19. Jilang

    How is quantum interference achieved with atoms fired from opposite directions?

    I came across this today, but wasn't quite sure how it worked. http://www.sciencedaily.com/releases/2015/04/150409081436.htm Are the two atoms fired from opposite directions?
  20. J

    Exploring Possibilities of Bonding Fleeting Heavy Atoms

    I read about scientists creating new heavy elements such 117 and that the properties of such exotic elements are mostly unknown because the scientist have just microseconds before they decay. Would it be at all possible to bond some new molecule with the heavy atom and some other appropriate...
  21. AdityaDev

    Structure of 1s and 2s orbitals

    From the ψ2 vs r graph (i.e probability of finding an electron vs distance from nucleus graph), there are no nodes for 1s orbital while there is a node in the 2s orbital graph.But they have similar structures right? Then why is there a difference in finding the probability of finding an...
  22. bohm2

    How to entangle nearly 3000 atoms using a single photon

    Entanglement with negative Wigner function of almost 3,000 atoms heralded by one photon...
  23. eis3nheim

    Atoms and energy levels question

    As the atoms of a material are brought closer together to form the crystal lattice structure, there is an interaction between atoms, which will result in the electrons of a particular shell of an atom having slightly different energy levels from electrons in the same orbit of an adjoining atom...
  24. Shri13

    Photonic vacuum and atomic stability

    Hi friends, this is my third post of my curiosity. :woot: First of all a photonic vacuum (as defined by me) is a region of space where there doesn't exist any type of photons or EM radiations ( those too which are beyond the detection of our present tech... i.e. including each and every...
  25. Calpalned

    Two atoms of an element with a half life of ten years

    On the other hand, what if we only have two atoms of an element with a half life of ten years. Then after then years, only one atom of that original element remains. What happens next? Is the lone surviving atom immutable?
  26. C

    Uncovering the Mysteries of Photons: Energy, Illumination, and Mass - FAQs

    1) Do photons eventually run out of energy and stop producing light? 2) If atoms are non-solid and more than 99% empty space, what is the photon illuminating when it hits a surface? 3) What is the actual light being produced, as opposed to the photon producing it? 4) is it possible for a Higgs...
  27. akashpandey

    Are Atoms Alive? Understanding the Building Blocks of Life

    We are made up of atom & we are alive But a pen is also made up of atom but it is not alive
  28. A

    Fermi energy in metals approximately doubling

    Between Cs and Na, the fermi energy in metal approximately doubles. why doesn't the carrier concentration also double?
  29. G

    Why reduced atoms are more energetic?

    For example, in glycolysis, NAD+ is reduced to NADH and then it's more energetic. Why adding electrons to an atom gives it more energy?
  30. S

    Two Ag atoms in magnetic field

    Homework Statement Two Ag atoms wits spin ##s=1/2## are at ##t=0## in state ##|\uparrow >|\uparrow >##. The first atom is in homogeneous magnetic field in ##y## direction while the second atom is in homogeneous magnetic field in ##z## direction. The strength of the two magnetic fields are the...
  31. K

    Notation on energy level for atoms

    Hi there, I am reading an introduction for atomic physics. In one section, it introduces the energy levels for Rubidium and there are some labels like F=1, F=2 etc. shown next to the fine structure of a level . Also refer to...
  32. A

    How to Calculate Energy for Atmospheric Molecule Reaction and Isolate Gases?

    The atmosphere consists of two toxic, and unfortunately abundant gases in our atmosphere. Carbon dioxide and methane. Carbon dioxide produced by factories are not needed in the atmosphere and cause harm. So is methane. Acegikmoqsuwy and I thought of an equation to solve this problem: CH4 + CO2...
  33. T

    Quantum Computing with Zero Spin Atoms?

    Hello, Is it possible to build a qubit from an atom with a nuclear spin of zero (ie. 16O, 12C, 32S)? Would it depend on electron spin instead? Thanks!
  34. N

    Why Carbon Supports Life: Exploring Atomically-Based Lifeforms

    I'd like to understand more about how/why carbon-based life comes about. All things are atomically based, why is it that carbon atoms/elements are able to sustain life better than any other element? Thank you
  35. N

    Psi Epistemicism & the Reality of Particles & Atoms

    For those of you who have read the theorem, probably have also read Matt Leifer's review of it. In his review he says that the only way to remain psi epistemic is to be an anti realist(copenhagen), or to abandon the bell frame work. Is it viable to be psi epistemic but still believe that...
  36. N

    What are the atoms floating in space

    Atoms are all around us, right? we cannot move without interacting with atoms in the air the ground et cetera. This got me thinking about how infinite and vast space is compared to the seemingly small amount of planets, which are full of atoms. I use to think that planets were where all the...
  37. P

    Gravity affect on the motion of atoms ?

    I was wondering if the run away gravity in a super massive black hole could cause a lock up of sorts, and stop (nearly) all atomic movement? Packing the matter at it's core so tightly, that it would paralyze it at an atomic level. Could this possibly mean that near the center of these monsters...
  38. N

    Every known element has a unique atom?

    This notion perplexes me. Could I please have this explain with an example(s). I am confused are atoms not made up of the same protons and neutrons which are just essentially negatively or positively charged particles which are made of quarks? Which as confusing as that can become. How can one...
  39. T

    Fusion Due to Gravitation in Bosonic Atoms

    In a bosonic atom i.e. Hydrogen, why do we never observe quantum tunneling past the coulomb barrier leading to multiple atoms occupying the same area of space thus (due to Newton's law of universal gravitation) accelerating towards each other resulting in nuclear fusion?
  40. V

    Resonance in electron impact on atoms

    Can someone please explain the significance of resonance levels that forms when electron collides with atoms. How this resonance levels are different from other levels ?
  41. M

    Why Do g Factors Vary Among Different Atoms?

    Hi, last week I read Rabi's paper "The Molcular Beam Resonance Method". This paper contains the basic idea of the oscillation which we call "Rabi Oscillation" as many of you guys know. However, at the end of this paper, Rabi calculates nuclear magnetic moments of Li (atomic mass 6), Li (atomic...
  42. O

    Calculating Emitted Photon Properties for Excited Atoms | Homework Help

    Homework Statement Atoms of a certain material are in an excited state 1.8eV above the ground state and remains in that excited state for 2.0ms before to the ground state. Find 1) The frequency of the emitted photon 2) The wavelength of the emitted photon 3)The uncertainty in the energy of the...
  43. R

    Understanding Time Dilation: Exploring the Effects of Speed on Time

    A question about time dilation.. I find myself in an argument / discussion about the theory of time dilation, and it seems to me, that the terminology is really the problem. Would it not be more accurate to say that the effects of time slow, as speed increases ? To say that our test of clocks...
  44. C

    Calculating Minimum Energy for Gamma-Ray Displacement of Carbon Atoms

    Hi everyone, For one of my PhD project I am trying to calculate the minimum energy required to displace a carbon atoms with gamma rays. Knowing the displacement energy (Ed) for C in diamond (30 -40 eV), I've managed to calculate the minimum energy required using electron with the formula...
  45. L

    Kinetic Enegry and Hydrogen Atoms

    Homework Statement (a) What is the minimum kinetic energy in electron volts that an electron must have to be able to ionize a hydrogen atom (that is, remove the electron from being bound to the proton)? Answer: 13.6 eV (b) If electrons of energy 12.8 eV are incident on a gas of hydrogen...
  46. Razorvox

    How are atoms combined with the body?

    EDIT: "In what fashion are atoms or molecules added to a body, then attached, how exactly do they get replaced?" http://imgur.com/pmR8RB9 (I realize atoms are much smaller) Sorry for the crudity of my drawing but I think you get the general idea. I can't picture what happens? I believe they...
  47. L

    The Space Between Atoms -- Teaching Middle School

    Hi guys, I know that if we consider a basic atomic model ( not considering quantum mechanics here) that an atom is mostly empty space ( 99.99999%) or something like that. But how about the space between the atoms? Would it be appropriate to tell middle school students...8th graders... that...
  48. K

    Is a positive charge attracted to the electrons around atoms?

    An atom has an equal amount of positive and negative charges. But those charges are not all in exactly the same spot. Electrons are closer to other atoms than the protons are. So, would a lone positive charge be attracted towards the electrons in an atom?
  49. C

    Difference between fusion and fission

    Hi there, Sorry if thisis a stupid question its just been bugging me for a while and I am not a scientist as such so need help with the answer... nuclear fission is where two atoms collide and release energy yes? nuclear fusion is where two atoms combine to release energy and a new isotope...
  50. W

    Relating molecules, atoms to number of optical branches (modes)

    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...
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