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. B

    Do atoms generally exhibit superposition when not isolated?

    Do atoms "generally" exhibit superposition when not isolated? Do atoms "generally" exhibit superposition when not isolated from the enviorment?I know that electrons and photons do but are regular atoms in the real world "generally" in a state of superposition without all the scientific...
  2. C

    What is the net charge and why does it matter?

    What is electric charge? Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. So, if the particle has electric charge, there is an electric field around it. What is a Neutral particle? In...
  3. W

    Why do atoms have magnetic moments, but no electric dipole moments?

    i do not know why. does the magnetic moment of an atom come only from the spins of the electrons?
  4. M

    Quasiparticles,Plasmons,and exotic atoms

    I'm aware that there are certain unique configurations of atoms often referred to as exotic atoms. One type of these atoms involves the substitution of an electron with a muon in hydrogen. The relatively large mass of the muon results in the size of the hydrogen atom decreasing (which is the...
  5. T

    Can atoms/ ions behave quantum mechanically at biofriendly temperature

    Can atoms/ ions/ molecules behave quantum mechanically at bio-friendly temperature? For example, cells in the human body needs around 37 degree Celsius to function properly. There are however some organisms such as Tardigrade ( which can survive for a few minutes at -273°C and for days at...
  6. I

    Neutron Stars vs Atoms: A Comparison

    So how much denser than is a neutron star than an atom? Is it called a neutron star because electron's orbital effect no longer exists/acts the same, so as to no longer cause 99.99% of everything to be space?
  7. harjot singh

    Polarity in Atoms: Understanding Electron Movement in Covalent Bonds

    here polarity in an atom is although chemistry topic but my problem is related to QM my question is that how electrons revolve around the covalently bonded atom where the electrostatic forces of attraction causes them to stuck at a single point. but if this assumption is wrong then correct me...
  8. bananabandana

    Why, IF electrons really orbited atoms, would they lose energy?

    Homework Statement Why, IF electrons really orbited atoms, would they lose energy? Homework Equations The Attempt at a Solution I realize they're meant to emit light. But why? I understand vaguely that the E field might be changing with time, since you have a changing magnetic flux... but...
  9. A

    Can Atoms Ever Truly Die?

    How does an atoms "life" end? Two stupid questions. What "force" keeps the electrons spinning around the nucleus in an atom, and how does an atom eventually "die", or wear out? Thanks for a serious answer, I really have no idea. :frown:
  10. P

    The number of ways of placing M atoms on the interstices of a lattice

    Hi, N atoms are arranged to lie on a simple cubic crystal lattice. Then M of these atoms are moved from their lattice sites to lie at the interstices of the lattice, that is points which lie centrally between the lattice sites. Assume that the atoms are placed in the interstices in a way...
  11. D

    Spectral Analysis of Gas Atoms: Temperature Calculation

    Hello Homework Statement A gas of atoms, each of mass m, is maintained in a box at temperature T. The atoms emit light which passes (in the x-direction) through a window in the box and can be observed as a spectral line in a spectroscope. A stationary atom would emit light at the sharply...
  12. P

    Quadruple bond between two carbon atoms

    I was wondering if a quadruple bond between two carbon atoms would be possible. I found this on wikipedia about "dicarbon": http://en.wikipedia.org/wiki/Diatomic_carbon, which is related to this question, since what I'm describing is an isomer of dicarbon. Anyone have any ideas?
  13. anorlunda

    Heavy atoms in black hole jets.

    A recent APOD page discussed jets ejected from black holes. It said, "Recent evidence indicates that these jets are composed not only electrons and protons, but also the nuclei of heavy elements such as iron and nickel." What is thought to be the mechanism of production of these heavy nuclei?
  14. 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...
  15. G

    Spectral lines from multiple atoms

    Homework Statement "A gas discharge tube contains H 1 , H2, He 3 , He4, Li6, and Li7 ions and atoms (the superscript is the atomic mass), with the last four ionized so as to have only one electron. (a) As the potential across the tube is raised from zero, which spectral line should appear...
  16. D

    Collision of Atoms: Find Motion & Speeds

    An atom of mass m1 = m moving in the x direction with speed v1 = v collides elastically with an atom of mass m2 = 5m at rest. After the collision the first atom moves in the y direction. Find the direction of motion of the second atom. ________ ° counterclockwise from the +x-axis Find the...
  17. N

    Does the nucleus of atoms of noble gases vibrate and emit E.M wave

    People normally talk of electrons performing oscillatory motion when an electromagnetic field is incident on an atom. But, won't the electric field of the E.M. wave cause the nucleus of the atom to vibrate...? . "Note: Here I am talking of isolated atoms, that is atoms of noble gases, and not...
  18. T

    Making atoms out of their building blocks (p,n,e-)

    Greetings Pfers I am curious what breakthroughs need to be made for the completion of a device capable of forming an atom out of the basic subatomic particles (protons, neutrons and electrons). Technology is advanced enough to where we have machines capable of generating these subatomic...
  19. B

    Potential Energy of Two Atoms?

    Homework Statement The potential energy of two atoms separated by a distance r may be written as: U(r) = 4Uatomic * [(r0/r)12 - (r0/r)6] >Given r0 = 4.0 Ao and Uatomic = -0.012795 eV, what is the distance at which there is no net force between the atoms? Express your answer in terms of...
  20. N

    How many atoms thick is a sheet of paper?

    Well, what do you think? And why do you think what you think?
  21. U

    How many Rb atoms to fit on a 9Cm^2 square?

    1. The problem is in the attachments 2. Basic chemistry knowledge 3. The radius of one Rb atom is 4.95/2 time 10^-8 cm, we calculate the area then divide 9 into the area of one atom, we get the number of atoms, why is 4.7 x 10^15 atoms wrong?
  22. G

    What happens to atoms that havent reacted in a chemical reaction?

    So let`s say that we have a chemical reaction with liquid oxygen and liquid hydrogen, but we`ve got very little hydrogen, and very much oxygen. As we pour these two liquids together they react with on another and create water. However since there was a very much bigger amount of oxygen than...
  23. G

    Why does bringing N 1-orbital atoms together yield N levels?

    A common example of this is that when bringing N hydrogen atoms together into a ring. Far apart, assume each electron exists in the 1s state. As we bring them together, instead of each electron staying at the original 1s level, or all of them changing by the same amount, the 1s level fans out...
  24. V

    Can We See Atoms and Molecules Without High Powered Microscopes?

    Hi guys, I hope you don't mind me posting here, I am doing some research into atoms, molecules and microscopes. I have no knowledge of physics, the quantum world or microscopy so if my questions seem silly, please look past that and help me. Thank you I have two questions. Is there a way...
  25. J

    How do atoms move through space?

    Hi, I'm sorry if I've hit the wrong subforum. Although physics is not my strong side this question has been puzzling me for some time now and from I've read so far - there's no clear answer yet. Here's the question: If we take an atom and mark it's position in space at time X and then it's...
  26. M

    How do atoms with low energy orbitals posses high energy electrons?

    In the case of an atom of Cesium ejecting an electron, it would lose one electron from the 6s orbital. The 6s orbital is very high in energy and similarly so would the electron that is ejected from it, right? So if there was a Nitrogen atom as well, how would it be possible that the Nitrogen...
  27. N

    Calculating Number of Oxygen Atoms in CaSO4: A Pop Quiz Challenge

    I had a multiple choice problem on my pop quiz. How many oxygen atoms are there in .00334 grams of CaS04 X 2H2O. The molar mass is 172 g/mol. So .00334/172 = 1.9 x 10-5 moles x 6 since there are 6 oxygen x 6.022 x 1023 = 7.016 x 1019. None of the answer choices had that. Did I do it wrong...
  28. Islam Hassan

    Do Elementary Particles Jiggle Like Atoms?

    Do Elementary Particles "Jiggle" Like Atoms? Like the question says, if atoms jiggle about because their constituent sub-atomic particles are moving within the atom, is this movement simple orbital/linear displacement or is there also a "jiggling" to it? If there is a "jiggle" or vibration...
  29. G

    Covalent bond of 2 or more atoms?

    I am not in Atomic physics, Everywhere is the standard picture of a bond with 2 atoms sharing 2 electrons. Why is it not possible to share 3 or more electrons that it would form something like a tetrahedron (see attachment)
  30. leviterande

    Are all atoms of a ferro conductor attracted in a magnetic field?

    That is what I wondering. When you put a ferromagnetic conductor in a strong magnetic field, the ferro conductor is strongly attracted because of induced strong magnetic dipole moments inside the conductor. My question: are all or (atleast a large portion) of the atoms of the conductor...
  31. R

    Finding number of atoms per cm^3 of zinc?

    Homework Statement Zinc has a density of 7.17 Mg/m^3. Calculate (a) the number of Zn atoms per cm^3, (b) the mass of a single Zn atom and (c) the atomic volume of Zn. Homework Equations atomic mass of zinc = 65.39 g/mol The Attempt at a Solution For part (a) I use the fact that...
  32. S

    Atomic Vibration in Einstein & Debye Models

    according to Einstein all atoms in solid vibrating with the same frequency , while in the Debye's mode there are a band of frequency i.e not all the atoms would have the same frequency, my question is that , that is the idea behind the Debye's model? or why the frequency of vibrating of atoms...
  33. S

    Can we see atoms? How do we know they exist?

    Can we see atoms or other atomic stuff like electrons and protons, etc.? If not, how can we know they exist and how they behave?
  34. R

    What's the x-ray diffraction pattern of triangular atoms?

    What would happen to the XRD pattern if instead of having spherical atoms, we had triangular atoms? I found the optical diffraction pattern for a triangular aperture, but I'm not sure if optical diffraction patterns would be the same as XRD patterns.
  35. K

    Absolute zero and vibrating atoms

    I am trying to get a better understanding of what it means for an atom to vibrate. Let's say there is a chunk of iron in deep space that starts out with a temperature of 50 degrees celsius and is rapidly losing thermal energy. I will make the following assumptions: 1. The iron has thermal...
  36. K

    How Do You Calculate the Average Kinetic Energy of Multiple Helium Atoms?

    Homework Statement Write an expression E for the average kinetic energy of Helium atoms using the Boltzmann constant. Homework Equations PV = nRT PV = \frac{1}{3}mN\overline{c^2} k = \frac{R}{N_A} [P - Pressure ; V - Volume ; m - Mass of an atom ; N - Number of atoms ; others have...
  37. N

    Questions about electrically neutral atoms

    Hi, everybody. I wanted to ask you about the question that really tortured me for quite a long time: Does electrically neutral atom have energy above 0? I mean what would happen if you have measuring instruments and they tell you energy is 0, but the energy of atom is still there-potential...
  38. A

    Why nuclear radiations occur in atoms with large nucleus?

    why nuclear radiations occur in atoms with large nucleus?Is it the weakening of residual strong force? If so why it gets weak ?
  39. nealshireman

    What happens to heavy atoms that come into the atmosphere as cosmic

    What happens to atoms such as gold, lead, and other heavy elements when they come into the Earth's atmosphere as cosmic rays traveling at close to the speed of light? I know that supernovas are generally the only natural place where atoms heavier than iron are formed, and they also shoot out...
  40. Nemo's

    Distance between 2 atoms in a crystal

    Homework Statement Given a crystal (cube) with regularly arranged atoms (Total 27 atoms) The mass of each atom is 3.5*10^-25. The density of the crystal is 9.2*10^3 What is the shortest distance between the centres of two adjacent atoms? Homework Equations density = mass / volume The...
  41. DennisN

    Hydrogen Atoms under Magnification (paper)

    (PF members Salman2 and ftr have already mentioned this in two threads, but I think it deserves it's own thread :smile:) Hydrogen Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States Abstract: To describe the microscopic properties of matter, quantum...
  42. P

    Is it possible to build atoms?

    Is it possible to "build" atoms? Was just thinking to myself, the world running out of resources etc... the most basic form of matter is the 3 subatomic particles... and all matter is made up of them. i did some googling but couldn't find much so I am wondering if one day it would be possible...
  43. marcus

    New basis for atoms of spatial geometry (intertwiners)

    Here's the introduction of the paper by Freidel and Hnybida. Quantum geometry is built up of chunks of geometry that contain information relating to volume, areas, angles made with neighbor chunks, etc. The Hilbert space that these chunks (called intertwiners) live in needs a set of basis...
  44. Physicist50

    Extracting Gluons from Atoms

    I was wondering if it was possible to extract individual gluons from a nucleus, and if so, how?
  45. tom.stoer

    Stability of atoms in QM / QED

    It is often stated that quantum mechanics is able to explain the stability of atoms. I think most explanations are cheating b/c the compare apples and oranges. There are two reasons in classical theory which indicate that atoms should be unstable: A) there is no minimum for the orbit; the...
  46. julcab12

    Exotic atoms hold clues to unsolved physics puzzle at the dawn of the

    "... the first direct evidence of pear shaped nuclei in exotic atoms. The findings could advance the search for a new fundamental force in nature that could explain why the Big Bang created more matter than antimatter—-a pivotal imbalance in the history of everything." Any insights...
  47. D

    Photographing Atoms: Closest and Best Photos of Molecules

    What is the most accurate,closest and best photo that exists of an individual atom or molecule? There is the scanning tunneling microscope which is way better than the electron microscope,yet it doesn't photographs them by reflecting light off them,it uses quantum tunneling of electrons.I would...
  48. D

    Using Maxwell Boltzmann distribution to find number of atoms

    Homework Statement You will recall from our discussion of the Franck-Hertz experiment that the energy difference between the first excited state of mercury and the ground state is 4.86 eV. If a sample of mercury vaporized in a flame contains 1.06×1020 atoms in thermal equilibrium at 1563 K...
  49. S

    Why is a single layer of atoms referred to as 2d ?

    Why is a single layer of atoms referred to as "2d"? I commonly hear a single layer of atoms referred to as being a "2-dimensional structure", when it so clearly is not 2-dimensional. Why do people make that obvious mistake? The same exact folks will also tell you that spacetime is a...
  50. Rorshach

    How Far Must Caesium Atoms Be for a 1% Tunneling Probability?

    Here is one problem I have, I think it is simple, but then again I thought that every problem I had was like that only to discover that there was some trick in the middle, so please help. Caesium has exit work Wut = 1.9 eV. This means, therefore, that there are electrons in the cesium such...
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