Atoms Definition and 880 Threads

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

    Are Atoms Truly Devoid of Random Details?

    Atoms have no random details ? If you look at anything macroscopic there is a lot of random details. Like the leaves on a road, or the cracks in a wall etc. Why don't atoms have any random details? They are perfectly round with "points" (electrons) that circulate them. OK, they are not...
  2. D

    Internal motion of atoms and collisions

    I was thinking , if we take into account oly the internal motion of atoms , all collisions will turn out to be elastic. Wont they be?
  3. M

    Big Bang Theory: Exploring the Creation of Atoms

    All right, so what I don't understand about the big bang theory is that when it describes the creation of atoms, does it mean that the particles were already in existence and the explosin only made the particles come together? or were the particles actually created by the big bang? If the...
  4. bayan

    Can't Make Steel By Transmuting Atoms: Betting $20 On It!

    Me mate says that that you can make Steal from mixing Carbon atom and Oxygen (Transmution) :eek: Basicly stuffing arround with nuclues. As far as I can remember you can't touch the nuclues as the EM forces are too strong. How wrong is he? We made a bet of $20 :smile:
  5. K

    Do molecules, subatomic particle and atoms travel in constant velocity?

    The question is the title.
  6. M

    Calculating Deuterium Atoms in 4 kg Ocean Water and Energy Needs of US

    this is homework problem I'm having some trouble with... i haven't had chemistry yet so I'm not sure how i could convert atoms into kg, and the textbook i have doesn't do any examples of problems like this one... i don't even know where to begin. Deuterium (A=2, Z=1) is an attractive fuel for...
  7. P

    He atoms move faster than all of the Ne atoms

    In a mixture of Ne and He at equilibrium, all of the He atoms move faster than all of the Ne atoms. Why is this false? Shouldn't it be true, since Ne atom is heavier than He atom. Thanks for any help
  8. P

    Gravity Effects on Atoms: Extent & Impact

    I wish to know whether gravity has any effect on atoms? And if so to what extent ?
  9. Q

    Stablizing Exotic atoms Impossible?

    I was thinking if you entangled both the electron and positron in a states that both of their orbitals don't interact. Or just entangle the electron with a helium higher orbital electron. Or you entangled a muon with a helium proton(is that even possible?). Is there any way to keep a...
  10. P

    Decrease in entropy atoms problem

    If one could observe the individual atoms making up a piece of matter and note that during a process of change their motion somehow became more orderly, than one may assume which of the following in regard to the system? a. increase in entropy b. decrease in entropy c. gains in thermal energy...
  11. S

    Exploring Atoms: Fact or Fiction?

    I'm doing an assignment for grade 8 science in which I have to prove whether or not atoms are fact or fiction. I was just wondering if anyone would be able to give me a few tips to help me out with this. :smile:
  12. R

    Can Fission and Fusion Transform Radioactive Atoms into Stable Ones?

    Hi, i understand that fission breaks apart radioactive atoms into smaller 'slightly more stable' atoms.. and that this process continues until the atoms break down into stable atoms.. i have been wondering if a radioactive atom/isotope once broken down into a stable atom/isotope would...
  13. G

    Heat Radiation by Groups of Atoms

    Does anybody have any thoughts on why atoms that are warm need to radiate heat in order to stop vibrating or bond back together? The obvious example is the thermos. That is a thermos has the hot liquid contained in a glass container with a mirrored surface towards the inside and then a...
  14. M

    Atoms & Ions Radius: Arranging in Order of Increasing Radius

    I am to arrange the following atoms or ions in order of increasing radius...then give an explanation for the position of S2- in relation to the atoms or ions that come before or after it. Here is what i have so far...in order of increasing radius. K+ K O S2- Cl Now I am not sure...
  15. C

    Needing images of atoms for project

    I am looking for ways to illustrate the chemical makeup of minerals. I belong to a mineral club and I am scheduled to give a presentation to the children about the polymorph mineral group of Kyanite, Andalusite, and Sillimanite. I would like to have images of the atoms that make up these...
  16. R

    Photon Absorption & Excitation of Electrons in Atoms

    When a photon hits an atom it gets absorbed and an electron moves one or more shells up depending on the energy of the photon. When a bigger, many-electron atom gets hit by a photon, can the electrons in the lower shells get excited? I mean when they move up they have to remove the electrons in...
  17. R

    Exploring Consciousness: From Atoms to Inanimate Objects

    Since my brain is made of atoms I question as to whether atoms are conscious, at least in the brain but possibly even in inanimate objects, possibly varying levels of self awareness.
  18. Adrian Baker

    Expanding universe expanding atoms

    I'm trying hard to find a decent explanation for someone that an expanding universe doesn't mean that galaxies get stretched out and made bigger; that the planets won't get further away from the sun; that we don't grow bigger etc. I've googled and searched about but a decent explanation of...
  19. B

    New to atoms - Looking for some advice/clarity

    Hey, I've just been studying the Bohr model at school and have had a nagging thought in my head. If we have electrons wizzing around an atom. They will slowly collapse into the nucleus (due to gravity & magnetic forces of attraction) and well I guess something will happen that won't...
  20. L

    Why aren't atoms magnets? dont their electrons generate magnetic fields?

    help pls! since electrons cr8 a magnetic field due to their spin, shouldn't atoms be magnetic? o0
  21. S

    Atoms whose protons have been stripped off can fuse?

    A plasma consists of both ions and uncharged particles of gases. Is it possible for the uncharged particles to fuse or only atoms whose protons have been stripped off can fuse?
  22. S

    Unveiling the Nuclear Force Acting on Atoms' Nuclei

    How do we determine the magnitude of the nuclear force acting on the nucleus of an atom?
  23. wolram

    Testing gravity theories with Anti atoms

    http://xxx.sf.nchc.gov.tw/pdf/hep-ex/0503034 This paper is a review of anti hydrogen production, and how it could be used to test gravity theories.
  24. W

    Do hydrogen atoms continuously emit radiation?

    Three (3) Questions: 1. Keeping in mind the light emitted by Synchrotrons, then taking the electron as a point charge, and assuming that it orbits the proton in accord with a proper 1s type wave function, does that electron continuously emit (and/or absorb) radiation other than virtual pairs...
  25. G

    What Happens if Electrons and Protons Had Different Charges?

    Because the charges on the electron and proton have the same absolute value, atoms are electrically neutral. Suppose this were not exactly true, and the absolute charge of the electron were less than the charge of the proton by (1.50e-5)e. now its a 4 part question, i think i can do the...
  26. U

    Can Atoms Exist Inside a Black Hole Singularity?

    I've got a question ... if atoms cannot be compacted, beyond a certain minute level, how can they exist inside a black hole, and particularly at the 'singularity' point? Wouldn't the fact that atoms cannot be compacted below a certain level falsify the hypothesis of a singularity at the centre...
  27. wasteofo2

    What's in the space between atoms, or between nuclei and electrons?

    Is it known what's between atoms, or between the nuclei of atoms and their electrons? There's a great deal of space (relative to the size of the particles) between the electrons of an atom and it's nuclei, so are there some particles in those spaces, or is it essentially a vacuum? Thanks...
  28. Q

    Atoms: Destruction & Transformation

    Where do atoms go after they have been destroyed for use of the atom bomb, or anything else that destroys atoms. Does the things that make up an atom disaper or form another atom. thanks, quantumgenius
  29. U

    Atoms, Black Holes and Singularities: A Historian's Questions

    I have a question ... if atoms cannot be compacted, beyond a certain minute level, how could they exist inside a black hole, and particularly at the 'singularity' point? Does the fact, that atoms cannot be compressed beyond a certain point, suggest falsification of the hypothetical singularity...
  30. P

    Br2, is known to contain two atoms of bromine

    I have no idea how to do this...any ideas?
  31. K

    Atoms vs Elements: Explaining the Difference

    Guess I'll be flippin' burgers for the rest of my life guys... I can't figure out the difference between elements and atoms! I've searched the internet and wrote down their definitions and I e-mailed my prof. Here is how he explained it: > Atoms are the fundamental building blocks of matter...
  32. J

    Exploring Hybrid Atoms: Matter and Antimatter Composition in Nuclei

    [SOLVED] Hybrid Atoms I should like to know your opinion about the possibility of the existence of atoms whose nuclii are composed of matter and antimatter components (simultaneously). Which and where experiences had been made about it. Thank you.
  33. V

    Calculating Mass of Carbon 12 Atoms

    What is the mass (in grams) of 6.022 x 10^6 atoms Carbon 12? I am given the equation 1 amu=1.6606 x 10^-24 g, but I'm not sure if I should be using this in my conversion factor or not. Can anyone tell me how to set this up? I have a few ideas but unfortunately I don't have any way to check my...
  34. Y

    Quantum mech help - radii of some atoms

    What is the ratio of the radii of muonic hydrogen to hydrogen? Muonic hydrogen consists of a proton and \mu^{-}. How do you calculate this??
  35. R

    Electrons in Atoms: Do They Have a Current?

    Do the electrons revolving around the nucleus have a current associated with them?
  36. M

    String Theory: A Revolutionary View of Atoms

    String Theory! ok am I getting this right? when people talk about string theory they say that atoms instead of being made out of orbs particles they are waves coming from a fundamental string.
  37. J

    Time and Atoms: Can they exist without each other

    This is a question regarding time and atoms. My question is this: if one were able to stop the occurence of time, or maybe even reverse time, since the atom in forward time is constantly in motion, would the altering of this forward motion cause the atom to fall apart. Would the covalent bonds...
  38. R

    Lewis Structure Problem, Atoms of more than 8 valence electrons?

    I am confused. Doing Lewis structures is like balancing an equation, putting it together till all the valence electrons work with each other, as far as I can tell. :-p However, some atoms have A TON of valence electrons, like gold which has 25, um, how would I connect it to other elements...
  39. D

    Unraveling the Mysteries of Electrons in Atoms

    In trying to understand the oscillating electron in any atomic structure you need to remember that the electron is not just orbiting and controlled by the nucleus but has a spiraling velocity along with the nucleus as the atom accellerates in its path through the heavens (Universe). This...
  40. M

    BECs vs He-4 Atoms: What's the Difference?

    From what I know, the cooling of He-4 atoms causes them to fall into the ground state, making them Bosons. But there's something which confuses me, from what I read, these atoms actually coalesce into one "super-atom". And in quantum theory, it is entirely possible for many atoms to be in one...
  41. C

    Why Don't Electrons in Atoms Orbit Like Planets?

    Right, as we know from the uncertainty principle we don't know exactly where an electron is, just where it most probably is. This implies that electrons don't follow circular paths like those of planets round the sun (as in the rutherford model) - they must take a more random path. My...
  42. M

    Chemical reaction of 2 H atoms.

    2 H atoms can form a H2 molecule, releasing energy of 5 eV. However, no chemical reaction occurs when 2 isolated H atmos collide! Explain this curious result using the conservation laws. first of all, i don't know what conservation law to use for this question. 2nd i think i don't have much...
  43. E

    Calculating Electron Speed in Hydrogen-like Atoms

    Here's my problem: Show that the speed of an electron in the nth Bohr orbit of hydrogen is (alpha*c)/n, where alpha is the fine structure constant. What would be the speed in a hydrogenlike atom with a nuclear charge of Ze? We didn't talk about the fine structure constant in class, so could...
  44. wasteofo2

    Atomic Mass of Neon: Explained for High School Chemistry

    I'm a high school kid taking chemistry, and I'm confused about how atoms get their listed mass. Take Neon for instance, it's got 10 protons, 10 neutrons, and 10 electroncs, it's normally not an ion or isotopic. So from what my teacher's explained, Neon shold have an Atomic Mass of 10 from the...
  45. H

    Actual Distance Between Atoms of an Ideal Gas

    Hi, I am working on a project in which I need to know the distance between the particles in an ideal gas system. I have tried searching (google) for it but was unable to come with any actual values, just general terms. Can anyone refer me to where I might find this? Thanks
  46. G

    Calculating the Number of Atoms in a 12 kg Cat

    I have to approximately figure out, to the nearest order of magnitude, how many moles of atoms there are in a 12 kg cat.You are also told that The masses of a hydrogen atom, an oxygen atom, and a carbon atom are 1.0 u, 16 u, and 12 u. . all i know is that 1 u=1.66 x 10^-27 kg. From here I...
  47. C

    Atoms and Heat: How Temperature Affects Motion

    Why do atoms move faster in a higher temperature? If an atom was initially not moving at all, and then heat was applied to it, would it start moving? If so, what direction will it move in?
  48. D

    Electron Energy in Atoms: What is it?

    What energy do electrons poses in atoms?
  49. N

    Are Photons Responsible for Preventing Atomic Collapse?

    I read recently that photons are largely responsible for why matter doesn't collapse in on itself!? For example, the electrons (negatively charged) and protons (positively charged) inside each of the atoms that make up our bodies should ordinarily attract each other and thereby cause us to...
  50. T

    Rms speeds at 20 degrees celcius of atoms of helium

    1. Calculate the rms speeds at 20 degrees celcius of atoms of helium (4u)? 2. The escapte speed from the surface of the Earth is 11.2 km/s. Find at what temp. the following gas (O2) have this value as the rms speed? 3. One mole of an ideal monatomic gas is heated from 0 degrees celcius...
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