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. S

    Do Atoms Exist in a Perfect Vacuum?

    Do atoms exist in a vacuum?
  2. E

    Volume of a solid based on number of atoms

    This is a silly doubt i guess... Homework Statement When you know an atom's radius you can easily determine its volume by considering it's a sphere. But when you're dealing with solids, that is, a set of atoms... and then you have bands insted of orbitals... this differente...
  3. S

    What is the optimal basis set for a full CI calculation of low Z elements?

    Hi, I running a full CI calculation for low Z elements (up to Ne) in order to obtain the lowest lying electronic energy levels. I can't seem to get correct results even though I'm using 1-electron states from first 4-6 electron shells. I am also using singly and doubly excited...
  4. L

    Does nuclear decay apply to atoms of matter consumed by black holes?

    I can offer no further insight.
  5. D

    How to Solve for Variables Using Derivatives in Atomic Interactions?

    Suppose that the interaction energy between two atoms is given by: E(R)=-A/(R^2)+B/(R^10) The atoms form a stable molecule with an inter- nuclear distance of 0.3nm and a dissociation energy of 4 eV. a) Determine A and B. b) Calculate the force required to break the molecule. What is the...
  6. T

    Fortran Generating Coordinates for Silver Atoms in C and Fortran

    Hello Could anyone help me rewrite following C code to Fortran code? It generates coords for sc silver atoms. #include <stdio.h> #include <math.h> int main(void) { int i, j, k, n = 0; double A = 4.08, L_X = 20.0, L_Y = 20.0, L_Z = 15.0; int iMax = ceil(L_X/A)...
  7. G

    What is the mean speed of hydrogen atoms at 50K?

    Homework Statement Dear all, I have to calculate the mean speed of hydrogen atoms, at temperature of 50K. Homework Equations Of course: <v>=\sqrt{\frac{8k_BT}{\pi m}} The Attempt at a Solution However, when I attempt to calculate it, m=\frac{2}{6.022x10^{23}} k_B=1.3807x10^{-23}...
  8. T

    Calculating energy eigenvalues/eigenstates for multielectron atoms using SCF

    E\Psi(\vec{r_1},\vec{r_2})=(-h^2/2m*\nabla^2+U(\vec{r_1})+U(\vec{r_2})+U_{ee} (\vec{r_1},\vec{r_2}))\Psi(\vec{r_1},\vec{r_2}) Now this is the equation for a 2 electron system, and [tex]U(\vec{r_1})[\tex] and [tex]U(\vec{r_2})[\tex] are the nuclear potentials for the 2 electrons and U_ee are...
  9. C

    Correct me if I am wrong, but atoms emit photons when they jump energy

    Correct me if I am wrong, but atoms emit photons when they jump energy levels. Right?
  10. C

    Cold Atoms Research: Overview & Developments

    Hello PF readers, Could anyone enlighten me on this specific field of research in physics? I am particularly interested how new/old this field is, current developments, major theories/models/predictions motivating the research, obstacles if any, the saturation of the field? Thanks in...
  11. B

    Most probable speed of aluminium atoms

    Homework Statement Aluminium atoms at 1173K enter a vacuum chamber. Calculate the most probable speed for the atoms. Homework Equations vmp=\sqrt{}(2kT/m) The Attempt at a Solution The molar mass of aluminium is 0.0270kg mol^-1, so vmp=\sqrt{}(2*1.381*10^-23JK^-1)*1173K/0.0270kg...
  12. S

    Nuclear decay and the age of atoms.

    Nuclear decay and the "age" of atoms. All atomic nuclei heavier than hydrogen were created in stars and would therefore seem to have different ages relative to some specific spacetime reference. Nuclear decay wrt a single atom is taken to be a temporally random event, but is it plausible to...
  13. H

    How does something become tangible? How many atoms are needed to be

    How does something become tangible? How many atoms are needed to be able to see/hold something?
  14. M

    Splitting Atoms: Exploring the Strong Force

    If the strong force is what is used to describe the attraction in the atomic nucleus, how is it possible to split atoms without them constantly re-pairing? a free charge doesn't seem like it would exist due to the strong force. I'm missing something right?
  15. O

    Calculating Mass: Comparing 20 g of H2SO3 to 20 mol of HCl

    1) where i got more atoms in 20 gr H2SO3 or in 20 mol of HCl ? 2) tell me if i Right: the mass (in gr) of 100 Molecules Of SO2(g) is: the mass of O2=31.998, the mass of S=32.065. so Together the mass is about 31.998+32.065*100=6406.3 but i don't sure how to Change it to (gr) unit...
  16. Z

    Exploring Anti-Matter: Why Aren't Atoms Composed of Positrons & Antiprotons?

    I've recently learned more about antimatter, namely what types there are, and one question has stuck in my mind: why are atoms not composed of Positrons and Antiprotons? Since scientists at the LHC recently were able to contain antihydrogen, it seems that these atoms, while isolated from matter...
  17. A

    Atoms of anti-matter trapped for first time.

    Anti-hydrogen atoms have been trapped/stored for the first time at CERN. http://newscenter.lbl.gov/news-releases/2010/11/17/antimatter-atoms/
  18. J

    How can light cause atoms to oscillate without being absorbed?

    If light travels through a perfectly transparent material, it will not be absorbed, and other than the reflection loss at the two interfaces, the energy that comes out will be equal to that which went in. Yet we know that the light field is causing all the atoms in its path to oscillate, thus...
  19. K

    Creating Patterns with Atoms: Can We Do It?

    Can we move atoms into any pattern we want? Thanks!
  20. T

    SHM in atoms question I think my textbook is wrong :0 yet again.

    Homework Statement In a simple atomic model of a solid, the atoms vibrate with a frequency of 2E-11 Hz. The amplitude of the vibration of the atoms is 5.5E-10 m and the mass of each atom is 4.8E-26. Calculate the total energy of the oscillations of an atom. Homework Equations total...
  21. L

    How Old Are The Atoms In Our Body?

    How "Old" Are The Atoms In Our Body? Richard Feynman once said, "So what is this mind of ours: what are these atoms with consciousness? Last week’s potatoes! They now can remember what was going on in my mind a year ago — a mind which has long ago been replaced. To note that the thing I call...
  22. K

    What's the motivation of using silver atoms in the Stern-Gerlach experiment？

    Historically the experiment was performed on silver atoms, but what's the reason of using silver?
  23. E

    Photons and and equivalent number of atoms on gravity

    due to e=mc2 would massless photons and an equivalent number of mass-energy atoms have the same effects on gravity? Does mass play any special role in gravity or only energy?
  24. M

    Why do Atoms Stay in Lowest Potential Energy State?

    I have a question that I couldn't find in my textbook. Say for example a hydrogen atom. If it is excited the electron will jump to a higher quantum level and as it relaxes it will release a photon proportional to the potential energy gained in the higher quantum level... My question is why...
  25. K

    Is it possible: ionizing atoms in free-air

    Alright here's a question for everyone that has some input. Can we ionize atoms, say hydrogen, in free air? This is hard to explain, but can we make plasma in the regular atmosphere? Thats the only way I can word it. So is it possible?
  26. L

    Atoms & Sound Waves: Science vs Religion

    In an argument of sorts with another college classmate, please help. We were argueing science and religion. She stated that all life is made up of atoms, and atoms are now shown to be made up of soundwaves also. Not possible correct?
  27. B

    Atoms in Biology - Questions Answered

    I was just curious about atoms in biology. Do organisms have the same atoms all the time? Or are they always changing? When we eat do we gain new atoms etc. Sorry if this is a dumb question. I can't find anything on it maybe because it is to easy.
  28. Jadaav

    Why do we use/calculate the atoms of an element to balance an equation

    Hi guys, I wanted to know these things with their respective examples : 1. What is an atom ? 2. What is a particle ? 3. Why do we use/calculate the atoms of an element to balance an equation ? Please answer to these questions guys, because I only have 2 days for my exams and to know them.
  29. S

    Chemistry How many moles of C atoms are there in 0.47 mole of Arginine

    Arginine has a molecular formula od C6H14N4O2 How many moles of C atoms are there in 0.47 mole of arginine What is the equation I would use here
  30. T

    Why Atoms Come Together: Understanding Matter Formation in Nature

    Hi all. I was hoping you mat be able to help me with a question. If matter is made up of atoms, why do these atoms come together to form different matter? For example, why do some atoms form a brain whilst others form skin? How do these atoms know, if you like, what to form? Why do some...
  31. H

    Calculate electric force between unlike atoms of a molecule?

    How can I calculate the attractive electric force between the unlike atoms of a water molecule? Would I use Coulomb's law? Using Coulomb's law: I don't understand the radius I would use?
  32. D

    Question about excited atoms etc.

    A quick question... When you excite electrons or so in molecules, atoms etc., do the molecule/atom change, or what does happen ? I mean, if you have water, and excite an electron, do it turn from "liquid" to "gas", or the other way around, or doesn't it change its structure or what you can...
  33. B

    Atoms and Programming: Exploring the Unknown

    In my computer science class my prof rambled off into examples, one of which was atoms. He said that atoms were just a model for something that we really can't understand yet. Is this correct or is he under some kind of influence or a complete idiot (likely, he teaches programming 'backwards').
  34. FeDeX_LaTeX

    Can Atoms Be Moved and Imaged Despite Wave-Particle Duality?

    "Moving Individual Atoms"? Hello; I recently read an article about this video - IBM moving individual xenon atoms to create the IBM logo. I'm not sure I understand what they're doing in this video - are they using a computer to simulate/show what this would look like if the atoms really...
  35. L

    Atoms that make up the body do they come from

    hello I am very new to this stuff and i hear that atoms make up everything we know . but i was wondering about the atoms that make up our bodys do they come from what we eat and maybe the sun and we make them into what we need to grow and live ? or can completely new atoms be created within the...
  36. N

    Temperature is base on the average kinetic motion of all atoms

    Sorry for this silly question , I am still high school student . I know that temperature is base on the average kinetic motion of all atoms. But kinetic motion is not absolute so in what case should we use this formula: v= \sqrt{\frac{3RT}{\mu}} . Should it be the velocity in respect to the...
  37. H

    Coulomb force vs. Pauli principle in atoms

    Homework Statement In the absence of the Pauli principle, the Coulomb force would not be saturated, and the energy of a system containing N atoms would vary as N^(5/3). Show that a system of 2N atoms would have an energy lower than that of two N - atom systems. Homework Equations E...
  38. M

    Can atoms reach absolute zero energy and what happens then?

    If you placed an atom in an empty universe that was completely dark and cold, would it eventually radiate away all its energy until it had zero KE? If so, what would happen to an atom with zero energy? In this sense, are atoms inherently unstable systems?
  39. C

    How many hydrogen atoms are there in a 5 sample of pure hydrogen?

    How many hydrogen atoms are there in a 5 sample of pure hydrogen?
  40. K

    Estimation of number of Carbon atoms in bacterium

    Homework Statement Minimal growth medium for bacteria such as E. coli includes various salts with characteristic concentrations of mM and carbon source. This carbon source is typically glucose and it is used at 0.2% ( a concentration of 0.2g/100mL). a) Make an estimate of the number of...
  41. I

    Where did the energy and mass in the singularity come from?

    What caused it to suddenly create a universe? What caused the singularity to change into the Big Bang? Can anyone explain how all the mass-energy was accumulated into the "singularity"? Where did the Energy in singularity come from? Could it be that human cosmologists are only stating an...
  42. B

    Heat: Vibration of Atoms or Electromagnetic Radiation?

    So heat is vibration of atoms in lattice (or fluid). Heat is also electromagnetic radiation. Do we say "heat is electromagnetic radiation", or is that incorrect, since heat is vibration of atoms in lattice? Should we say "heat is __spread by__ electromagnetic radiation instead?
  43. N

    Will electrons fly out of atoms and planets lose orbit?

    Hello, I'll take you've heard of the heat death of the universe. Now I was wondering: will electrons actually, at some point, leave their atom? If so, is this solely due to the fact that the quantum mechanical chance of an electron being out of an atom is not zero and thus, according to...
  44. M

    Order of atoms in chemical formulas

    what determines what order the atoms in a formula are written? for example, why is it CO2 and not O2C? It doesn't appear to be ordered by atomic weight, place on the peridoic table or alphabetically so what is it?
  45. W

    Atoms tunnelling through a metal surface

    Hey guys.i have heard it has been experimentally proved that even atoms can tunnel through a metal surface.I tried searching all over the web but just could not get any references on that.So,is that true?if somebody know where i can read more about that experimental proof,please point it out...
  46. B

    If the atoms in solid matter a tightly grouped?

    Why don't the electrons ever hit each other,and when they do what happens? Do the atoms sometimes have more electrons than protons because other electrons from other atoms come close to it and get caught in its orbitals?
  47. J

    Can we remove/add electrons and protons from/to atoms to create other materials?

    Example: Take a hydrogen atom and make it a carbon atom. Can we do it with our current technology? If so, how do they do it?
  48. T

    Can We See Atoms? Exploring the Possibility

    Cant we see atoms?? In a book I read that theoretically it is not possible to see atoms even if high quality microscopes are used. So why is that?
  49. J

    How possible when atoms come together in certain way to produce conscious being

    I'm not a science student. Therefore, please keep your reply simple and straightforward so that your help and guidance can be appreciated to the fullest. Thank you. I don't know if it's the right forum to ask this question. My question is not exactly about the origin of life rather it's...
  50. A

    Ratio of the number of atoms in the n = 2 energy level

    Homework Statement a) Consider a sample of hydrogen atoms at a temperature of 300 K. i) What is the ratio of the number of atoms in the n = 2 energy level to those in the n = 1 level? ii) At what temperature would the ratio be 1/10? b) Assume that the conduction electrons in...
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