What is Atoms: Definition and 878 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.

View More On Wikipedia.org
Recent contents Top users
  1. alemsalem

    Can internal energy levels of atoms affect chemical potential of ideal gas?

    μ/T represents the change in entropy if we change the number of particles,, so according to the fundamental assumption of statistical mechanics μ/T should tell us about the tendency of two systems to exchange particles... but I am having a hard time imagining how rotational or vibrational...
  2. C

    What comes out of an 'atomic oven' - atoms, ions?

    Hi, I am trying to make a Magnesium source by curling up a tungsten wire with a block of Mg inside. Then by setting electricity to the tungsten wire, the Mg is heated and you get what out? Magnesium atoms? Magnesium ions? Thanks a lot /Carnot
  3. johann1301

    Faynman talks about atoms repelling and attracting each other

    In this vid, Faynmen explains what a fire really is: just watch from start till 1:22 He says that sometimes carbon repels air(O2) and sometimes they attract each other. If they attract, they start a fire. Whether they do repel or not is dependent by the distance between them or their...
  4. C

    Energy levels hydrogenic atoms

    I don't get why for hydrogenic atoms the 2s and 2p orbitals have the same energy. i do get it mathematically, but I am thinking that the fact that there are angular nodes in 2p and not in 2s MUST affect the energy!
  5. V

    Bohr's model of hydrogen like atoms question.

    Homework Statement A neutron moving with speed v makes head on collision with a hydrogen atom in ground state kept at rest. Find the minimum Kinetic energy of the neutron for which inelastic(completely of partially) collision may take. (mass of neutron=mass of hydrogen=~1.67*10-27)...
  6. D

    Bond angle comparison in sp2 hybridised carbon atoms

    1. Homework Statement This was a question on an exam I took a week ago in inorganic chemistry. The problem statement was like: "We have two molecules, H2CCH2 (ethene) and F2CCF2 (1,1,2,2-tetrafluoroethene). Which bond angle is greater? H-C-H in ethene or F-C-F in 1,1,2,2-tetrafluoroethene?"...
  7. R

    Concentration of Radon in atoms per cubic meter

    Homework Statement i) The average concentration of 222Rn in air inside a building is 20Bqm-3; what is the average concentration of Rn in atoms per cubic meter? ii) In a sealed room of volume 50m3 what activity of 238U in a piece of porous rock would eventually give rise to this 222Rn...
  8. jfy4

    How Does Particle Size Affect Gas Laws in Hard Sphere Models?

    Homework Statement In a classical gas of hard spheres (of diameter D), the spatial distribution of the particles is no longer uncorrelated. Roughly speaking, the presence of n particles in the system leaves only a volume (V − nv_0 ) available for the (n + 1)th particle; clearly, v_0 would be...
  9. T

    [Statistical Physics] Spin-1 atoms in uniform magnetic field

    Homework Statement A crystal contains N atoms which posses spin 1 and magnetic moment \mu. Placed in a uniform magnetic field B the atoms can orient themselves in three directions: parallel, perpendicular, and antiparallel to the field. If the crystal is in thermal equilibrium at temperature...
  10. B

    Why are there clumps of atoms?

    The elements above iron are formed in a supernova. If that is the case, I don't see why we should find lumps of gold, lumps of uranium, lumps of cobalt, lumps of nickel. Why isn't it the case that all elements are just swarming around randomly with normal distribution. I put this under...
  11. N

    Number of atoms in FCC gold cube with only the radius given

    number of atoms in FCC gold cube with only the radius given! 1)it is given that the radius of a gold atom sphere is 144.2 pm, gold is packed in an FCC manner Give the ratio Ns/Nv as a function of L (gold cube side) and a parameter of FCC latice, knowing that Ns is the number of surface...
  12. B

    What if atoms obeyed an inverse-cubed law

    atoms would be impossible in a universe ruled by an inverse-cube law because there would be no stable orbits for electrons. The above sentence comes from Rees' book Just Six Numbers. I don't get it. Why would an inverse-cube law affect the stability of electron orbits?
  13. N

    Number of atoms in FCC gold cube

    Hello i need help in this question it is given that the radius of a gold atom sphere is 144.2 pm, gold is packed in an FCC manner Give the ratio Ns/Nv as a function of L (gold cube side) and a parameter of FCC latice, knowing that Ns is the number of surface atoms and Nv is the...
  14. N

    Atoms made of different Quarks

    Atoms, and therefore matter, is made of protons and neutrons, which are in turn made up of quarks, up and down flavors, is it not possible that other matter may be made up of different quarks, so as to make different atoms, that would be very different to those we already know of and also...
  15. S

    Dynamics of Contracted Atoms, Molecules, etc.

    In Lorentz Ether Theory, object really get contracted, for example, a 6 foot man would become mere 1mm when traveling near the speed of light. They say SR and LET can't be distinguished because the performance of contracted atoms, molecules, etc. would be the same. Meaning if you were mere 1mm...
  16. P

    Magnetic field at a dipole (how many atoms surround the dipole?)

    Homework Statement Consider a paramagnetic material. The magnetic field generated by each dipole in the material is 1/30 T. What is the magnetic field at a given spin, due to the presence of nearby spins? Homework Equations The Attempt at a Solution So I need to multiply 1/30 by...
  17. R

    If all states are stationary, what causes atoms to radiate then?

    We've solved for several systems, the hydrogen atom for instance, and one of the properties of these is that it doesn't matter what excitation state you look at, they are stationary states, the Hamiltonian is constant in time, so where's the impetus on an excited atom to radiate light if it's in...
  18. L

    Interaction between two excited hydrogen atoms

    hi all. i am trying to calculate the interaction between two excited hydrogen atoms, using degenerate perturbation theory. but comes up a few problems, any helps will be greatly appreciated. the perturbation has the form: H`=e3/R3(XaXb+YaYb-2ZaZb) where the R is the distancee between two...
  19. W

    Why perrin's experiment demonstrates the existence of atoms?

    Perrin got his nobel prize because of his experiment on brownian motion, which is thought to have proven the existence of atoms i cannot understand that if you see an array of dots from STM, i believe you demonstrate the existence of atoms but i cannot see why perrin's experiment or...
  20. fluidistic

    Atoms with several electrons, potential energy

    Homework Statement I don't really understand the problem wording. What do they ask me exactly? Here it goes: Consider the potential energy V(r) of an electron in an atom whose atomic number is Z. Calculate the potential energy aproximating the distribution of charge of the others Z-1...
  21. T

    How do Cesium gas atoms demagnetise

    Hello guys :), if we magnetise Cs atoms with a magnetic field (or basically any other method like pumping), and got all the spins (moments) aligned in 1 direction, and then turn the cause of the alignment off, how will the decay profile look like? is it going to be a clean exponential decay...
  22. N

    What is the maximal velocity of atoms with at least one electron?

    Hello, I am looking what maximal velocity was reached for some atoms which have at least 1 electron. It can be ionized atoms, but still must have at least one electron. Thank you.
  23. S

    Calculating the number of atoms in X Kilograms of iron

    Homework Statement I'm having trouble with this. I need to calculate the number of atoms in iron. How do I do this? For example if I had 1 KG of iron, how many atoms are in it? Homework Equations I need to give an answer in scientific notation A x 10^B A being 1 significant...
  24. C

    How to graph potential energy for 2 atoms in diatomic molecule w/ 3 unknowns

    Homework Statement The potential energy of two atoms in a diatomic molecule is approximated by U(r)=a/r^12 - b/r^6, where r is the spacing between the atoms and a and b are positive constants. Find the force F(r) on one atom as a function of r. Make two graphs one of U(r)...
  25. M

    Solid State Physics- Finding concentration of donor atoms (Nd)

    Homework Statement Silicon at T= 300K contains acceptor atoms at a concentration of Na = 5*10^15 cm-3. Donor atoms are added forming an n-type compensated semiconductor such that the fermi level is 0.215 eV below the conduction band edge. What concentration of donor atoms are added...
  26. S

    Amateur question about rearranging atoms

    Hi, I've been thinking about atoms a lot lately, and I've tried to search on internet but did not find any comforting answers yet. So (yes I'm an amateur) there is like 100+ known elements that's possible to combine together to form another compound. My question here is: Would it be...
  27. D

    Finding the Atoms in 1.00 g of CaCO3: Where Did I Go Wrong?

    Homework Statement The total number of atoms in 1.00 g of CaCO3 (MM = 100.0 g/mol) is: The Attempt at a Solution My solution: 1.00 / 100.0 = 0.01, then 0.01 x 6.022x10^23 = 6.022x10^21 atoms. However, the correct answer is 3.01 x 10^22. How was my approach wrong and did I miss any...
  28. B

    2 slow moving hydrogen atoms - distance to start interaction

    At what distance do 2 hydrogen atoms (not ions) begin to attract each other? No, this is not a homework question. I am 58.
  29. X

    Kinetic Energy of Two Atoms System: r=r1

    Homework Statement The figure shows a potential energy curve for the interaction of two neutral atoms. The two-atom system is in a vibrational state indicated by the heavy solid horizontal line. (a) At r = r1, what are the approximate values of the kinetic energy K, the potential energy U...
  30. A

    How do you calculate the temp at which a H2O molecule splits into single atoms?

    Hi I want to figure out how to calculate the temperature at which more energy is required to keep hydrogen and oxygen together (as in the case of H2O) than to separate them...in other words the temperature at which hydrogen and oxygen will no longer combine due to extreme temperatures. How...
  31. I

    Understand Atoms: Get Answers to Your Questions

    I don't understand atoms that well and the thought is so surreal. Can someone please try to help me understand?
  32. 1

    Project: Using 100% of an Atoms energy

    I AM TRYING TO PROGRESS IN THIS PROJECT AND ONLY SEE ONE DIRECTION PLEASE IF YOU HAVE ANY KNOWLEDGE OR THEORY OF THIS PLEASE INCLUDE IT! Edit: personal information deleted I’m a sophomore at High school in Arizona. Although I’m most likely not as smart as most people on this forum, I’m...
  33. T

    How do we know everything in the universe is made of atoms?

    We know everything on Earth is made up of atoms and molecules, and most likely everything in the solar system, but how do we know everything in the universe uses them, and not something else? The Big Bang would cause things to have similarities, but different parts of the universe could still be...
  34. I

    One mole of Lead contains how many atoms

    How many atoms are in one mole of the element Lead(Pb) -Intrepid Elder
  35. liometopum

    Atoms are 'nothing but' space versus 'mostly' space

    It is common to see this line: "atoms are mostly empty space". That line appears inadequate and misleading. Atoms are ultimately made up of electrons and quarks. Electrons and quarks are by definition 'point particles', meaning they have no spatial extent. So there is nothing there that takes...
  36. A

    Are all atoms considered to be isotopes?

    What the title says
  37. jaketodd

    Atoms with non-zero nuclear spin

    What are the criteria for an atom to have non-zero nuclear spin? This is not homework. Thanks, Jake
  38. S

    Atoms Unite: Gas vs. Non-Gas Molecules

    Hello, why much substances have one atom when aren't gas and 2 same atom united when are gas (for example N and N2, O and O2) ? Thanks!
  39. P

    How does light from the sun cause atoms to vibrate?

    Is the reason behind the vibrating the movement of electrons from a stable to a excited state? My quest for knowledge began with this question..."How exactly does light transform into heat--for instance, when sunlight warms up a brick wall? I understand that electrons in the atoms in the wall...
  40. B

    Unravelling the Separation of 35CI19F Atoms: A Problem Solved

    Problem: The adjacent lines in the pure rotational spectrum of 35CI19F are separated by a frequency of 1.12 x 1010 Hz. What is the equilibrium separation of the atoms in this molecule? The attempt at a solution So, the equation I think I need to use to find the equilibrium separation...
  41. A

    Exploring Atoms: Bonding and Forces

    This may be a simple question, but I still haven't a clear answer to it. How do atoms bond together? What force is used to bond them together?? (Please if you could answer both of these questions it would be great.) Thanks.
  42. H

    How are atoms entangled and can it be done remotely?

    I'm a bit confused about quantum entanglement. First of all, how exactly do you entangle two atoms? I've heard about how they entangled atoms in quantum teleportation experiments, but I don't get how they did it. I've heard that the atoms must "interact", but what exactly does that mean? Do they...
  43. R

    Schrodinger equation and atoms

    To what extent does the Schrodinger equation apply to an atom as a whole?
  44. G

    Basic chem. atoms and their electrons.

    This question is pretty straightforward, but I just can't seem to find the answer.. What is the reason that electrons only exist in shells and never between them? A hint that was given to me was to "think about quantum energy". I was thinking because if they wouldn't exist in shells, then...
  45. K

    Normal Zeeman effect of hydrogen atoms

    Homework Statement When specially prepared Hydrogen atoms with their electrons in the 6d state are placed into a strong uniform magnetic field, the degenerate energy levels split into several levels. This is the so called normal Zeeman effect. A) Ignoring the electron spin what is the...
  46. M

    Ionisation of semiconductor atoms

    When we provide thermally or optically en energy higher than the semiconductor bandgap we create elctron-hole pairs, that is electrons are extracted to the valance band and they become free to move inside the crystal. My question is: are the semiconductor atoms then ionized, which means for...
  47. C

    Atoms: Adding to Universe & Changes Explained

    Are there ever atoms being added to the universe? If not could we in the future be able to follow an atom through several different changes that it might experience?
  48. Y

    Atoms and sub-atomic particles.

    I am trying to get the most complete picture of the structure of atom. I understand generally how elements and molecules are formed, however the last thing I was taught about atoms was 10 years ago. I was told about the electron proton and nuetron and that's it. I know this is just the basic...
  49. B

    Atoms in a Solid: Separate but Connected

    how close are the atoms in any solid, is all the space possible in a solid is filled up by its atom finally can we consider an atom an isolated body ,or can size of strings pass between inter atomic spaces.i believe atoms in the solid is not actually in contact but there exists infinitsimally...
  50. S

    Interatomic spacing of iron atoms

    3.2kg of iron is required to make a hollow spherical shell having inner radius (r=3cm).outer radius(r=5cm). i)estimate density of iron. (ans :6.585g/cm^3) -not sure if its correct though ii) using (i),est interatomic spacing of the iron atoms. the atomic mass of iron is 55.9u. need help...
Back
Top